Hurricanes and Tropical Storms - Annual 2017
2017 Season Summary:
The 2017 North Atlantic hurricane season had 17 named storms, 10 hurricanes, and six major hurricanes. This is well above the 1981-2010 average of 12.1 named storms, 6.4 hurricanes, and 2.7 major hurricanes. The number of named storms ranked as the ninth most on record, the number of hurricanes ranked as the eighth most, and the number of major hurricanes ranked as the third most. The lack of El Nino conditions in the equatorial Pacific, with La Nina conditions developing near the end of the season, likely helped to boost the seasonal numbers. When ENSO neutral and La Nina conditions are present, wind shear in the Atlantic Basin is typically less, creating favorable conditions for tropical cyclone development. Three of the major hurricanes — Harvey, Irma, and Maria — impacted the U.S. mainland and territories causing approximately $265 Billion in damages, contributing to the costliest year in terms of weather and climate disasters for the nation. September was an extremely active hurricane month for the North Atlantic Basin with five hurricanes — four of which were major hurricanes active in the basin. One measure of tropical cyclone activity, the Accumulated Cyclone Energy (ACE) index, which takes into account the combined strength and duration of tropical cyclones — was record high in the North Atlantic during September.
During the 2017 North Atlantic hurricane season, three tropical storms and four hurricanes, made landfall in the U.S. (including Puerto Rico). This is the most hurricane landfalls since 2005 in the U.S. and the landfall of Hurricane Harvey marked the end of a record-long streak of over 4,300 days with no major Hurricanes making landfall in the United States. Prior to Harvey, the last major hurricane to make landfall in the U.S. was Hurricane Wilma in November 2005.
Harvey was also noteworthy for the amount of precipitation it dropped on parts of coastal Texas and Louisiana with reports of over 60 inches of rainfall over five days inundating parts of the Houston metro area. Damages from Harvey exceeded $125 billion, only exceeded by Hurricane Katrina. Hurricane Irma reached maximum strength with maximum sustained winds of 185 mph, tying as the second most intense hurricane on record for the basin. Irma maintained that strength for at least 37 hours, marking the longest that a tropical cyclone has remained that strong anywhere on the globe. Irma made landfall in the Florida Keys at a Category 4 storm, marking the first time that two Category 4 hurricanes have made landfall in the contiguous U.S. in the same year. Irma caused $50 billion in damages. Hurricane Maria made landfall in southeastern Puerto Rico has a Category 4 hurricane, the strongest tropical cyclone to impact the island since 1928. Maria's high winds caused widespread devastation to Puerto Rico's transportation, agriculture, communication and energy infrastructure. Damages from Maria are estimated at $90 billion.
The Accumulated Cyclone Energy (ACE) index of tropical cyclone activity also indicated an above-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 2017 Atlantic hurricane season had an approximate ACE of about 226 (x104 knots2) which was more than double the 1981-2010 average value of 104 (x104 knots2) and ranked as the seventh highest value since reliable records began in the 1800s. Almost half of the ACE during the 2017 was attributable to just two hurricanes — Irma and Maria due to their intensity and longevity.
East Pacific Basin
2017 Season Summary:
The 2017 East Pacific hurricane season had 18 named storms, including nine hurricanes, four 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. Five Eastern Pacific tropical cyclones made landfall in 2017. Tropical Storm Selma made landfall in El Salvador and tropical storms Beatrix, Calvin, Lidia and Hurricane Max made landfall in Mexico. Tropical Storm Selma was the first named tropical cyclone on record to make landfall in El Salvador. Tropical Storm Adrian formed on May 9th, marking the earliest occurrence of a named storm in the East Pacific basin. The previous earliest occurrence was Tropical Storm Alma forming on May 12, 1990. For the first year since 2012 no tropical cyclones passed near the Hawaiian Islands. The ACE index for the East Pacific basin during 2016 was 98 (x104 knots2), which is below the 1981-2010 average of 132 (x104 knots2 ) and the lowest since 2013.