Atlantic, Gulf warming raises risk for tropical development and strong hurricanes
With the buildup of heat across the Atlantic, Gulf, and Caribbean, conditions may soon favor more frequent and intense tropical system, especially as wind shear and dry air begin to ease.
In today’s Forecast Feed, AccuWeather’s Bernie Rayno takes a look at the latest in the tropics.
It has been at least 15 days since the last tropical storm churned waters in the Atlantic. Since then, water temperatures over much of the basin have continued to rise, reaching record-high levels in some areas, increasing the potential for rapid tropical development.
Depressions, storms and hurricane systems play a role in the Earth's massive atmospheric engine by dispersing heat away from the tropics to the mid-latitudes. The more heat builds in the tropics, the greater the potential of multiple strong hurricanes, given that conditions are favorable for them to form in the first place.
"We look not only at sea surface temperatures, but also well down below the surface to reveal the true ocean heat content," AccuWeather Lead Hurricane Expert Alex DaSilva said.
Water temperatures in portions of the Gulf, Caribbean and southwestern Atlantic are near 90 degrees Fahrenheit, well above the threshold of 80 degrees, which is typically the lowest temperature water can be to generate a tropical storm. Waters northwest of Africa, which have been chilly much of the season, have warmed considerably. The ocean heat content in the Gulf is at record high levels.
"The exceptional warmth in the Gulf is troubling."
When the water is warm down deep, it is more likely for a tropical storm or hurricane to intensify rapidly and less likely for an established tropical storm or hurricane to weaken.
“Rapid intensification in the Gulf allows less time to prepare compared to storms strengthening in the central Atlantic,” DaSilva said.
Despite the warming Atlantic, Caribbean and Gulf, a vast zone of dry air and extensive areas with combative winds, known as wind shear, have hindered tropical development over the past couple of weeks.
Much of the dry air has originated from the Sahara Desert and Canada, while the circulation around the central Atlantic high, as well as a large high pressure zone in the eastern United States, has contributed to the strong wind shear.
There is a medium risk in the central Atlantic this weekend, and a low risk in the same area later next week.
"Atmospheric conditions that are much more conducive to tropical development are expected to return next week, and there's all that very warm water sitting there,” DaSilva said.
One area of particular concern for the second half of September extends from the western part of the Caribbean to the Gulf.
"This is a zone that we typically look for tropical activity early in the season and late in the season, but there can be development in this area at any time," DaSilva said.
This hurricane season is now pacing a bit behind the historical average. Six named storms have formed in the Atlantic basin, and only Erin strengthened into a hurricane. By this point in the year, there are typically eight named storms and three hurricanes.
"It is remarkable that our first and only hurricane so far this season exploded from a tropical storm into a Category 5 in less than 25 hours," DaSilva said.
It illustrates how favorable atmospheric conditions and warm water can contribute to rapid storm intensification.
"Tropical activity is expected to increase in the coming weeks as conditions gradually become more favorable for development," DaSilva stated. "More tropical activity will increase the risk for direct impacts to the Caribbean and U.S. coastlines."
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