Mark Schleifstein / NOLA.com 6 August 2020

Federal climate scientists have upped their forecast for the 2020 hurricane season to “extremely active,” and predict there will be as many as 25 named storms by the end of November.

It’s only the third time that forecasters from the National Oceanic and Atmospheric Administration have tagged a season as extremely active, said Gerry Bell, lead seasonal hurricane forecaster for NOAA’s Climate Prediction Center.

The likelihood of an above-normal hurricane season in the Atlantic has increased to 85%, and there’s now only a 10% chance of a near-normal season and 5% chance of a below-normal season, said Louis Uccellini, director of the National Weather Service, in a telephone news conference Thursday.

The increased potential for hurricanes makes preparing for a tropical storm to hit coastal areas even more important, he said.

“Now is the time to organize family plans and to make the necessary family preparations,” Uccellini said. He urged the public to view more preparedness information at https://www.ready.gov/hurricanes.

The most active season on record was 2005, the year of Hurricanes Katrina and Rita, when there were 31 tropical systems, including 28 named storms. Bell said that conditions for hurricane formation are not as favorable this year as they were then.

NOAA’s updated forecast calls for 19 to 25 named storms with winds of 39 mph or greater, including seven to 11 that will be hurricanes with winds of 74 mph or greater, and with 3 to 6 of those becoming major hurricanes, Category 3 or greater. The hurricane season runs from June 1 to Nov. 30.

Bell cited two major reasons for the increased activity this year:

  • The Atlantic Multi-Decadal Oscillation, a longtime weather pattern that began in 1995 and causes weaker wind shear in the Atlantic, weaker trade winds in the area where hurricanes form in the Atlantic, and winds that are more favorable for storm creation coming off the African coast.
  • An expectation that La Nina cooler water conditions will return to the eastern Pacific Ocean during the next few months, which will also reduce wind shear in the Atlantic over areas where storms form.

He said labeling the season as extremely active resulted from a review of climate model results that that indicated the season’s “accumulated cyclone energy index” – a  measure of  the combination of all the storms’ intensity and duration –  totaled more than 165% of the average for hurricane seasons between 1981 and 2010.

An average hurricane season has 12 named storms, including six hurricanes and three major hurricanes.

This year’s season has already set records with nine named storms and two hurricanes this early in the season. Typically, only two named storms form by early August, and the ninth doesn’t occur until Oct. 4.

Bell said it’s too early to say whether climate change – global warming – is a factor in producing storms this year.

But he said global warming is definitely a factor in the potential effects of tropical storms and hurricanes that will approach land. Warmer ocean water temperatures will cause higher water elevations and greater inundation during high tides occurring along coastlines during storms. Also, that same high-water effect will cause storm surges created by tropical storms or hurricanes to be higher.

Bell said research also has indicated that global warming has the potential of adding several inches of rainfall to storms as they make landfall, as occurred in Houston during Hurricane Harvey in 2017.

Bell said that improved global weather observations, the result of improvements in satellite coverage, has resulted in the identification of two or three more storms named in the earlier part of hurricane seasons since 2000.

NOAA’s forecast update tracks closely with a forecast update announced Wednesday by Colorado State University climatologist Phil Klotzbach, who increased his estimate of named storms to 24 from 16.

In May, NOAA forecasters predicted there would be between 13 and 19 named storms, including six to 10 hurricanes, with three to six being major.

This will be the fifth straight year with above normal numbers of tropical systems, which surpassed the previous record of four years in a row between 1998 and 2001.

During the 2005 season, there were 31 tropical or subtropical systems, including 27 storms that received names during the season, and a 28th that was determined after the season ended to have reached tropical storm strength, but did not get a name.

That year, there were more named storms than the names provided annually by the World Meteorological Organization. The National Hurricane Center used six Greek letter names.

A record also was set in 2005 for the number of hurricanes, 15, including a record seven of those reaching major hurricane status.

“In 2005, Atlantic ocean temperatures were even warmer than this year, and wind conditions were even more favorable,” Bell said. “By this time in 2005, we already had two major hurricanes.”

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