JACKSONVILLE, Fla. – In September, as Hurricane Sally slowly churned through the Gulf into Alabama, people in the crossfire had extra time to evacuate from the Category 2 storm between Pensacola and Mobile.
The delay came with a perilous price. Sally’s lumbering pace slowed under 5 mph at times resulting in tremendous flooding.
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Without a quick exit, days of rain resulted in over 20 inches of rainfall between Alabama and the Florida Panhandle.
Research shows incidents like these copious tropical rainfall events are happening more frequently because tropical systems are moving slower.
A 10% slowdown in hurricane speed can more than double rainfall totals caused by a 1.8°F increase of global warming, according to NOAA Hurricane researcher James Kossin.
The record-breaking 30 named storms during 2020 has been marked by a parade of wet storms making landfall on the Gulf Coast, without any reprieve from the preceding years’ hurricane onslaught.
The 2017 and 2018 Atlantic hurricane seasons set records for rainfall totals. Harvey was the wettest hurricane in U.S. history, and yet Hurricane Sally’s rainiest locations over Alabama came within about a foot and a half of matching Hurricane Harvey which submerged Huston with 2 to 4 feet of rain in 2017.
Just last year, Tropical Storm Imelda became the second wettest Texas storm after Harvey and ranked as the third slowest storm to strike the U.S. Recent years echoed similar statewide flooding records with Hurricane Florence dropping 35.93 inches in Elizabethtown, NC.
Scientists say the warming planet is driving the physics behind slower storms, which is also pushing up the intensity of the strong hurricanes.
A warmer atmosphere can hold more moisture and equalizes the differences between pressure patterns resulting in less forceful movements needed to push hurricanes along.
Just before the start of this year’s record major hurricane season, James Kossin released another paper in the Proceedings of the National Academy of Sciences, that showed an increasing trend of stronger winds in hurricanes.
Kossin examined satellite data from 1979 to 2017 and found hurricanes across the globe hurricanes are getting stronger by 6% each decade.
The alarming trend has boosted the potential for higher-end major hurricanes by about 25% compared to what the planet saw on average 40 years ago.
This season had twice as many Category 3 or higher storms compared to an average year underscoring this research.
Category 4 Hurricane Laura was the first of six major hurricanes this season. It was the strongest hurricane to hit the Pelican State since 1856.
In all, an unprecedented six storms all had winds over 111 mph including Category 5 Iota, the latest most powerful hurricane in the Atlantic basin. It along with Hurricane Eta rapidly intensified becoming the first time for two major hurricanes in November.