Issued 14 September 2021

August 2021 Palmer Z-Index
U.S. Percent Area Wet or Dry January 1996 - August 2021
August 2021 /monitoring-content/sotc/drought/2021/08/ca-p-reg004dv00elem01-09082021.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

August 2021 began with an upper-level circulation pattern consisting of a strong long-wave ridge over the western CONUS and trough over the East. Shortwave troughs and ridges, as well as closed lows, migrated through the upper-level flow during the month. The alternating pattern of ridges and troughs flattened the jet stream flow when aggregated over the entire month. A cold front reached the Gulf of Mexico coast early in the month, but for the most part fronts and surface lows stayed across the northern tier states while high pressure tended to dominate across the southern tier states. The alternating and migratory nature of the circulation kept monthly temperatures near to cooler than normal in the northern Rockies and southern Plains. Anomalous ridging over eastern North America for much of the month contributed to warmer-than-normal monthly temperatures from the central and northern Plains to the Great Lakes, Northeast, and Mid-Atlantic states, while anomalous ridging over the eastern Pacific gave the West Coast warmer-than-normal monthly temperatures. When summed over the month, the migrating troughs and fronts generated above-normal precipitation across the Great Basin to northern Rockies and parts of the western Great Lakes, an active summer monsoon brought above-normal rainfall to parts of the Southwest, and tropical systems Fred, Henri, and Ida left above-normal precipitation in their wake from the Lower Mississippi Valley to the Northeast. Much of the West Coast to Great Basin and parts of the Plains and northern New England had a drier-than-normal month.

Drought conditions were reflected in low to record-low streamflow, low groundwater (USGS and GRACE satellite observations) and spring water levels, dry soil moisture (SMOS satellite observations; NESDIS satellite observations of moisture stress; SPoRT satellite-based observations for 0-10 cm [0-4 inches] depth, 0-40 cm [0-16 inches] depth, 0-100 cm [0-39 inches] depth, 0-200 cm [0-79 inches] depth; GRACE satellite-based observations for surface and root zone soil moisture; the USDA Crop Condition and Soil Moisture Analytics [CASMA] soil moisture anomaly for topsoil and subsoil, CASMA soil moisture category for topsoil and subsoil, and field observations of topsoil moisture; and CPC, Leaky Bucket, NLDAS, and VIC soil moisture models), stressed vegetation (satellite-based measures of vegetation health [NESDIS stressed vegetation, Vegetation Health Index (VHI), Vegetation Condition Index (VCI)]) and the VegDRI and QuickDRI products), low reservoir levels (California map, statewide summary, westwide map), and high evapotranspiration (EDDI maps for last 1, 2, 3, 4 months). These conditions were especially notable across the West, northern to central Plains, Northeast, Upper Mississippi Valley, and parts of Florida and the central Appalachians. The month began with several large wildfires occurring across the West and northern Plains, with high concentrations in the Pacific Northwest and along the West Coast; they mostly ended in the northern Plains by the end of the month (wildfire maps for August 1, 4, 9, 13, 17, 24, 26, 31), with total acreage burned for the year to date of about 4.9 million acres, which is below the ten-year average of 5.6 million acres. The total number of fires so far this year is 42,889, which is above the ten-year average.

Reports received through the Condition Monitoring Observer Reports (CMOR) system and via the National Drought Mitigation Center included continued drought impacts to farming and ranching operations (especially crop and livestock issues, lack of water, poor water quality, reduced yields), fire risk, lack of food and water for wildlife, dry lawns, and stress to people, mostly in the West and northern Plains, but also in some areas in the Midwest and East. In Minnesota, there is no hay or grazing for the livestock, so ranchers are being forced to sell cattle, but sale barns are not accepting livestock because there are no buyers. Ranchers across the continent are suffering: Extreme heat and drought have dried up pastures, leaving no hay or feed for cattle, pushing many cattle producers from Canada to Mexico to sell livestock. The liquidation of breeding stock is expected to limit cattle production for years, tighten the North American beef supply, and increase prices consumers will pay, according to ranchers and cattle experts. Some reservoirs in Minnesota were nearing the lows reached during the drought in 1988. The St. Cloud, MN Hydroelectric Generation Facility ceased production August 16 when the Mississippi River dropped below 700 cubic feet per second and was near a historical low. Power production has not ended due to low flows since 1988. The Piscataquis River in Dover-Foxcroft, Maine hit a historic low, while the St. John River in Aroostook was also near a record low. Low lake levels were affecting recreational activities in Arizona, Utah, and West Virginia. The town of Strasburg, Virginia declared a drought warning condition and encouraged water conservation as the flow in its river slowed. A Level 1 Shortage Condition was announced for Lake Mead. Under the shortage condition, Arizona will receive about 18% of the state's annual apportionment from the Colorado River, Nevada will receive 7%, and Mexico will receive about 5% of the country's annual allotment, effective January 1, 2022. The July runoff above the Fort Peck Dam in Montana was the lowest on record, due to drought and heat, according to the U.S. Army Corps of Engineers. This was affecting downstream navigation on the Missouri River, were navigation support will be maintained at an intermediate service level of 1,500 cubic feet per second below full-service levels through the end of the normal 8-month navigation flow support season. The power plant at Lake Oroville in northern California stopped generating electricity on August 5 as the lake reached a new record low and was at 24% of capacity. Dozens of communities are at risk of running out of water as wells go dry in northern California and southern Oregon. Groundwater was dropping to historical depths in Madera County, California amid the ongoing drought, causing subsidence. Lots of wells were running dry, and drillers were scheduled out for months as the county's water demand far exceeds supplies and recharge. California Governor Gavin Newsom stated that he may enact mandatory water restrictions in as soon as six weeks as drought intensified in the state, which would be early October. California's water year begins October 1. Gov. Newsom already requested a 15% voluntary conservation. The Metropolitan Water District (MWD) of Southern California issued a water supply alert signaling that conservation is needed as drought continues. The last time an official supply alert was issued was in 2014; such an alert is the third of four stages in the agencies' water supply framework. MWD serves 19 million people in six counties in Southern California, including the Los Angeles area. Drought is drying out and killing some trees and plants in Oregon's Willamette Valley, threatening the livelihood of tree farmers. Drought means fewer flowers producing nectar for bees to make honey, so bee populations and honey production were reduced in the northern Plains and Midwest.

As a result of these conditions, drought or abnormal dryness expanded or intensified in parts of the Pacific Northwest, northern and central Plains, Upper Mississippi Valley, Ohio Valley, Puerto Rico, and Hawaii. Beneficial rains caused drought or abnormal dryness to contract or decrease in intensity in the Southwest, Alaska, central and southern Appalachians, and parts of the northern Plains and Upper Mississippi Valley, and other parts of Hawaii and Puerto Rico. Drought expansion slightly exceeded contraction for the CONUS with the USDM-based national moderate-to-exceptional drought footprint increasing from 46.3 percent at the end of July to 46.6 percent at the end of August. For the 50 States and Puerto Rico, drought contraction exceeded expansion, with the drought footprint falling from 40.0 percent to 39.0 percent. According to the Palmer Drought Index, which goes back to the beginning of the 20th century, about 42.8 percent of the CONUS was in moderate to extreme drought at the end of August, about the same when compared to the end of July. The percent area of the CONUS in moderate to extreme drought has hovered between 35 and 48 percent for the last 12 months (since September 2020).

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Drought conditions at the end of August, as depicted on the August 31, 2021 USDM map, included the following core drought and abnormally dry areas:

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 2021 Palmer Z-Index
August 2021 PHDI

Used together, the Palmer Z Index and PHDI maps show that short-term drought occurred across the Far West, the foothills of the Rockies and parts of the central and northern Plains, and northern portions of Minnesota, Wisconsin, Michigan, and New England. In these areas, long-term drought continued, intensified, or expanded (PHDI maps for August compared to July). Short-term wet conditions in parts of the Southwest and southern portions of the Upper Mississippi Valley contributed to contraction of long-term drought or reduction in its intensity. Short-term wet conditions across the southern Plains to southern Appalachians, and from the central Appalachians to southern portions of the Great Lakes and Northeast, led to expansion, intensification, or introduction of long-term wet conditions.

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 2021 SPI
July-August 2021 SPI
June-August 2021 SPI
March-August 2021 SPI

The SPI maps illustrate how moisture conditions have varied considerably through time and space over the last two years. In the West, dry conditions are evident in some areas at the 1-month time scale, across the Far West at 2 months, the northern and far western sections at 3 months, across the West (except for the Southwest) at 6 and 9 months, and across all or most of the West at 12 and 24 months. The central High Plains are dry at 1-3 months. Parts of the northern Plains are dry at 2 months, with dryness widespread across the central and northern Plains at 3 months, and across the northern Plains to Upper Mississippi Valley at 2 to 12 months. Northern Maine is dry at all time scales, with dryness in northern Vermont and New Hampshire at 6-9 months. The central Appalachians to Carolina coast has dryness at 6 months, while southern Florida shows up dry at 6-9 months. This year's summer monsoon has given parts of the Southwest wet SPI values from 1 to 9 months. Wet conditions dominate much of the Gulf of Mexico coast and parts to much of the Northeast at all time scales, much of the Ohio Valley at 2-6 and 24 months, and the Mid-Mississippi Valley at 2-24 months. An interesting pattern is evident at the 12- and 24-month time scales — very dry conditions dominate across the West to northern Plains, while very wet conditions dominate the Deep South to mid-Atlantic Coast.

December 2020-August 2021 SPI
September 2020-August 2021 SPI
September 2019-August 2021 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 warmest season of the year (when evapotranspiration reaches its annual maximum). During August 2021, temperatures were above normal across the Far West, Great Lakes to Northeast, and parts of the Southwest, resulting in increased evapotranspiration. This led to a more severe SPEI than SPI where precipitation was below normal. For the summer (June-August 2021), record to near-record hot temperatures occurred across a large part of the West and northern Minnesota. The increased evapotranspiration contributed to SPEI values that far exceeded the corresponding SPI values. This was the case for much of the past year (SPEI maps for last 1, 2, 3, 4, 5, 6, 9, 12 months) (SPI maps for last 1, 2, 3, 4, 5, 6, 9, 12 months), especially over the West and northern Plains.

The SPEI was record dry for several states for several of the time periods over the last one to 12 months. In many cases, the corresponding SPI was not record dry:

  • California (SPEI for last 3, 4, 5, 6, 7, 9, 10, 11, 12 months) (SPI for last 3, 5, 7, 10, 11, 12 months)
  • Oregon (SPEI for last 3, 4, 5, 6 months) (SPI for last 5, 6 months)
  • Washington (SPEI for last 5 and 6 months) (SPI for last 5 and 6 months)

Temperatures have been much warmer than normal in the West for much of the last one to eight years. The excessive evapotranspiration, especially during the warm season, has contributed to more extreme SPEI values than SPI values for much of this period (SPEI maps for the last 12, 24, 36, 48, 60, 72 months) (SPI maps for the last 12, 24, 36, 48, 60, 72 months).

The above-normal Southwest monsoon rains of the last two months have helped make up deficits in the short term, but significant long-term deficits still remain. Many multi-year SPEI values, and some multi-year SPI values, are still record dry for several states:

  • Arizona (SPEI for last 48, 72 months) (SPI for last 48, 72 months)
  • California (SPEI for last 12, 15, 18, 24 months) (SPI for last 12, 15, 24 months)
  • Nevada (SPEI for last 18 and 24 months) (SPI for last 18 and 24 months)
  • Oregon (SPEI for last 15 and 18 months)

Regional Discussion

Hawaii

August 2021 had a mixed precipitation anomaly pattern across Hawaii. But with dry conditions occurring during several previous months, July-August, June-August, May-August, and April-August 2021 were drier than normal across the main Hawaiian Islands, except for some locations on Kauai and the leeward side of the Big Island. A wet March resulted in a wet anomaly pattern at the 6- to 8-month time scales and a mixed anomaly pattern could be seen at 9 to 12 months. Molokai to northern portions of the Big Island were dry at the 24-month time scale, a mixed anomaly pattern dominated the state at 36 months, and it was mostly wetter than normal at longer time scales (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 near to above normal across most of the state. Areas of moderate to severe drought were on the islands from Oahu to the Big Island, with extreme drought on Maui and Kaho'Olawe. But the overall drought footprint continued to shrink from 44.7 percent at the end of July to 40.1 percent on the August 31st USDM map.

Alaska

August 2021 was drier than normal across northern Alaska and parts of the Cook Inlet, Northwest Gulf, Bristol Bay and Aleutian regions. At 2 to 5 months, the drier-than-normal conditions persisted in the south central to southwest areas, and were evident in parts of the north, east, and southern panhandle. The northern, eastern, and Cook Inlet areas were dry at the 6- to 12-month time scales. Spotty dryness persisted in these areas, but a mostly wetter-than-normal pattern dominated, 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 anomaly maps for the last 1 and 11 months) (SNOTEL basin precipitation anomaly map for October 2020-August 2021) (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 was mostly cooler than normal, with warmer than normal conditions becoming evident in the east and south at 2 to 3 months. At the 4- to 9-month time scales, it was warmer than normal in the Southwest and near to cooler than normal elsewhere (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, 12 months) (Leaky Bucket model temperature percentile map). Modeled soil moisture and experimental satellite-based observations of soil moisture (SMOS; GRACE root zone and surface soil moisture; and SPoRT percentiles for 0-10 cm [0-4 inches] depth, 0-40 cm [0-16 inches] depth, 0-100 cm [0-39 inches] depth, 0-200 cm [0-79 inches] depth) and groundwater showed drier-than-normal conditions lingering in parts of the northeast, Bristol Bay, and south coastal areas. Satellite observations of vegetative health (stressed vegetation, VHI, drought-related stress) showed evidence of some stressed vegetation in central to east-central areas. Monthly streamflow was mostly near normal with some below-normal streamflows in the Cook Inlet and Northwest Gulf regions. The month began with several large wildfires burning in the central to eastern interior regions, but these ended by the end of the month (wildfire maps for August 1, 4, 9, 13, 17, 24, 26, 31). According to the National Interagency Fire Center's (NIFC) National Interagency Coordination Center, as of August 31st, 254,094 acres have been burned in Alaska so far this year. Enough precipitation fell in the abnormally dry and and moderate drought areas this month to eliminate drought and dryness on the August 31st USDM map.

Puerto Rico and U.S. Virgin Islands

August 2021 was drier than normal across most of Puerto Rico (PR) and the U.S. Virgin Islands (USVI). Drier-than-normal conditions dominated the southern islands (St. Croix) in the USVI at all time scales, and the northern islands were drier than normal except for the 3- to 6-month time scales which were wetter than normal on St. Thomas. PR was mostly drier than normal at the 2- and 4- to 36-month time scales, especially in the southern areas at 3 to 9 months, with a mixed to wetter-than-normal pattern evident at other time scales (radar-based precipitation anomaly estimates for the last 1, 2, 3, 6, 8, 11, 12 months) (low elevation station precipitation 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).

Root zone analyses indicated that soil conditions were dry along the southern and northern coasts and eastern interior regions of PR. Monthly streamflow in PR was below normal in southern and northwestern coastal areas, with a mixed anomaly pattern in the east. Groundwater on the USVI rose earlier in the month, due to rain from Tropical Cyclones Fred and Grace which passed south of the USVI. But groundwater levels declined later in the month and continued well below peak levels of the last couple years (groundwater level graphs for St. Croix, St. Thomas, and St. John). Moderate drought shrank to about 4.1 percent of Puerto Rico. In the USVI, severe drought improved to moderate drought on St. Croix, moderate drought improved to abnormal dryness on St. John, and abnormal dryness ended on St. Thomas.

CONUS State Precipitation Ranks

August 2021 was drier than normal across the Far West and parts of the Southwest, Plains, Midwest, and northern New England. Six states in these regions had a precipitation rank in the driest third of the 127-year historical record for August.

June-August 2021 was drier than normal across the Far West, Pacific Northwest, northern and central Plains, Upper Mississippi Valley, and parts of northern New England, with record dryness occurring locally in parts of northern Minnesota and the High Plains where Colorado, Nebraska, and Kansas conjoin. Thirteen states in these regions had a precipitation rank in the driest third of the historical record for June-August, including two in the top ten driest category — Minnesota (seventh driest) and Montana (tenth driest).

March-August 2021 was drier than normal in the same areas as June-August, plus the central Appalachians to Carolinas and southern Florida, with record dryness occurring locally in parts of the Pacific Northwest. Eleven states in these regions had a precipitation rank in the driest third of the historical record for March-August, including seven in the top ten driest category — Oregon and Washington (both second driest), Idaho (third driest), California and Montana (both fourth driest), Minnesota (eighth driest), and North Dakota (tenth driest).

The year to date (January-August) was drier than normal in the same areas as March-August, with record dryness occurring locally in parts of the Pacific Northwest, northern Plains, and Upper Mississippi Valley. Twelve states in these regions had a precipitation rank in the driest third of the historical record, including four in the top ten driest category — Montana (fifth driest), Minnesota (sixth driest), North Dakota (seventh driest), and California (ninth driest).

The last 12 months (September 2020-August 2021) were drier than normal across most of the West, central to northern Plains, and Upper Mississippi Valley, and parts of the southern High Plains, Great Lakes to Ohio Valley, and Northeast, with record dryness occurring locally in parts of California and Minnesota. Sixteen states in these regions had a precipitation rank in the driest third of the historical record, including seven in the top ten driest category — California (driest on record), Nevada (second driest), Minnesota (fourth driest), North Dakota (fifth driest), South Dakota (sixth driest), Idaho (ninth driest), and Montana (tenth driest). Utah (eleventh driest) and Washington (13th driest) almost made the top ten category.

Agricultural Belts

During August 2021, the Primary Corn and Soybean agricultural belt generally had warmer-than-normal temperatures and was wetter than average in the north and south with a band of below-average precipitation in the middle. The month ranked as the 24th wettest and 19th warmest August, regionwide, in the 1895-2021 record.

March marks the beginning of the growing season for the Primary Corn and Soybean agricultural belt. March-August 2021 was warmer than normal in the north and near normal in the south with precipitation drier than normal in the north and near to wetter than normal in the south. The period ranked as the 30th wettest and 15th warmest March-August, regionwide, on record.

During August 2021, the Spring Wheat agricultural belt was near to warmer than normal and mostly near to wetter than normal. The month ranked as the 28th wettest and 29th warmest August, regionwide, in the 1895-2021 record.

March marks the beginning of the growing season for the Spring Wheat agricultural belt. March-August 2021 was warmer and drier than normal. The period ranked as the fifth driest and fourth warmest March-August, regionwide, on record.

As of August 31, drought affected approximately 99 percent of spring wheat production, 88 percent of barley production, 52 percent of the sheep inventory, 42 percent of the milk cow inventory, 36 percent of hay acreage, 35 percent of winter wheat production, 32 percent of corn production, 30 percent of the cattle inventory, 28 percent of soybean production, 20 percent of rice production, 12 percent of sorghum production, and 4 percent of cotton production.

August 29 USDA reports indicated that topsoil moisture was short or very short (dry or very dry) across 47 percent of the CONUS and subsoil moisture was short or very short across 49 percent of the CONUS. Forty-four percent of the pasture and rangeland was in poor to very poor condition, nationwide, while 14 percent of the corn crop and 15 percent of soybeans were in poor to very poor condition. Those states having 30 percent or more of the topsoil or subsoil moisture short or very short, or 30 percent or more of the pasture and rangeland in poor to very poor condition, at the end of August 2021 are listed in the table below.

August 2021 statewide table of percent of pasture and rangeland in poor or very poor condition and percent of topsoil and subsoil moisture short or very short

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, American Samoa, basinwide), August 2021 was drier-than-normal in parts of the Marianas and Palau, and much of the RMI and FSM. It was near to wetter than normal in other parts of the Marianas and Palau, and in American Samoa.

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 Chuuk, Kapingamarangi, and Pingelap (in the FSM) and Ailinglaplap, Jaluit, Kwajalein, and Wotje (in the RMI). August precipitation was above the monthly minimums in the Marianas, Palau, American Samoa, and the rest of the USAPI stations in the FSM and RMI. 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 2021, which is in the wet season or entering the wet season for most locations in Micronesia. Precipitation was above the monthly minimum but below normal (1981-2010 normal), because the normals are high, at:

  • Kosrae: August 2021 precipitation 9.48 inches, August normal mean 14.81 inches, August normal median 14.22 inches
  • Lukunor: August 2021 precipitation 8.83 inches, August normal mean 14.18 inches, August normal median 14.04 inches
  • Majuro: August 2021 precipitation 10.60 inches, August normal mean 11.42 inches, August normal median 11.69 inches
  • Pohnpei: August 2021 precipitation 9.35 inches, August normal mean 14.82 inches, August normal median 14.26 inches
  • Saipan: August 2021 precipitation 10.95 inches, August normal mean 12.15 inches, August normal median 13.13 inches
  • Yap: August 2021 precipitation 12.84 inches, August normal mean 15.46 inches, August normal median 14.82 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
2020
Oct
2020
Nov
2020
Dec
2020
Jan
2021
Feb
2021
Mar
2021
Apr
2021
May
2021
Jun
2021
Jul
2021
Aug
2021
Sep-
Aug
Chuuk167%92%127%182%114%156%223%55%244%60%135%48%124%
Guam NAS87%146%140%157%102%33%130%119%210%82%86%105%94%
Kapingamarangi9%15%31%38%65%63%78%150%129%72%99%52%64%
Koror62%170%88%142%102%166%119%287%178%56%73%101%108%
Kosrae114%149%177%185%188%141%194%106%154%194%166%67%129%
Kwajalein144%140%115%60%74%75%264%174%126%67%82%35%102%
Lukonor134%105%102%219%146%180%84%134%238%105%41%63%110%
Majuro101%176%112%147%150%57%228%135%285%84%84%91%133%
Pago Pago228%201%160%113%132%141%91%76%80%212%84%145%117%
Pohnpei120%121%169%168%147%65%216%77%152%141%93%66%126%
Saipan74%104%88%193%91%122%46%77%120%158%123%83%99%
Yap81%104%196%200%201%139%189%316%109%86%67%87%122%
Pacific Island Precipitation (Inches)
Station Name Sep
2020
Oct
2020
Nov
2020
Dec
2020
Jan
2021
Feb
2021
Mar
2021
Apr
2021
May
2021
Jun
2021
Jul
2021
Aug
2021
Sep-
Aug
Chuuk19.61"10.57"13.45"20.47"11.56"11.29"18.55"6.86"27.53"7.00"16.13"6.20"169.22"
Guam NAS10.96"16.75"10.33"8.02"4.11"1.01"2.70"3.02"7.14"5.08"8.76"15.44"93.32"
Kapingamarangi0.86"1.19"2.83"3.77"5.92"5.86"8.91"20.44"15.53"9.95"14.01"4.26"93.53"
Koror7.28"20.11"9.97"15.82"10.42"14.23"8.84"21.03"21.06"9.87"13.55"13.66"165.84"
Kosrae16.16"16.25"24.52"29.87"31.36"18.28"31.20"18.63"27.37"28.33"24.77"9.48"276.22"
Kwajalein15.51"15.64"12.95"4.02"2.34"1.97"6.21"9.17"8.45"4.61"8.05"3.43"92.35"
Lukonor13.63"11.83"9.23"24.71"12.29"16.11"7.81"15.21"27.86"12.26"6.61"8.83"166.38"
Majuro11.25"22.35"14.99"16.71"11.58"3.89"15.00"12.71"28.81"9.28"9.42"10.60"166.59"
Pago Pago14.90"18.63"16.25"14.55"17.62"16.86"9.68"7.14"7.71"11.32"4.64"7.82"147.12"
Pohnpei15.02"18.49"25.13"26.95"19.38"6.24"28.50"14.18"30.38"20.95"14.30"9.35"228.87"
Saipan7.46"11.08"4.95"7.43"2.30"3.15"0.86"2.02"2.85"5.71"10.94"10.95"69.7"
Yap10.98"12.71"17.27"16.99"12.85"7.24"8.63"17.78"8.59"10.35"10.13"12.84"146.36"
Pacific Island 1981-2010 Normal Median Precipitation (Inches)
Station Name Sep
2020
Oct
2020
Nov
2020
Dec
2020
Jan
2021
Feb
2021
Mar
2021
Apr
2021
May
2021
Jun
2021
Jul
2021
Aug
2021
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, Kapingamarangi was drier than normal in the short term (August and the last 3 months [June-August 2021]) and long term (year to date [January-August 2021] and last 12 months [ September 2020-August 2021]). Guam and Kwajalein were drier than normal for 3 time periods and near normal for the fourth time period. Chuuk, Lukunor, Majuro, Pohnpei and Yap were drier than normal in the short term and near to wetter than normal in the long term. Airai, Kosrae, and Saipan were near to wetter than normal for 3 time periods and drier than normal for the fourth time period. Pago Pago was near to wetter than normal in both the short term and long term.

Based on percent of normal average (instead of normal median values), in the Marianas Islands, precipitation during August was generally below normal across the islands. A mixed anomaly pattern to mostly drier-than-normal pattern was evident at longer time scales (percent of normal precipitation maps for the last 1, 2, 3, 4, 5, 6, 8, 9, 11, 12, 24, 36, 48, 60 months).

In the Marshall Islands, August was drier than normal across most of the islands. The last 2 to 3 months were predominantly drier than normal. It was drier than normal on most of the islands and wetter than normal in the southeast at the 4- to 8-month time scales, with a mixed anomaly pattern at longer time scales (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 31st USDM produced for the USAPI, moderate drought developed at Ailinglaplap with abnormal dryness in the RMI at Jaluit, Kwajalein, and Wotje, and in the FSM at Chuuk and Kapingamarangi. The National Weather Service noted that water rationing was reported on Ailinglaplap at the end of the month, but the crops were still green and healthy. Storage in the Majuro reservoir fluctuated up and down throughout the month, reaching a maximum of 31.6 million gallons on the 12th and a minimum of 27.8 million gallons on the 3rd, and ending the month at 30.3 million gallons, which is above the 28.8 million gallon threshold for concern.

August 2021 precipitation ranks were low at several stations. Wet conditions during previous months moderated ranks for longer time periods at some, while long-term dryness was still evident at others:

  • Ailinglaplap: August 2021 was the driest August in the 37-year record, as were July-August, June-August, May-August, and April-August. But long-term conditions were wet, with September-August ranking as fourth wettest.
  • Kwajalein: driest August out of 70 years of data, second driest June-August, third driest July-August, and fifth driest May-August.
  • Jaluit: July-August 2021 was second driest out of 38 years of data.
  • Chuuk: third driest August (71-year record) and fifth driest June-August.
  • Lukunor: second driest August (25 years), second driest July-August, and third driest June-August.
  • Kapingamarangi: seventh driest August (31 years), with drier ranks at longer time scales, including third driest September-August.
  • Pohnpei: fifth driest August (71 years) and seventh driest July-August, but fourth wettest September-August.
  • Pingelap: sixth driest August in a 37-year record.

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 2021, March-August 2021 (last 6 months), and September 2020-August 2021 (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 2021 USAPI Precipitation Ranks (1 = driest)
StationAugust 2021Mar-Aug 2021Sep 2020-Aug 2021Period of Record
RankYearsRankYearsRankYears
Ailinglaplap137163732351981-2021
Chuuk371507064701951-2021
Fananu--6--3--32003-2021
Guam3765286528641957-2021
Jaluit1338103710351981-2021
Kapingamarangi73112243191962-2021
Koror3170516955691951-2021
Kosrae1053384331331954-2021
Kwajalein170236922691952-2021
Lukunor425152520241981-2021
Majuro2668586762671954-2021
Mili19373636--331981-2021
Nukuoro1338243725361981-2021
Pago Pago3856215546551966-2021
Pingelap637273628331981-2021
Pohnpei571587067701951-2021
Saipan1941264013321981-2021
Ulithi539--36--331981-2021
Utirik--16--7--41985-2020
Woleai1240273224271968-2021
Wotje2438143723341981-2021
Yap3071457061701951-2021
Map of USAPIAugust 2021 Precipitation (Inches)
Map of USAPI August 2021 Percent of Normal Precipitation
Map of USAPI June 2021-August 2021 Percent of Normal Precipitation
Map of USAPI January-August 2021 Percent of Normal Precipitation
Map of USAPI September 2020-August 2021 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, August temperatures were near average across much of the Southeast region while precipitation varied across the region, with the driest locations found across much of the Florida Peninsula, central North Carolina, central Alabama, and Puerto Rico. Monthly precipitation totals ranged from 70 to less than 25 percent of normal across these locations. Indeed, Lakeland, FL (1948-2021; 2nd driest August) measured only 3.97 inches (101 mm) of precipitation, which was more than 5 inches (127 mm) below average. From the 16th through the 19th, Tropical Storm Fred impacted the region, causing heavy rainfall and strong thunderstorms. The wettest locations for the month were located across most of Virginia, western North Carolina, and northern Georgia.

Drought conditions changed very little across the Southeast region for August. Abnormally dry conditions (D0) were confined to western North Carolina and the western part of Virginia, with a small pocket of moderate drought (D1) in western Virginia. Drought remained the same across Puerto Rico, with an area of moderate drought (D1) in the southern part of the island ringed by an area of abnormally dry conditions (D0). The citrus growing region in Florida experienced a decrease in precipitation for the month forcing farmers to irrigate in several areas.

South

As explained by the Southern Regional Climate Center, August 2021 was the hottest month of the year so far for every state in the Southern region, while rainfall was quite variable across the South. The largest rainmaker was Hurricane Ida, which produced copious amounts of precipitation across eastern Louisiana and southern Mississippi. Oklahoma was the only state drier than median, with an average of 2.53 in (64 mm) that places it 55th driest historically.

Most of the southern United States remained drought-free in August. Isolated areas of abnormal dryness were found in Arkansas and Tennessee, while drought itself (D1 or greater on the USDM) was confined to western Texas and Oklahoma. Severe drought was indicated on August 31 in parts of two counties in northwestern Oklahoma. Excessive rainfall was a much greater problem for Mississippi, Tennessee, and parts of Louisiana, while near-normal precipitation in Arkansas, Oklahoma, and Texas was generally beneficial for farmers, ranchers, and water suppliers.

Midwest

As described by the Midwest Regional Climate Center, August temperatures averaged slightly above normal across most of the Midwest and precipitation amounts varied from 1.50 inches (38 mm) to over 10.00 inches (254 mm). The heaviest rainfall amounts occurred in a swath from southern Minnesota/northwest Iowa through central Wisconsin into east-central Michigan. The lowest precipitation amounts were in northern Minnesota, central Missouri, and central Illinois. These patterns translated to over 200 percent of normal in the wettest locations and 50 to 75 percent of normal in the driest regions. Summer (June, July, and August) precipitation was similar except Michigan was overall wetter than normal and most of Minnesota and Iowa were below normal. Regionwide precipitation was 4.33 inches (110 mm) which was 0.66 inches (17 mm) above normal.

The area of Midwest affected by drought slightly increased in August from 34.7 percent to 38.3 percent. Most of Minnesota, Iowa, and the upper peninsula of Michigan were impacted with isolated areas along the Wisconsin-Illinois border and central Indiana. For the first time in the USDM's history (since 2000), Minnesota had areas in the D4-Exceptional Drought category, which is the worst category of drought. The Greenwood Lake Fire in Minnesota started on August 15th and continued into September, requiring dozens of residents to evacuate.

Northeast

As explained by the Northeast Regional Climate Center, the Northeast experienced its second hottest August on record and received 4.91 inches (124.71 mm) of rain during the month, 122 percent of normal, making it the region's 20th wettest August on record. Nine of the 12 Northeast states were wetter than normal in August, with precipitation ranging from 69 percent of normal in Maine to 150 percent of normal in New Jersey. Summer 2021 was the 10th wettest on record for the Northeast. The region picked up 14.87 inches (377.70 mm) of rain, 116 percent of normal. State precipitation ranged from 84 percent of normal in Maine, the lone drier-than-normal state, to 147 percent of normal in Massachusetts.

The August 3 USDM released on August 5 showed 2 percent of the Northeast in severe drought, 8 percent in moderate drought, and 18 percent as abnormally dry. Drought or abnormal dryness was present in nine of the 12 Northeast states. Severe and moderate drought and abnormal dryness persisted in northeastern New York, northern New England, and Cape Cod, Massachusetts, during the month. In southern parts of the region, including portions of Pennsylvania, Delaware, Maryland, and West Virginia, moderate drought and/or abnormal dryness were introduced/expanded during the first week of August; however, heavy rainfall, particularly from tropical systems Fred and Henri, allowed dryness to ease in parts of those states by month's end. The USDM released on August 26 showed 2 percent of the Northeast in severe drought, 9 percent in moderate drought, and 12 percent as abnormally dry. A few sites in northern New England saw daily record or near-record low streamflow and/or groundwater levels during August. Seventy-five community water systems in New Hampshire had water restrictions in place as of August 18, with 64 of them having mandatory restrictions. Several wells ran dry or experienced water shortages in Maine. As of mid-August, 17 dry wells had been reported in Maine. Due to drought conditions earlier this summer and increased water demand, the Stonington, Maine, municipal water supply, which relies on wells, ran low. The town trucked in water from a nearby town at a cost of around $20,000. According to the Maine Drought Task Force, some trees were experiencing drought stress and "severe drought in northwestern Maine continues to affect the growth of hay and corn."

High Plains

As summarized by the High Plains Regional Climate Center, temperatures varied across the region for the month but remained above normal for most of the region, while dry conditions remained for much of the High Plains, barring several pockets of above-normal precipitation. This precipitation disparity was observed in many states but most prominently in South Dakota. The northeast portion of South Dakota observed precipitation over 5 inches (127 mm) above normal ranking some areas in the top 10 wettest August on record. This contrasted with the southwestern portion of the state which observed precipitation totals between 2 and 3 inches (51-76 mm) below normal. Outside of these isolated areas of above-normal precipitation, most of the region observed precipitation totals below normal for August. Most of Kansas, Colorado, Nebraska, and portions of North Dakota, South Dakota, and Wyoming had below-normal precipitation totals. These below-normal conditions led to a new record in Alamosa, Colorado. Alamosa ranked as the driest August on record with 0.10 inch (2.5 mm) of precipitation for August. This lowered a previous record set in 1944 of 0.11 inch (2.7 mm). Colorado Springs observed its 4th driest August on record with 0.20 inch (5 mm) reaching only 7 percent of its normal precipitation for the month.

Drought conditions persisted across the region, as warm temperatures and minimal precipitation continued for August. This has led to several impacts across our region, most of which were observed in the Northern High Plains. Extreme heat and drought conditions have weakened beehives in North Dakota, a leader in U.S honey production. This has led to dwindling hive sizes and a decrease in the honey production for the year. These effects have the potential to impact other areas in the U.S. Beehives from North Dakota are transported to California in winter months to help with almond tree pollination, and with reduced bee sizes there is the potential for less pollination. Pastures and rangeland across Wyoming, North Dakota, and South Dakota continue to fare poorly. According to the USDA, 85 percent of pastures and rangeland in North Dakota, 83 percent in South Dakota, and 68 percent in Wyoming are in poor to very poor condition. Crops also continue to fare poorly in the region. In South Dakota Spring Wheat ended the crop season with 75 percent in poor to very poor condition. Extreme heat has quickened the process of crop growth this season causing earlier than average maturation and harvest. Temperatures and lack of precipitation aren't the only thing impacting crop conditions: Grasshoppers, which have thrived in the warm, dry conditions, are causing major havoc on crops by eating them to the ground in some areas. This, along with low and poor quality stock ponds, has impacted cattle in the region causing many ranchers to sell their cattle.

West

As described by the Western Regional Climate Center, August 2021 was characterized by an anomalously strong offshore ridge centered in the eastern North Pacific Ocean. The position of the ridge west of North America brought largely seasonable, albeit hot, temperatures to the western U.S. but kept the northwestern regions drier than normal. Despite generally seasonable temperatures at the monthly scale, the Pacific Northwest experienced another heatwave. However, this event was shorter in duration and less severe in magnitude than the record-breaking June 2021 event. The hot and dry conditions allowed wildfire activity to continue throughout the west, with many notable large fires burning throughout Washington, Oregon, Idaho, and California leading to poor regional and local air quality as well as disrupting economies and displacing humans and wildlife.

Temperatures in the West were near-average during August, with slightly above normal (0-2F; 0-1.1C) temperatures in the majority of regions. Owing to increased cloud cover and likely some land surface feedbacks, slightly below average (0-2F; 0-1.1C) temperatures were observed in the regions receiving above-normal rainfall. As is common during summer, precipitation in the West was varied. California, Oregon, and Washington remained extremely dry. The Intermountain West received well-above normal rainfall as an active Southwestern monsoon continued through August, favoring poleward moisture transport.

Sea surface temperatures (SST) in the vicinity the Hawaiian Islands were near to slightly below average (0-1.5F; 0-0.8C) above normal. Temperatures on the Hawaiian Islands in August were generally near-normal. With a mean temperature of 77.7F (25.6C) Hilo, HI (Hawai'i) recorded its thirteenth hottest August (1.1F (0.6C) above normal) since 1950. Drought conditions continued on all islands as August precipitation was below normal despite beneficial rainfall from Hurricane Linda. Maui is experiencing the most severe drought conditions while all parts of Lana'i, Kaho'olawe, and Ni'ihau are in some level of drought according to the USDM.

August brought slightly cooler and much wetter than normal conditions to Alaska. However, northwestern and interior Alaska experienced hot conditions early in the month. The central interior finished August with 200-300% of normal rainfall. This rainfall helped mitigate wildfire activity. The 2021 Alaskan wildfire season ended with approximately 254,000 acres (103,000 ha) burned, which is less than half of the long-term median. Daily sea ice extent in the Chukchi was the highest since 2006. While extensive, other indicators, such as the declining area of multiyear ice in the Arctic, suggest this ice is young and thus thin.

Additional Resources


Citing This Report

NOAA National Centers for Environmental Information, Monthly Drought Report for August 2021, published online September 2021, retrieved on June 23, 2024 from https://www.ncei.noaa.gov/access/monitoring/monthly-report/drought/202108.