January 9th, 2018

2017 North Atlantic Hurricane Season

Posted at 1:00 AM ET

james-wallerJames Waller, PhD, Research Meteorologist

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The 2017 North Atlantic Hurricane season was one of the most active seasons on record, a historic season in many respects, and certainly an impactful one. Those most severely affected residents are facing a long and difficult recovery that could last for years. They continue to have our thoughts and concerns.

In Q1 2018, the National Hurricane Center (NHC) is scheduled to publish a detailed tropical cyclone report for each storm of the 2017 season, following review and quality control of all available data; these reports will inform the official record for the 2017 hurricane season for the North Atlantic Basin. Specifics of each hurricane have been documented elsewhere, but key statistics of note follow below.

  • The 2017 North Atlantic Hurricane season produced 10 hurricanes, six of which were major hurricanes, well above both the long-term and near-term averages.
  • The season produced two category 5 and two category 4 hurricanes.
  • The 2017 season was the 7th most active in recorded history for the Basin. The season produced 226 Accumulated Cyclone Energy (ACE) units, the most since 2005, and surpassed only by the 2004, 2005, 1995, 1933, 1926 and 1893 seasons. For background, ACE is a rough measure of storm duration and lifetime with a definition to be found here. Those seasons prior to the satellite era may have had higher values of ACE than measurable at the time.
  • September 2017 was the most active month in known history for the North Atlantic Basin (for both major hurricane days, and ACE). September 8 produced more ACE than any other Atlantic calendar day in known history.
  • Two category 4 hurricanes made landfall on the continental U.S. for the first time in known history (Harvey and Irma).
  • Hurricane Harvey (August 17-September 1) made landfall on the Texas coast as a category 4 hurricane, following a period of rapid intensification on approach to the coast. Harvey was the first category 4 hurricane to hit Texas since 1961, and the first major hurricane to make U.S. landfall since Hurricane Wilma (2005). Harvey’s slow forward speed and intense rainfall produced excessive rainfall and flood impacts in southeast Texas and southwest Louisiana. A rainfall amount of 60+ inches was reported near Beaumont, Texas, surpassing prior rainfall records for any U.S. tropical cyclone.
  • Hurricane Irma (August 30-September 12) rendered severe impacts to areas of the Leeward Islands and Caribbean as well as Northern Cuba before crossing the Florida Keys as a category 4 hurricane, and making final landfall on southwest Florida as a category 3 hurricane. The storm expanded in size on approach to Florida allowing it to render wind impacts over a very large area of the Southeast, while also driving storm surge impacts well away from the center of circulation including the Florida First Coast area. Irma was the first category 4 hurricane to make Florida landfall since Charley (2004). Irma reached maximum sustained winds of 185 mph, one of only four storms in known Atlantic Basin history to reach sustained winds of 185 mph or more. Irma maintained sustained winds of 185 mph for 37 hours, the longest known duration of such winds for any tropical cyclone on a global basis.
  • Hurricane Maria (September 16-30) rendered especially severe impacts to property and infrastructure in Puerto Rico, the Virgin Islands and areas of the Caribbean following a period of rapid intensification to category 5 status on approach to Domenica. Maria was the most severe hurricane to affect Puerto Rico since 1928.
  • Hurricane Nate (October 4-9) made landfall on the Northern Gulf Coast as a category 1 hurricane, following a period of rapid intensification on approach to the coast. Nate’s fast forward speed of 28 mph impeded intensification to a major hurricane. Nevertheless the storm rendered wind impacts over widespread areas of the Northern Gulf states, as well as storm surge impacts to coastal areas of Alabama and Mississippi. Nate had the fastest 12-hour forward speed of any hurricane on record in the Gulf of Mexico.
  • Hurricane Ophelia (October 9-15) reached major hurricane status in the eastern North Atlantic, the furthest east in known history for the Basin. Ophelia underwent extratropical transition to produce a powerful frontal system that then affected Ireland.
  • Hurricanes Franklin (August 7-10) and Katia (September 5-9) also made landfall on the central Gulf coast of Mexico.
  • Key meteorological factors in play for the 2017 season included very warm sea-surface temperatures, abnormally reduced wind shear, and increased moisture for key areas. This enabled hurricane development and in some cases rapid intensification. Furthermore, the Atlantic subtropical ridge extended further west than was previously observed for most of the 2006-2016 period. The westward extent of the ridge in 2017 tended to suppress storm recurvature until storms had drifted further west, such as occurred with Irma and Maria.

The statements above follow NHC operational advisories, media reports and a seasonal summary produced by Dr. Phil Klotzbach of Colorado State University (CSU).

2017 North Atlantic Hurricane Season

Named Storms (NS)

Hurricanes (HU)

Major (CAT3+) Hurricanes (MH)

Actual

NOAA

CSU

1957-2016 Average

1995-2016 Average

NS

17

14-19

16

11.3

14.6

HU

10

5-9

8

6.1

7.4

MH

6

2-5

3

2.5

3.4

SOURCE: NOAA/NHC, CSU, Guy Carpenter

Top-10 Accumulated Cyclone Energy (ACE) Seasons – North Atlantic Basin

Season

ACE

1933

259

2005

245

1893

231

1926

230

2004

227

1995

227

2017

226

1953

211

1950

211

1961

205

SOURCE: CSU

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Official weather watches and warnings, and statements from official meteorological and emergency management agencies supersede this update, and should be closely followed concerning matters of personal safety.

Guy Carpenter & Company, LLC provides this report for general information only. The information contained herein is based on sources we believe reliable, but we do not guarantee its accuracy, and it should be understood to be general insurance/reinsurance information only. Guy Carpenter & Company, LLC makes no representations or warranties, express or implied. The information is not intended to be taken as advice with respect to any individual situation and cannot be relied upon as such. Please consult your insurance/reinsurance advisors with respect to individual coverage issues. Readers are cautioned not to place undue reliance on any historical, current or forward-looking statements. Guy Carpenter & Company, LLC undertakes no obligation to update or revise publicly any historical, current or forward-looking statements, whether as a result of new information, research, future events or otherwise.

This document or any portion of the information it contains may not be copied or reproduced in any form without the permission of Guy Carpenter & Company, LLC, except that clients of Guy Carpenter & Company, LLC need not obtain such permission when using this report for their internal purposes.

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