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Jun 01, 2023

Record heat could plant hurricane time bomb in Gulf

The heat dome responsible for record-breaking temperatures and drought in south Louisiana may have also created a ticking time bomb of "ridiculously warm" waters in the northern Gulf of Mexico, which

The heat dome responsible for record-breaking temperatures and drought in south Louisiana may have also created a ticking time bomb of "ridiculously warm" waters in the northern Gulf of Mexico, which could rapidly intensify any tropical storm approaching the state’s coastline, scientists say.

As the peak of hurricane season approaches — generally considered to be around Sept. 10 — conditions in the Gulf will be a major focus of concern for storm trackers.

"All of the shallow waters, including the coastal waters and tidal lakes, are ridiculously warm right now. So it’s primed for anything that works its way in," said Ben Schott, director of the National Weather Service office covering the New Orleans and Baton Rouge areas.

Schott said the average sea surface temperatures off the Louisiana coast are between 89 and 92 degrees — "way above normal than where they usually would have been 10, 20 or 30 years ago." That heat can fuel any approaching storm, especially if it is not limited by drier air or wind shear, Schott said.

This map, in degrees Celsiuis, shows much of the northern Gulf Coast waters are between 31.4 and 32.5 degrees, or 88.5 to 90 or above degrees Fahrenheit. Hurricanes need water temperatures above 78 degrees to survive. (NOAA)

Adding to the warm water threat is the location of the “loop current,” an extension of the Gulf Stream. This year it extends from the Yucatan Straits into the eastern Gulf of Mexico, with a dog-leg west to just off the mouth of the Mississippi River, said Matthieu Le Hénaff, a researcher studying ocean currents with the University of Miami and NOAA.

A tropical storm crossing over the loop current often goes through what forecasters call “rapid intensification,” jumping to as high as Category 5 strength in as little as 72 hours. That’s because the loop contains warm Gulf Stream water extending to 3,000 feet below the surface.

This map shows the location of the "Loop Current," a part of the Gulf Stream that meanders into the Gulf of Mexico and often breaks off, floating around for several months. The current's water is as warm as 79 degrees 1,000 feet below the surface, and acts as fuel for hurricanes. (NOAA)

When a tropical system moves over a warm ocean surface, its intensity draws cooler waters to the surface. If it’s moving slow enough, that can cause the storm to lose strength. The deep, warm water of the loop, however, continues to strengthen storms.

“That bending is comparable to the shape of the loop current during Katrina, actually, but it’s a little further north,” Le Hénaff said. “So that means the loop current system is closer to Louisiana and the Mississippi Delta than it was in 2005.”

Katrina intensified to Category 5 strength while crossing the loop, with winds clocking in at 172 mph at 1 p.m. on Aug. 28, 2005. But when the storm exited the loop, it dropped back to Category 3 strength. Katrina made landfall at Buras at 6:10 a.m. on Aug. 29 with top winds of 125 mph.

Forecast path for Idalia on Monday morning. (National Hurricane Center)

Now, National Hurricane Center forecasters are pointing to the extremely warm water in the expected path of Tropical Storm Idalia — 88 degrees or warmer — as the reason they expect it to rapidly intensify into a Category 3 hurricane by early Wednesday. That's when it is expected to make landfall somewhere along Florida's northwestern coastline, accompanied by storm surge that could reach heights of up to 11 feet.

Schott said this year’s intense heat may have even resulted in deeper warmer water away from the loop current. It has certainly led unusually warm waters north of the traditional shoreline, which will limit the weakening of storms that make landfall.

The extended high pressure that parked over Louisiana this summer, increasing the warm water risk within the Gulf, has also provided a buffer against storms, Schott said.

“If there is any silver lining to a record heat/drought, it is the fact that it’s been our protector for the early portion of the hurricane season,” he said.

Only two early season storms popped up in the Gulf this year before Idalia. Tropical Storm Arlene formed on June 1 off Pensacola, Florida, and actually moved southeast away from the United States, before dissipating two days later.

On Aug. 22, Tropical Storm Harold made landfall at Texas' Padre Island with top winds of 50 mph. The storm weakened into a remnant low the next day.

But it’s too early to say whether the high-pressure dome alone is the reason the 2023 Atlantic hurricane season has not resulted in more Gulf activity, said Jamie Rhome, deputy director of the National Hurricane Center.

“Mother Nature is much more complicated than a simple explanation, a simple cause-and-effect, and one just needs time to do a thorough analysis to figure that out,” Rhome said.

NOAA and Colorado State University seasonal climatologists have predicted an above-average number of storms through the end of the season on Nov. 30.

They point to record warm sea surface temperatures in portions of the Atlantic where hurricanes form as overwhelming the potential effects of wind shear limiting storm creation and growth. The wind shear is supposed to be created by a strong El Nino warm water pattern in the eastern Pacific Ocean this year.

Rhome reminded Louisiana residents to be watchful of tropical weather.

“Any storm in the Gulf is always a challenge because the communities along the Gulf are so vulnerable to coastal flooding,” Rhome said. “And many of them are still recovering from past hurricanes, including communities in Louisiana.”

his work is supported with a grant funded by the Walton Family Foundation and administered by the Society of Environmental Journalists.

Email Mark Schleifstein at [email protected] or follow him on Twitter, @MSchleifstein.