Issued 14 September 2023

August 2023 Palmer Z-Index
U.S. Percent Area Wet or Dry January 1996 - August 2023
August 2023 /monitoring-content/sotc/drought/2023/08/la-p-reg016dv00elem01-08082023.gif

Please note that the values presented in this report are based on preliminary data. They will change when the final data are processed, but will not be replaced on these pages.

National Drought Highlights

Detailed Drought Overview

The upper-level atmospheric circulation over North America during August 2023 consisted of a strong ridge of high pressure, which was anchored over the southern CONUS, and migrating shortwave troughs and closed lows that moved through the jet-stream flow across southern Canada. The ridge axis wobbled back and forth depending on the strength and path of the troughs and closed lows, sometimes extending across western North America and at other times across the eastern CONUS, but for most of the month the ridge remained anchored over the southern Plains to Lower Mississippi Valley. When averaged over the entire month, the ridge extended from the southern Plains and northern Mexico, northward across the Rocky Mountains and into western Canada and eastern Alaska. Unusually hot to record hot temperatures accompanied the ridge. The relentless heat persisted across the southern Plains to Lower Mississippi Valley, sometimes extending across the West and at other times over the Plains to East Coast. The ridge also inhibited precipitation. Cooler temperatures and above-normal precipitation came with the upper-level troughs and closed lows, as well as several tropical systems, interrupting the reign of the ridge in several places. Cold fronts and surface lows, that accompanied the upper-level troughs and lows, brought cooler-than-normal temperatures and above-normal precipitation to areas from the Mid-Mississippi Valley to Northeast. Upper-level troughs and moisture from what was Hurricane Hilary spread below-normal temperatures and above-normal precipitation across parts to much of the West. Tropical Storm Harold brought rain to southern Texas at mid-month, while Hurricane Idalia soaked coastal parts of the Southeast at the end of the month. For the month as a whole, temperatures averaged above normal across the Pacific Northwest, Upper Mississippi Valley, and from the Southwest to Southeast. August 2023 was drier than normal across coastal parts of the Northwest, much of the Upper Mississippi Valley, parts of the Mid-Atlantic states, and most of the Southwest, southern Plains, and Gulf of Mexico states. The North American ridge was part of a subtropical ridge system that extended eastward across the Caribbean and westward into the North Pacific, which brought warmer- and drier-than-normal weather to the U.S. Virgin Islands and parts of Puerto Rico, and a drier-than-normal month to Hawaii.

The drier- and warmer-than-normal weather contributed to numerous wildfires across the West and South (wildfire maps for August 1, 9, 14-a, 14-b, 28-a, 28-b, 31-a, 31-b), in eastern Alaska (wildfire maps for August 9, 14, 28, 31), and Hawaii (wildfire maps for August 9 and 28). In spite of the fire activity, the number of fires and total acreage burned for the year-to-date is still below the ten-year average. The heat increased evapotranspiration (EDDI, ESI), especially in the South, Pacific coast, Midwest, and Mid-Atlantic, further drying soils (USDA topsoil percentages, USDA subsoil percentages, CropCASMA topsoil, CropCASMA subsoil, GRACE root zone, GRACE surface soil moisture, CPC model, NLDAS model, VIC model, QuickDRI, SPoRT layer 1, SPoRT layer 2, SPoRT layer 3, SPoRT layer 4, SMOS observations) and desiccating vegetation (VHI, stressed vegetation). Streamflow and groundwater (USGS well observations, GRACE satellite estimations) were also low in these areas. These conditions were not limited to the U.S. The ridge affected much of North America, with wildfires, desiccated vegetation, and low groundwater and soil moisture extending across much of Canada and Mexico.

The above-normal precipitation in August resulted in contraction or reduction of the intensity of drought over parts of California, Puerto Rico, and the Great Basin, central Plains, Mid-Mississippi Valley, eastern Great Lakes, and Northeast. Drought or abnormal dryness intensified or expanded in Hawaii, the Pacific Northwest, northern tier states, Upper Mississippi Valley, and Mid-Atlantic, and especially from the Southwest and southern Plains to Gulf of Mexico Coast. Drought expansion exceeded contraction with the USDM-based national moderate-to-exceptional drought footprint across the CONUS increasing from 28.1% at the end of July to 34.3% at the end of August (from 23.5% to 28.8% for the 50 states and Puerto Rico).

According to the Palmer Drought Index, which goes back to the beginning of the 20th century, about 29.4% of the CONUS was in moderate to extreme drought at the end of August, which is an increase compared to the end of July.

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Drought conditions at the end of August, as depicted on the August 29, 2023 USDM map, included the following core drought and abnormally dry areas:

August 2023 /monitoring-content/sotc/drought/2023/08/20230829_usdm.png

Palmer Drought Index

The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months.

While both the PDSI and PHDI indices show long-term moisture conditions, the PDSI depicts meteorological drought while the PHDI depicts hydrological drought. The PDSI map may show less severe and extensive drought (as well as wet spell conditions) in some parts of the country than the PHDI map because the meteorological conditions that produce drought and wet spell conditions are not as long-lasting as the hydrological impacts.

August 2023 Palmer Z-Index
August 2023 PHDI

Used together, the Palmer Z Index and PHDI maps show that short-term drought occurred in the Pacific Northwest coast, Upper Mississippi Valley to western Great Lakes, and Southwest to northern Florida, expanding or intensifying long-term drought (PHDI maps for August compared to July). Short-term wet conditions occurred from southern California to the northern Plains, and from the eastern Great Lakes to New England, maintaining or expanding long-term wet conditions, and from the Mid-Mississippi Valley to coastal South Carolina, contracting or reducing the intensity of long-term drought in some of those areas.

August 2023 Palmer Z-Index
August 2023 PHDI

Standardized Precipitation Index

The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months.

August 2023 SPI
July-August 2023 SPI
June-August 2023 SPI
March-August 2023 SPI

The SPI maps illustrate how moisture conditions have varied considerably through time and space over the last two years. Dryness is evident across parts to most of the Southwest and southern Plains to central Gulf of Mexico Coast at all time scales, especially 1-6 and 24 months. Parts to most of the Upper Mississippi Valley are dry at all time scales, especially 1-6 and 12 months. Parts of the central Plains are dry at 6 to 24 months, especially at the longer time scales. Dryness can be seen across coastal parts of the Pacific Northwest at 2 to 12 months, parts of the northern Plains at 2 to 12 months, and in parts of the Mid-Atlantic at most time scales. Much of the West and much of the Northeast are wet at all time scales; western parts of the Great Plains are wet at 1- to 12-month time scales with parts of the northern parts of the Plains wet at 24 months; and wet conditions extend from the Mid-Mississippi Valley to southern Appalachians at 1- to 2-month time scales and from much of the Tennessee Valley to South Carolina coast at 3 to 24 months.

December 2022-August 2023 SPI
September 2022-August 2023 SPI
September 2021-August 2023 SPI

Standardized Precipitation Evapotranspiration Index

The SPI measures water supply (precipitation), while the SPEI (Standardized Precipitation Evapotranspiration Index) measures the combination of water supply (precipitation) and water demand (evapotranspiration as computed from temperature). Warmer temperatures tend to increase evapotranspiration, which generally makes droughts more intense.

For the Northern Hemisphere, August marks the end of climatological summer, which is the season when evapotranspiration reaches its annual maximum. During August 2023, temperatures were warmer than normal for much of the Southwest, southern Plains, Gulf of Mexico Coast, Pacific Coast, and northern Rockies, with record warm temperatures occurring from Texas to Florida and along the Pacific Northwest Coast. Much of the region from New Mexico to Florida, as well as the coastal Northwest, was drier than normal, with record dryness occurring locally along the Gulf of Mexico coast. The combination of increased evapotranspiration due to the heat, and lack of precipitation, resulted in more severe SPEI values than SPI values in the South and along the Pacific Northwest coast during August. The combination of low precipitation and above-normal temperatures over the last 3 to 4 months continued the pattern of more extreme SPEI than SPI in these regions. Temperatures moderated in the West at the 6- to 12-month time scales, and precipitation deficits were not as severe in the south at these time scales, so the SPEI and SPI patterns were of similar magnitude across most of the CONUS (SPEI maps for the last 1, 3, 4, 6, 9, 12 months) (SPI maps for the last 1, 3, 4, 6, 9, 12 months).

The SPEI at the 1- to 4-month time scales was more extreme than the SPI for Louisiana, Texas, and New Mexico, and parts of Arizona, Oregon, and Washington. In some cases, the SPEI was record dry whereas the SPI was not:

The last 2 to 3 years have been extremely dry in the central Plains — so dry, in fact, that the SPI is more extreme than the corresponding SPEI in spite of temperatures being above normal (24-month statewide temperature ranks, divisional temperature ranks, statewide precipitation ranks, divisional precipitation ranks, SPEI, SPI) (36-month statewide temperature ranks, divisional temperature ranks, statewide precipitation ranks, divisional precipitation ranks, SPEI, SPI). In the southern Plains (Texas), the temperature anomalies were hot enough to make the SPEI more extreme than the SPI at these time scales. Locally, parts of Texas had a record dry SPEI.

For the western U.S., the last 12 months have seen temperatures that were near the long-term average, but most of the last 10 to 20 years have been a period of unusually warm temperatures across the West. There have also been periods of extreme dryness westwide during this period (this year being an exception). The combination of excessive heat and dryness has resulted in more extreme SPEI values than SPI values for the last 2 to 6 years (SPEI maps for last 24, 36, 48, 60, 72 months) (SPI maps for last 24, 36, 48, 60, 72 months). This is especially the case for parts of California, the Pacific Northwest, and Southwest. For example, Oregon climate division 3 (Southwestern Valleys) had the third most extreme 72-month SPEI but a corresponding SPI that was not as extreme and ranked sixth driest.

Regional Discussion

Western United States

August 2023 was wet across much of the West, but for the most part the precipitation fell over areas that were not in drought. The Pacific Northwest and Southwest have been dry for the last several months, and parts of these regions were dry in August, so drought expanded in these areas, increasing the drought area across the West as a whole from 15.0% at the end of July to 22.1% at the end of August (based on the Palmer Drought Index). The drought area of the West changed from 21.1% to 30.8%, based on the USDM.

Upper Mississippi River Basin

August 2023 was drier and warmer than normal across much of the Upper Mississippi River Valley. The dryness and heat have persisted for the last several months, with the basin having the eleventh driest and 43rd warmest June-August, tenth driest and 44th warmest March-August, and 22nd driest and 19th warmest September-August in the 1895-2023 record. According to the Palmer Drought Index, 50.0% of the basin was in moderate to extreme drought at the end of August; this is more than the end of July. Based on the USDM, 64.6% of the basin was in moderate to exceptional drought, which is less than last month.

Rio Grande River Basin

At the other end of the country, the Rio Grande River Basin had the third driest and second warmest June-August, and eighth driest and eighth warmest January-August in the 129-year record. The Rio Grande Basin has been in cyclical drought for many years. The last several months have seen a rapid increase in drought area, with the Palmer Drought Index indicating 96.1% of the basin was in moderate to extreme drought at the end of August and the USDM saying 86.0% of the basin was in moderate to exceptional drought. Both of these values are greater than they were last month.

Great Plains

The Great Plains region has been unusually dry for much of the last 3 to 4 years. Beneficial precipitation has fallen in recent months, especially in western and northern areas. But southern areas have been extremely dry. This has given the region as a whole precipitation ranks in the mid-range of the historical record — August ranked 55th driest but 14th warmest, March-August ranked 66th driest and 46th warmest, and September-August ranked 50th driest and 37th warmest. The drought area had been decreasing, but this month the Palmer Drought Index showed an increase to 36.6% of the region in moderate to extreme drought at the end of August.

Hawaii

Drier-than-normal conditions dominated most of the stations across the main Hawaiian Islands during August 2023, July-August, June-August, and May-August. The last 5 to 12 months were mostly wetter than normal, except for the windward side of the Big Island and parts of Oahu and Maui. At longer time scales, windward sides of the islands were drier than normal and leeward sides wetter than normal, with a mixed pattern evident at 60 months (precipitation anomaly maps for the last 1, 2, 3, 4, 5, 6, 8, 9, 11, 12, 24, 36, 48, 60 months) (climate engine model percent of normal precipitation map for the last month).

Monthly streamflow was mostly below normal. Based on satellite analyses (stressed vegetation, drought stress, VHI), there were areas of vegetative stress this month on Oahu, Molokai, Maui, and the Big Island. Severe wildfires developed in August, especially on Maui.

Drought expanded across Hawaii during August, with the moderate to severe drought area increasing to cover 60.8% of the state on the August 29, 2023 USDM map, about ten times the value at the end of July.

Alaska

Alaska had a mixed precipitation anomaly pattern for much of the period, although certain areas stood out as dry at various times. The last 1 to 4 months were generally drier than normal in the panhandle and east-central interior regions, with some dryness in the southwest. Parts of the eastern interior region were dry at 5- to 11-month time scales, with dryness showing up along the southern coast, especially in the Cook Inlet and Northwest Gulf areas. Dryness was consistent in parts of the southern coast at longer time scales (low elevation station precipitation anomaly maps for the last 1, 2, 3, 4, 5, 6, 8, 9, 11, 12, 24, 36, 48, 60 months) (high elevation SNOTEL station precipitation percentile maps for the last 1, 3, and 11 months) (SNOTEL basin and station percent of normal precipitation maps for the last 1, 3, and 11 months) (climate division precipitation rank maps for the last 1, 3, 6, 8, and 12 months) (climate engine model percent of normal precipitation map for the last month) (Leaky Bucket model precipitation percentile map).

August 2023 temperatures were warmer than normal across the state, resulting in the third warmest August in the 1925-2023 statewide record, with near-normal temperatures at only a few stations in the Southwest. This temperature anomaly pattern held at the 2- to 4-month time scales, with the southwestern colder-than-normal area getting bigger at each time step. Colder-than-normal temperatures dominated in the west and interior regions, with above-normal temperatures in the east, north, and southeast, at 8 to 12 months when compared to more recent (1991-2020) normals. But when compared to the long-term (1926-2022) average, temperatures were near average in the west at 6-8 months and mostly warmer than average at 12 months. This is due to a pronounced warming trend in recent decades (low elevation station temperature anomaly maps for the last 1, 2, 3, 4, 8, 11, 12 months) (climate division temperature rank maps for the last 1, 3, 6, 8, and 12 months) (gridded temperature percentile maps for the last 1, 3, and 8 months) (Leaky Bucket model temperature percentile map).

Monthly streamflow was mostly near to above normal. Satellite observations of vegetative health (stressed vegetation, drought stress, VHI) revealed some areas of minor stress. Satellite-based observations of groundwater and soil moisture (GRACE root zone, GRACE surface, SMOS soil moisture, Leaky Bucket modeled soil moisture, SPoRT model soil moisture at shallow [0-10 cm, 10-40 cm] and deeper [40-100 cm, 100-200 cm] layers) suggested some dryness was occurring in the south and east. Numerous wildfires burned in central to east-central Alaska during August (wildfire maps for August 9, 14, 28, 31). Across the border in Canada, much of Yukon was ablaze.

The spots of moderate drought disappeared during August, with the area of abnormal dryness shrinking slightly to about 6.6% of the state on the August 29, 2023 USDM map.

Puerto Rico and U.S. Virgin Islands

August 2023 was drier than normal across the U.S. Virgin Islands (USVI) and northern parts of Puerto Rico (PR). The last 2-9 months were generally drier than normal in northern and central portions of PR, with wetter-than-normal conditions dominating at 12 months. The USVI were generally drier than normal for the last 2-12 months. Drier-than-normal conditions dominated at longer time scales and became progressively more widespread (radar-based precipitation anomaly estimates for the last 1, 2, 3, 6, and 8 months) (low elevation station precipitation anomaly maps for the last 1, 2, 3, 4, 5, 6, 8, 9, 11, 12, 24, 36, 48, 60 months) (climate engine model percent of normal precipitation map for the last month: PR and USVI, Caribbean and Gulf of Mexico region).

In a 64-year record, Rohlsen Airport on St. Croix had the third driest July-August and fifth driest February-August. In a 59-year record, King Airport on St. Thomas had the third driest December-August, fourth driest February-August, fourth driest April-August, fourth driest May-August, fifth driest June-August, and fifth driest July-August. In all of these rankings, years with too many days missing were excluded.

Temperatures were consistently warmer than normal, especially for the last 1 to 4 months (low elevation station temperature anomaly maps for the last 1, 2, 3, 4, 8, 11, 12 months). San Juan had the warmest August and second warmest July-August, and tied with 1980 for the warmest summer (June-August). Rohlsen Airport had the warmest August, second warmest July-August, and third warmest summer. King Airport recorded the third warmest August and July-August, and sixth warmest summer. The excessive heat increased evapotranspiration which made the dry conditions worse.

Root zone analyses indicated that soil conditions were moist across eastern coastal and portions of western PR, but dry along the southern and northern coasts (root zone soil saturation fraction). Satellite observations of vegetative health (stressed vegetation for PR and USVI, drought stress for PR and USVI, VHI for PR and USVI) revealed some areas of drought-related stress, especially on St. Thomas. Monthly streamflow on PR showed below-normal streams in western and eastern areas. In the USVI, the groundwater level fluctuated up and down during August. The net result for August was a decline at St. Croix, no change at St. John, and an increase at St. Thomas. For the most part, groundwater levels have been declining since the beginning of the year. The end-of-August groundwater level was well into the bottom third of the historical record on St. Croix and St. John, and mid-range on St. Thomas.

As reported by NIDIS (National Integrated Drought Information System), farmers and ranchers in the USVI have reported dry soils and vegetation stress. The combination of dry conditions, reduced access to good grazing, and heat stress has led to livestock losses. Poultry farmers report a continued decrease in egg production. The Virgin Islands Department of Agriculture on St. Croix reported that they provided more than 1,291,180 gallons of water to farmers in June; 1,020,050 gallons in July; and 903,930 gallons in August.

In the USVI, drought conditions remained unchanged with extreme drought on St. Croix and St. Thomas, and moderate drought on St. John. Severe drought ended on PR, with moderate drought shrinking slightly to cover about 8.3% of the island on the August 29, 2023 USDM map.

CONUS State Precipitation Ranks

August 2023 was drier than normal across the Southwest and Southern Plains to Florida, the Pacific Northwest coast, the Upper Midwest, and parts of the Mid-Atlantic, with record dryness occurring in parts of the southern Plains and Gulf Coast. Eleven states had a precipitation rank in the driest third of the 129-year historical record for August, including three that ranked in the top ten driest category — Louisiana (driest on record), Mississippi (fifth driest), and Texas (eighth driest).

The summer (June-August 2023) was drier than normal across the Southwest to Lower Mississippi Valley, much of the Pacific Northwest and California coast, the Upper Midwest, and parts of the Mid-Atlantic, with record dryness occurring in parts of the Southwest, southern Plains, Gulf Coast, and Upper Midwest. Eight states had a precipitation rank in the driest third of the 1895-2023 historical record for June-August, including six that ranked in the top ten driest category — Louisiana and New Mexico (both third driest), Minnesota and Wisconsin (both fifth driest), Texas (seventh driest), and Arizona (tenth driest).

March-August 2023 was drier than normal in much of the same places — across the Southwest to Lower Mississippi Valley, parts of the Pacific Northwest, much of the Upper Midwest, and parts of the Mid-Atlantic — with record dryness occurring locally in the Lower Mississippi Valley. Thirteen states had a precipitation rank in the driest third of the historical record for March-August, including four that ranked in the top ten driest category — Iowa (seventh driest), Minnesota (eighth driest), Louisiana (ninth driest), and New Mexico (tenth driest).

The dry areas persisted to the year to date. January-August 2023 was drier than normal across the Southwest to Gulf Coast, much of the Pacific Northwest, much of the Midwest into the central Plains, and parts of the Mid-Atlantic, with record dryness occurring locally in the Lower Mississippi Valley. Twelve states had a precipitation rank in the driest third of the historical record for January-August, including one that ranked in the top ten driest category — Maryland (ninth driest) — and two that were close: Washington (12th driest) and New Mexico (13th driest).

The dry pattern persisted through the last 12 months. September 2022-August 2023 was drier than normal across the Southwest to Gulf Coast, much of the Pacific Northwest, most of the Midwest into the adjacent central and northern Plains, and parts of the Mid-Atlantic. Fourteen states had a precipitation rank in the driest third of the historical record. None ranked in the top ten driest category, but three were close — Minnesota (12th driest), Iowa (13th driest), and Washington (13th driest).

Agricultural Belts

During August 2023, the Primary Corn and Soybean agricultural belt was drier and warmer than normal in northwest portions but wetter and cooler than average to the east and south. The month ranked as the 46th wettest and 44th warmest August, regionwide, in the 1895-2023 record.

March marks the beginning of the growing season for the Primary Corn and Soybean agricultural belt. March-August 2023 was mostly near to warmer than average with drier-than-normal conditions to the north and west and near- to wetter-than-normal conditions to the south and east. The period ranked as the 24th driest and 47th warmest March-August, regionwide.

The period April-June was especially dry for the Primary Corn and Soybean belt with temperatures mostly near to warmer than normal. Beneficial July and August precipitation in eastern and southern parts helped a little to improve longer-term (April-August) moisture deficits. April-August 2023 ranked as the 14th driest and 43rd warmest April-August, regionwide.

According to the U.S. Department of Agriculture (USDA), as of August 29, 2023, drought affected approximately 33% of barley production, 45% of corn production, 37% of cotton production, 58% of sorghum production, 40% of soybean production, 57% of spring wheat production, 46% of winter wheat production, 34% of hay acreage, 40% of the cattle inventory, 32% of the milk cow inventory, and 33% of the sheep inventory. The corn and soybean percentages improved from last month, but the rest mostly increased. Based on August 27 USDA statistics, 17% of the nation's corn crop, 14% of the soybean crop, 44% of the cotton crop, 24% of the spring wheat crop, and 37% of the nation's pasture and rangeland were in poor to very poor condition, and 52% of the nation's topsoil and 54% of the subsoil were short or very short of moisture (dry or very dry). During the first week of September, soil moisture conditions have gotten worse, with 58% of the nation's topsoil and 57% of the subsoil short or very short of moisture. The table below lists the end-of-August soil moisture, pasture and rangeland, corn, soybean, and spring wheat condition by state, with those states having 30 percent or more of topsoil or subsoil moisture short or very short, or 30 percent or more of the crop or pasture and rangeland in poor or very poor condition, highlighted in yellow:

Statewide topsoil moisture, subsoil moisture, and crop condition table

U.S.-Affiliated Pacific Islands

The NOAA National Weather Service (NWS) offices, the Pacific ENSO Applications Climate Center (PEAC), and partners provided reports on conditions across the Pacific Islands.

In the U.S. Affiliated Pacific Islands (USAPI) (maps — Federated States of Micronesia [FSM], Northern Mariana Islands, Marshall Islands [RMI], Republic of Palau [ROP], American Samoa, basinwide), August 2023 was drier than normal in the Marshall Islands, American Samoa, and Lukunor in the FSM, but near to wetter than normal in most other areas.

Monthly precipitation amounts were below the monthly minimum needed to meet most water needs (4 inches in the Marianas and Pago Pago, and 8 inches elsewhere) at Pingelap (FSM), Pago Pago (American Samoa), and Jaluit, Kwajalein, and Wotje (Marshalls). August precipitation was above the monthly minimums at the rest of the stations across the USAPI. The 4- and 8-inch thresholds are important because, if monthly precipitation falls below the threshold, then water shortages or drought become a concern.

The tropical Pacific climatology can experience extremes in precipitation, from very low precipitation during the dry season to very high precipitation during the wet season. This can result in monthly normal precipitation values that are different from the monthly minimum needed to meet most water needs, and this can lead to percent of normal values that seem odd. This was the case during August 2023, which is in the wet season for most of Micronesia, and in the dry season for American Samoa and Kapingamarangi.

Precipitation was above the monthly minimum but below normal (1981-2010 normal), because the normals are high, at:

  • Kapingamarangi: August 2023 precipitation 9.87 inches, August normal mean 10.51 inches, August normal median 8.13 inches.
  • Majuro: August 2023 precipitation 11.07 inches, August normal mean 11.42 inches, August normal median 11.69 inches.
  • Lukunor: August 2023 precipitation 10.33 inches, August normal mean 14.18 inches, August normal median 14.04 inches.

In the table below, the station identified as Koror is Palau International Airport (Airai).

Pacific Island Percent of 1981-2010 Normal Median Precipitation
Station Name Sep
2022
Oct
2022
Nov
2022
Dec
2022
Jan
2023
Feb
2023
Mar
2023
Apr
2023
May
2023
Jun
2023
Jul
2023
Aug
2023
Sep-
Aug
Chuuk121%124%93%116%92%215%85%137%191%118%130%118%122%
Guam NAS109%150%77%182%350%188%263%198%916%146%86%132%146%
Kapingamarangi44%34%55%53%166%47%116%141%137%145%162%121%95%
Koror45%241%88%105%187%102%185%77%165%77%145%125%117%
Kosrae134%169%107%99%131%188%67%120%87%166%132%104%103%
Kwajalein68%161%81%88%224%50%189%188%345%143%45%81%120%
Lukonor36%95%94%54%124%68%96%77%61%116%75%74%70%
Majuro159%147%91%90%157%138%169%151%102%105%70%95%117%
Pago Pago60%149%118%71%114%110%106%152%168%109%102%42%98%
Pohnpei143%148%85%74%136%146%109%141%145%121%148%219%131%
Saipan67%151%60%130%441%118%138%192%225%92%46%142%120%
Yap57%217%68%131%133%118%137%104%131%121%168%145%125%
Pacific Island Precipitation (Inches)
Station Name Sep
2022
Oct
2022
Nov
2022
Dec
2022
Jan
2023
Feb
2023
Mar
2023
Apr
2023
May
2023
Jun
2023
Jul
2023
Aug
2023
Sep-
Aug
Chuuk14.15"14.27"9.83"13.00"9.34"15.60"7.09"17.14"21.57"13.73"15.56"15.23"166.51"
Guam NAS13.74"17.12"5.66"9.32"14.02"5.69"5.45"5.01"31.15"9.00"8.69"19.47"144.32"
Kapingamarangi4.38"2.76"5.11"5.23"15.23"4.37"13.24"19.19"16.59"20.04"22.86"9.87"138.87"
Koror5.26"28.49"10.00"11.76"19.04"8.74"13.74"5.60"19.53"13.44"26.81"16.86"179.27"
Kosrae19.11"18.53"14.74"15.95"21.87"24.25"10.81"21.08"15.41"24.30"19.67"14.72"220.44"
Kwajalein7.34"18.02"9.09"5.88"7.08"1.32"4.43"9.87"23.18"9.93"4.45"7.86"108.45"
Lukonor3.70"10.73"8.52"6.06"10.45"6.08"8.92"8.68"7.13"13.55"11.89"10.33"106.04"
Majuro17.72"18.76"12.21"10.30"12.14"9.51"11.12"14.23"10.35"11.56"7.87"11.07"146.84"
Pago Pago3.92"13.82"11.93"9.10"15.19"13.19"11.34"14.25"16.19"5.81"5.64"2.26"122.64"
Pohnpei17.91"22.62"12.66"11.86"17.94"13.99"14.29"25.90"29.02"17.94"22.76"31.21"238.1"
Saipan6.72"16.07"3.39"5.01"11.16"3.05"2.61"5.05"5.35"3.34"4.13"18.62"84.5"
Yap7.76"26.48"5.99"11.17"8.51"6.11"6.26"5.86"10.28"14.59"25.35"21.43"149.79"
Pacific Island 1981-2010 Normal Median Precipitation (Inches)
Station Name Sep
2022
Oct
2022
Nov
2022
Dec
2022
Jan
2023
Feb
2023
Mar
2023
Apr
2023
May
2023
Jun
2023
Jul
2023
Aug
2023
Sep-
Aug
Chuuk11.71"11.51"10.61"11.25"10.10"7.25"8.32"12.47"11.30"11.66"11.98"12.86"136.77"
Guam NAS12.66"11.44"7.38"5.11"4.01"3.03"2.07"2.53"3.40"6.18"10.14"14.74"99.09"
Kapingamarangi9.93"8.19"9.27"9.84"9.15"9.27"11.43"13.64"12.08"13.78"14.15"8.13"145.85"
Koror11.77"11.84"11.39"11.16"10.18"8.56"7.44"7.32"11.83"17.48"18.53"13.50"152.90"
Kosrae14.22"10.94"13.83"16.11"16.67"12.93"16.06"17.51"17.75"14.64"14.91"14.22"213.87"
Kwajalein10.74"11.18"11.28"6.66"3.16"2.64"2.35"5.26"6.72"6.93"9.87"9.74"90.41"
Lukonor10.15"11.32"9.08"11.27"8.41"8.93"9.26"11.31"11.69"11.65"15.93"14.04"151.36"
Majuro11.17"12.73"13.44"11.39"7.74"6.88"6.58"9.42"10.11"11.01"11.17"11.69"125.25"
Pago Pago6.53"9.26"10.14"12.84"13.34"12.00"10.68"9.39"9.66"5.33"5.55"5.38"125.57"
Pohnpei12.55"15.27"14.83"16.08"13.18"9.55"13.17"18.41"19.96"14.81"15.43"14.26"182.36"
Saipan10.09"10.62"5.61"3.85"2.53"2.59"1.89"2.63"2.38"3.62"8.91"13.13"70.25"
Yap13.50"12.18"8.83"8.51"6.39"5.19"4.56"5.63"7.85"12.04"15.08"14.82"120.31"

As measured by percent of normal precipitation, Lukunor was drier than normal in the short term (August and the last 3 months [June-August]) and long term (year to date [January-August] and last 12 months [September 2022-August 2023]). Pago Pago was drier than normal in the short term and near to below normal in the long-term. Kwajalein and Majuro were drier than normal in the short term but wetter than normal in the long term. Kapingamarangi was drier than normal at the 12-month time scale, but wetter than normal for the other 3 time scales. Airai, Chuuk, Guam, Kosrae, Pohnpei, Saipan, and Yap were near to wetter than normal for all 4 time periods.

Based on percent of normal average (instead of normal median values), in the Marianas Islands, August was mostly wetter than normal across the main islands, but the last 2 to 3 months had drier-than-normal conditions at several stations. It was predominantly wetter than normal across the main islands at the 4- to 24-month time scales, with some dryness showing up on Saipan at longer time periods (percent of normal precipitation maps for the last 1, 2, 3, 4, 5, 6, 8, 9, 11, 12, 24, 36, 48, 60 months).

Based on percent of normal average (instead of normal median values), in the Marshall Islands, the last 1 to 4 months were drier than normal across most of the islands. The last 5 to 24 months were drier than normal at Jaluit but wetter than normal at the other primary stations. Longer time periods were drier than normal in the southwest (Jaluit) and north (percent of normal precipitation maps for the last 1, 2, 3, 4, 5, 6, 8, 9, 11, 12, 24, 36, 48, 60 months).

According to the August 31 USDM produced for the USAPI, Tutuila (Amerian Samoa) and Wotje (RMI) were in moderate drought, Kwajalein (RMI) and Pingelap (FSM) were abnormally dry, and the rest of the USAPI stations were free of drought and abnormal dryness. The reservoir level on Majuro began the month at a low level (28.5 million gallons), held fairly steady for the next 2 weeks before reaching a low value of 26.7 million gallons on the 19th, then steadily rose to a peak of 31.9 million gallons by the end of the month. The threshold of concern for drought is usually 28.8 million gallons, but for the past several months, one sector of the reservoir has been serviced. This portion of the reservoir system typically holds 8 million gallons, so the threshold reservoir level is lower than it normally would be. The minimum value reached during this month was above the new threshold for concern. Satellite observations of vegetative health (drought stress, stressed vegetation, VHI) indicated there were some areas of stressed vegetation on Guam, but little concern for drought.

August 2023 precipitation ranks ranged from very dry to very wet and everything in between, based on data available at the time of this report. Lukunor, Pago Pago, and Pingelap had August precipitation that ranked in the top ten driest category, while Kapingamarangi, Mili, Nukuoro, Pohnpei, Saipan, Ulithi, and Yap ranked in the top ten wettest category:

  • Pago Pago: sixth driest August (in a 58-year record).
  • Lukunor: ninth driest August (27 years) and third driest September-August.
  • Pingelap: seventh driest August (39 years) and sixth driest July-August and June-August.
  • Kwajalein: 27th driest August (72 years) but fifth driest July-August.
  • Jaluit: 14th driest August (40 years) but fourth driest July-August and sixth driest September-August.

Some stations at the wet end of the scale:

  • Ulithi had the second wettest August (41 years) and wettest June-August and May-August.
  • Yap ranked ninth wettest for August (73 years) and wettest for July-August and October-August.
  • Pohnpei had the second wettest August (73 years) and wettest July-August and June-August.
  • Mili had the second wettest August (39 years) and wettest July-August through May-August, and wettest January-August through September-August.

The following analysis of historical data for the USAPI stations in the Global Historical Climatology Network-Daily (GHCN-D) dataset, augmented with fill-in data from the 1981-2010 Normals, helps put the current data into historical perspective by computing ranks based on the period of record. The table below lists the precipitation ranks for August 2023, March-August 2023 (last 6 months), and September 2022-August 2023 (the last 12 months). Some stations have a long period of record and their dataset is fairly complete, while other stations have a shorter period of record and the dataset has some missing data.

August 2023 USAPI Precipitation Ranks (1 = driest)
StationAugust 2023Mar-Aug 2023Sep 2022-Aug 2023Period of Record
RankYearsRankYearsRankYears
Ailinglaplap2939353931371981-2023
Airai4972637166711951-2023
Chuuk5273637265721951-2023
Fananu37--3--32003-2023
Guam4867656765661957-2023
Jaluit14405396371981-2023
Kapingamarangi2533242611211962-2023
Kosrae3255234522351954-2023
Kwajalein2772527151711952-2023
Lukunor9277273261981-2023
Majuro3370366951691954-2023
Mili3839363835351981-2023
Nukuoro3240243933381981-2023
Pago Pago658325725571966-2023
Pingelap7391938--341981-2023
Pohnpei7273697269721951-2023
Saipan3943364232341981-2023
Ulithi4041363833351981-2023
Utirik--16--7--41985-2020
Woleai2142--33--281968-2023
Wotje1540303927361981-2023
Yap6573677267721951-2023
Map of USAPIAugust 2023 Precipitation (Inches)
Map of USAPI August 2023 Percent of Normal Precipitation
Map of USAPI June 2023-August 2023 Percent of Normal Precipitation
Map of USAPI January-August 2023 Percent of Normal Precipitation
Map of USAPI September 2022-August 2023 Percent of Normal Precipitation

SPI values for seven time periods for Pacific Islands, computed by the Honolulu NWS office.

SPI values for seven time periods for Pacific Islands

NOAA Regional Climate Centers

More information, provided by the NOAA Regional Climate Centers and others, can be found below.

Southeast

As noted by the Southeast Regional Climate Center, mean temperatures were above average across much of the Southeast region in August. The greatest departures were found across southern portions of Alabama and Georgia, the northern half of Florida, and Puerto Rico and the U.S. Virgin Islands, where temperatures were 2 to 4 degrees F (1.1 to 2.2 degrees C) above average for the month, with some locations running up to 6 degrees F (3.4 degrees C) above average. For the second straight month, several locations recorded their warmest month on record, including Mobile, AL (1871-2023), Pensacola, FL (1897-2023), Tallahassee, FL (1896-2023), Daytona Beach, FL (1923-2023), Orlando, FL (1892-2023), Tampa, FL (1890-2023), Miami, FL (1895-2023), and Rohlsen Airport on the island of Saint Croix (1951-2023). Fort Myers, FL (1902-2023), Charleston, SC (1938-2023), Brunswick, GA (1948-2023), and San Juan, PR (1898-2023) all recorded their warmest August on record.

As has been the case for the past several months, precipitation was highly variable across the Southeast in August. The wettest locations were found across northern portions of Alabama and Georgia, western North Carolina, southern Virginia, and coastal sections of Georgia and the Carolinas. In contrast, the driest locations were found across southern portions of Alabama, northwest Florida, central Florida, and northern Virginia, where monthly precipitation was less than half of the expected amount. Pensacola, FL recorded 2.52 inches (64 mm) of precipitation, which is nearly 5 inches (127 mm) below average for the month. Charlottesville, VA recorded just 0.86 inch (22 mm) of precipitation in August, which is only 22 percent of normal. Precipitation in August was below average across Puerto Rico, except for some interior locations, and below average across the U.S. Virgin Islands.

At the start of the month, about 11 percent of the region was dry or in drought according to the USDM. Small areas of abnormal dryness (D0) or moderate (D1) drought were eliminated across northern sections of Alabama, Georgia, and South Carolina. Severe (D2) and extreme (D3) drought persisted across the West Coast of Florida, particularly in Manatee and Sarasota counties. Moderate (D1) drought emerged across the western Panhandle of Florida, while severe (D2) drought emerged across parts of southern Alabama. Abnormal dryness (D0) expanded across central and eastern sections of the Carolinas along with the emergence of small pockets of moderate (D1) drought. Drought conditions worsened across northern Virginia, with a small area of severe (D2) drought emerging by the end of the month. Overall, about 30 percent of the region was dry or in drought by the end of August. In the Caribbean, drought conditions improved across Puerto Rico. The area of severe (D2) drought on the northwest part of the island improved to moderate (D1) drought, while abnormal dryness (D0) was eliminated across the eastern half of the island and on the outlying islands. Conditions on Saint John improved from severe (D2) to moderate (D1) drought, while extreme (D3) drought persisted on Saint Thomas and Saint Croix.

The heat and lack of rain resulted in reports of crop damage. Wilting was observed on cotton, peanuts, and soybeans. As this is the time of year when water demand is highest, declines in soil moisture could limit their growth and yield potential. Apple orchards in Virginia reported premature ripening and smaller sizes due to the lack of rain, which is causing the apples to fall before picking season begins. Livestock and pastures were in mostly fair to good condition, though operators continued to note cases of heat stress and some pastures were turning brown due to the heat and lack of rain. Hot and dry weather continued to impact farming and ranching across the Caribbean. Many crops exhibited delayed growth, and a lack of soil moisture made it difficult to harvest and plant new crops. Work schedules for farmers had to be altered due to extreme temperatures. Dry conditions have led to significant feed shortages, while farmers continued to report losses to livestock and declines in egg production due to the heat.

South

As explained by the Southern Regional Climate Center, heat and drought affected much of the Southern region in August, setting many records across Texas, Louisiana, and Mississippi. Above-normal temperatures were prevalent across wide swaths of the Southern region, especially across Texas, Louisiana, and southern Mississippi where temperatures were six to ten degrees above normal for August. Louisiana (1st) and Mississippi (1st) both experienced their hottest Augusts on record, running 5.7 F and 4.1 F above their 1991-2020 normals. Texas (2nd) and the Southern region (2nd) as a whole had their second hottest August on record.

Precipitation was below normal for much of the Southern region during August except for much of Tennessee, northern Arkansas, and deep south Texas. State totals were extremely low for Louisiana, which experienced its driest August on record with 1.27 inches of precipitation vs. the 1991-2020 normal of 5.1 inches. Also very dry were Mississippi (5th driest) and Texas (8th driest). The Southern region as whole (16th driest) and Oklahoma (42nd driest) were drier than normal as well.

During August the Southern region saw degradation of drought conditions across a majority of the region, the exceptions being northern Oklahoma, northern Arkansas, and isolated areas of Tennessee and deep south Texas. As of August 29th, northern Oklahoma, most of Arkansas, northern Mississippi, and much of Tennessee remained drought free. Extreme and exceptional drought, according to the USDM, expanded significantly across the region during August with much of that expansion occurring from central Texas across through coastal Mississippi. As of August 29th, 56 percent of the Southern region was in some level of drought, with 25 percent of that being Extreme and 8 percent being Exceptional. Drought conditions, exacerbated by record-hot temperatures, have led to short to very short topsoil moisture conditions across much of the Southern region, the exception being Tennessee. The hot and dry conditions have particularly impacted the cotton crops in Oklahoma and Texas, with both states reporting only eleven percent of cotton crops being rated as Good to Excellent by the USDA as of September 3rd. Dry and hot conditions have led to burn bans, water restrictions, and low streamflow in many areas affected by drought. In the Highland Lakes in Texas, the lowest inflows on record were recorded in August, with records dating back to 1942. Rangeland and pasture conditions in the western portions of the region continue to suffer, and there are increasing reports of ranchers reducing the size of their herds due to feed and water limitations.

Midwest

As described by the Midwest Regional Climate Center, the average August temperature for the Midwest was 71.1 degrees F (21.7 degrees C), which was 0.2 degrees F (0.1 degrees C) above the 1991-2020 normal, and the average summer (June-August) temperature for the Midwest was near normal, with slightly above-normal temperatures in the west and slightly below-normal temperatures in the east. An unusually strong, long-lasting upper atmospheric heat dome trapped a hot and humid air mass across the lower Midwest from August 19-25. Triple-digit heat index values were paired with excessively warm overnight temperatures, prompting the National Weather Service to issue widespread excessive heat warnings across most of the Midwest. August precipitation totaled 4.02 inches (102 mm) for the Midwest, which was 0.35 inch (9 mm) above normal, or 109 percent of normal. Precipitation was 25-75 percent of normal in the northwestern portion of the region, with precipitation near or above normal in the southern and eastern portions of the region. Summer (June-August) precipitation for the Midwest totaled 10.47 inches (266 mm), which was 1.84 inches (46.7 mm) below normal. Summer precipitation deficits of 4-10 inches (101.6-254 mm) were widespread across the northwest, while precipitation surpluses of 2-8 inches (50.8-203.2 mm) were observed across the south-central and eastern Midwest.

Throughout August, drought conditions improved in the east, with abnormal dryness and drought significantly reduced or eliminated in Illinois, Indiana, Kentucky, Michigan, and Ohio. Conversely, drought expanded and intensified in the northern and western portions of the region. By month's end, about 41 percent of the Midwest was in drought, according to the USDM, with the most dire conditions in the Upper Mississippi River Basin. Wisconsin reached a Drought Severity Coverage Index (DSCI) of 248 in late August, which tied for the highest DSCI since those records began in 2000. Drought in the northwest intensified rapidly over the last 12 weeks since the start of summer when the Upper Mississippi River Basin was either abnormally dry or drought-free. By late August, the ongoing summer drought resulted in low flows and navigation restrictions on the Mississippi River, reduced corn and soybean yields, and increased wildfire risk.

Northeast

As summarized by the Northeast Regional Climate Center, much of the Northeast experienced a cool, soggy August. The Northeast's average temperature for August was 67.7 degrees F, 1.0 degree F cooler than normal, and the summer average temperature was 67.8 degrees F, 0.3 degrees F cooler than normal. The Northeast had its 12th wettest August on record, picking up 5.25 inches of precipitation, 130 percent of normal, and third wettest summer since recordkeeping began with 16.26 inches of precipitation, 127 percent of normal.

The USDM from August 1 showed 1 percent of the Northeast in severe drought, 3 percent in moderate drought, and 11 percent as abnormally dry. Sufficient precipitation fell to allow drought and abnormal dryness to contract in multiple areas, particularly New York and the northern half of Pennsylvania. Also, severe drought eased in central Maryland. However, drier conditions prevailed in several areas, especially eastern West Virginia where moderate drought was introduced and abnormal dryness expanded. The USDM from August 29 showed 2 percent of the Northeast in moderate drought and 9 percent as abnormally dry. A few locations such as central Maryland, south-central Pennsylvania, central/coastal New Jersey, and eastern West Virginia experienced much below normal streamflow and/or groundwater levels at times during August. USGS 7-day average streamflow was much below normal or lower for areas such as central Maryland, south-central Pennsylvania, eastern West Virginia, and southern New Jersey. Groundwater levels reached record low levels at times during August in some of these same areas. In late August, at least 17 public water suppliers in Pennsylvania, most in the southeastern part of the state, were requesting that customers voluntarily conserve water. In late August, daily drought monitoring resumed along the Potomac River, which supplies portions of the Mid-Atlantic including much of the Washington, D.C., metro area with water.

High Plains

As summarized by the High Plains Regional Climate Center, August ended with a bang, after one of the more significant heatwaves impacted parts of the region in the final days of the month. Warmer temperatures dominated much of the region but were not record-breaking despite the intense heatwave. Large portions of the region observed 2 to 4 degrees F (1.1 to 2.2 degrees C) above normal temperature, while only a few isolated locations reporting below-normal temperatures. All walks of daily life were impacted by the historic heatwave near the end of the month. Crops were burnt to a crisp, all but sealing the fate of an already poor crop for some. Hundreds of cattle reportedly perished in Kansas and Nebraska after the heat index surpassed 120 degrees F (49 degrees C) for multiple days. Manhattan, Kansas hit 115 degrees F (46 degrees C) on the 19th, beginning one of the warmest weeks for the city. From the 19th to the 25th, the average high temperature was 108.3 degrees F (42.4 degrees C). This put a serious strain on utility providers, as the extended period of heat forced people to use air-conditioning longer than usual to cool their homes.

The western parts of the region continued the summertime trend of above-normal precipitation. Some areas in the Dakotas and Wyoming received record to near-record precipitation, which eliminated drought conditions. While much of Colorado had abundant precipitation, Alamosa had its driest summer with a meager 0.56 inch (1.42 cm).

Drought conditions improved across the central portions of the region but continued to degrade in North Dakota and southwestern Colorado. Overall, abnormally dry to exceptional drought (D0-D4) was reduced by nearly 7 percent in the High Plains. An unusual pattern this summer has led to high precipitation amounts in the western part of the region, with Wyoming benefiting the most. The entire state is drought-free for the first time since July of 2019. Kansas continued to improve, with a 10 percent reduction to extreme to exceptional drought (D3-D4) this month. Despite improvements this month, drought firmly remains entrenched in eastern Nebraska. Elsewhere in the region, other localized improvements and degradations were observed.

West

As summarized by the Western Regional Climate Center, much of California and the Great Basin had a rare wet August with monthly precipitation totals more than 300 percent of normal. The extreme rainfall event resulted from remnants of Hurricane Hilary being drawn northward and interacting with an area of low pressure off the coast of northern California that ejected to the northeast and entrained excessive moisture. Most of southern Arizona and New Mexico saw well below-normal precipitation which continued the trend of one of the driest monsoon seasons on record, with many locations receiving less than 50 percent of normal precipitation. Phoenix, Arizona logged just 0.12 inch of rain (13 percent of normal) and White Signal, New Mexico had its driest August in 50 years of records with 0.25 inch of rain (2.49 inches below normal). Temperatures were near-to-below normal across parts of southern California, Nevada, and western Utah and above normal elsewhere. Temperatures were 3-6 degrees Fahrenheit above normal across western Oregon and western Washington and many locations set records for the warmest August. After a record shattering July with extreme temperatures, the heat continued for Arizona and New Mexico throughout August.

According to the USDM at the end of August, 31 percent of the West was in drought. Drought conditions have worsened over Arizona, New Mexico, southwest Colorado, northern Montana, Washington, and parts of western Oregon. Extreme drought (D3) can be found in parts of northwest Washington, northwest Montana, and New Mexico. Remnants of Hurricane Hilary helped to erase remaining drought conditions in southeast California and southwest Nevada.

Alaska: Temperatures were 2-5 degrees Fahrenheit above normal across much of Alaska with the largest anomalies throughout the Interior. Precipitation was above normal across most of Alaska except for some isolated areas in the Interior, southwest Alaska, and the Panhandle. Anchorage recorded 3.83 inches of precipitation in August (131 percent of normal) and Nome logged 4.61 inches (143 percent of normal). Only 0.01 inch of precipitation fell at Northway, where the August normal is 1.79 inches, making it the driest August on record.

Hawaii: Precipitation was below normal across the region with many locations receiving less than 50 percent of normal for the month of August. On Maui, Hana recorded 1.88 inches of precipitation for the month (31 percent of normal) coming in as the fourth driest on record. Lihue, on the east coast of Kauai, measured 0.89 inch of precipitation for the month (38 percent of normal). On the Big Island Hilo logged 5.35 inches of precipitation at 47 percent of normal. Dryness led to drought expansions based on the USDM with 61 percent of Hawaii in drought at the end of August with three category degradations (no drought to D2) in parts of the Big Island. The entire west coast of Maui, including where the Lahaina fires occurred, was in severe drought (D2) at the end of August.

Additional Resources


Citing This Report

NOAA National Centers for Environmental Information, Monthly Drought Report for August 2023, published online September 2023, retrieved on March 5, 2024 from https://www.ncei.noaa.gov/access/monitoring/monthly-report/drought/202308.