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RMS has released its 2017 North Atlantic Hurricane Season Review documenting one of the most active, damaging, and costliest seasons on record. The 2017 season saw a total of 17 named storms, with ten of these storms reaching hurricane strength and occurring consecutively within a hyperactive period between August and October. The season will be remembered for its six major hurricanes and specifically for the impacts of three of these storms: Harvey, Irma, and Maria.

Season Review
Figure 1: Comparison of the 2017 North Atlantic hurricane season storms to the 1950-2016 and 1996-2016 averages. (Data from the National Oceanic and Atmospheric Administration Hurricane Research Division, 2018)

In total, the contiguous U.S. suffered three hurricane landfalls (Harvey, Irma, and Nate), with 2017 marking the first time on record that two Category 4 or greater hurricanes made landfall over the mainland U.S. in a single season.

Harvey was the first major hurricane (Category 3 or greater on the Saffir-Simpson Hurricane Wind Scale) to make landfall in the U.S. since Wilma in 2005, ending the contiguous U.S. major hurricane landfall drought at 4,323 days. The second, Irma, made landfall over the Florida Keys as a Category 4 hurricane, the first in the state since 2004.

The 2017 North Atlantic Hurricane Season Review highlights:

  • The meteorological characteristics that led to Harvey stalling over Texas; the resulting record-breaking rainfall totals in southeast Texas, and the widespread, unprecedented catastrophic inland flooding in the Houston Metropolitan area.
  • The route of Irma through the Caribbean as a Category 5 major hurricane and the extensive devastation on many of the Caribbean islands and in southeast Florida.
  • The catastrophic damage from Maria in parts of the Caribbean, including Dominica, the U.S. Virgin Islands, and most notably in Puerto Rico, where it made landfall as a Category 4 major hurricane.

Outside of the U.S., the report details the landfalls of Franklin and Katia in Mexico, the impact of a record-breaking three major hurricanes in the northeast Windward Islands, and explores how Ophelia became the easternmost major hurricane in the Atlantic Basin on record.

Season Review
Figure 2: 2017 North Atlantic storm tracks and intensities. (Data from the National Hurricane Center, 2018)

Why Was The 2017 Season So Active?

The 2017 season surpassed most, if not all, preseason forecasts and expectations, especially for estimates of major hurricanes and accumulated cyclone energy (ACE). The question must be asked, then: why was the 2017 North Atlantic hurricane season so active?

The season was characterized by phases of oceanic and atmospheric influences that promoted above-average hurricane activity in the Atlantic. The 2017 North Atlantic Hurricane Season Review explores, in detail, several factors that promoted this hyperactivity, including:

  • The sudden transition of the El Niño-Southern Oscillation (ENSO) to a La Niña phase
  • Above-average sea surface temperatures and high ocean heat content in the tropical Atlantic
  • Large-scale synoptic patterns that created a predominant steering flow towards land, turning an active season into a damaging season

What Might 2018 Bring?

Looking ahead to the 2018 hurricane season, early forecasts by Tropical Storm Risk (TSR) suggests the 2018 season might be slightly above-average, but not at the levels attained during 2017.

The skill of seasonal North Atlantic hurricane forecasts is relatively low in the months prior to the start of the season, but by the start of the official season in June, forecast skill typically increases as the uncertainty of the atmospheric and oceanic variables decreases.

As the final section of the review discusses, the scientific community will monitor the state of North Atlantic sea surface temperatures and the phase of the El Nino-Southern Oscillation (ENSO) as key indicators of 2018 hurricane activity. Check back to the RMS blog in early June for a roundup of the pre-season forecasts accompanying the release of RMS 2018 North Atlantic Hurricane Season Outlook report.

The RMS 2017 North Atlantic Hurricane Season Review is now available on RMS Owl and on rms.com.

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James Cosgrove
James Cosgrove
Assistant Director, Event Response

Based in London, James is an Assistant Director within Moody's RMS Event Response team, supporting real-time event response operations and assisting on various event response projects. James holds a bachelor’s degree in Physical Geography and Geology from the University of Southampton and a master’s degree in Applied Meteorology from the University of Reading.

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