2015 Season Summary:
The 2015 North Atlantic hurricane season had eleven tropical storms, four hurricanes, and two major hurricanes. The number of tropical storms was below the 1981-2010 average of 12.1; the number of hurricanes was below the 1981-2010 average of 6.4; and the number of major hurricanes was near the 1981-2010 average of 2.7. The number of tropical cyclones was more than the eight that occurred during the 2014 season. When El Niño conditions are present in the equatorial Pacific like in 2015, tropical cyclone activity across the North Atlantic basin tends to be suppressed due to increased wind shear, an unfavorable condition for tropical cyclone development.
Two tropical storms, Ana and Bill, made landfall in the contiguous U.S. during the season. The largest impacts of both of these systems were heavy rain across the Carolinas when Ana made landfall in May and heavy rain across the Southern Plains and Midwest when Bill made landfall in June. No hurricanes or major hurricanes made landfall. The 2015 hurricane season marks a continuation of a record-long streak of no major hurricanes (Category 3 or stronger) making landfall in the United States. The last major hurricane to make landfall in the U.S. was Wilma on November 24, 2005. This major hurricane drought surpassed the length of the eight-years from 1861-1868 when no major hurricane struck the United States' coast. On average, a major hurricane makes landfall in the U.S. about once every three years. Even through Major Hurricane Joaquin did not make direct landfall in the U.S., moisture associated with the system interacted with an upper level trough across the Southeast bringing record rainfall and flooding to parts of the Carolinas.
The Accumulated Cyclone Energy (ACE) index of tropical cyclone activity also indicated a below-average season in the North Atlantic. The ACE index is used to calculate the intensity of the hurricane season and is a function of the wind speed and duration of each tropical cyclone. The 2015 Atlantic hurricane season had an approximate ACE of about 60 (x104 knots2) which was below the 1981-2010 average value of 104 (x104 knots2) and slightly less than the ACE value of 2014. Almost half of the ACE during the 2015 was attributable to a single hurricane, Joaquin, which was the strongest hurricane of the season with maximum sustained winds of 155 mph (Category 4 strength) and a central minimum pressure of 931 mb.
East Pacific Basin
2015 Season Summary:
The 2015 East Pacific hurricane season had 18 named storms, including 13 hurricanes, nine of which became major. The 1981-2010 average number of named storms in the East Pacific is 16.5, with 8.9 hurricanes, and 4.3 major hurricanes. This is the first year since reliable record keeping began in 1971 that the eastern Pacific saw nine major hurricanes. The Central Pacific also saw an above-average tropical cyclone season, with 14 named storms, eight hurricanes, and five major hurricanes, the most active season since reliable record-keeping began in 1971. Three major hurricanes (Ignacio, Kilo and Jimena) were active across the two adjacent basins at the same time, the first time this occurrence has been observed. The ACE index for the East Pacific basin during 2015 was 158 (x104 knots2), which is above the 1981-2010 average of 132 (x104 knots2) and the highest since 2006. The Central Pacific basin ACE during 2015 was 124 (x104 knots2).
Two major hurricane records were broken in the East Pacific basin during 2015. Hurricane Patricia was the strongest hurricane on record in the Western Hemisphere with maximum sustained winds of 200 mph and a central pressure of 879mb. Hurricane Sandra, which formed at the very end of the season in November had maximum sustained winds of 145 mph and was the strongest hurricane in the East Pacific so late in the year. The remnants of several East Pacific tropical cyclones made their way into the contiguous U.S. during the year, bringing flooding rains to parts of Southern California, the Southwest, and the Southern Plains.