Isaias: Gulf Coast faces hurricane threat as Tropical Depression 9 expected to strengthen

A strengthening tropical depression is poised to become Hurricane Isaias and hit parts of the southern United States this week with heavy rain and strong winds.

Tropical Depression Nine experienced winds of 35 mph and was located about 600 miles south of the mouth of the Mississippi River Tuesday evening.

The system is expected to move east over the Yucatan Peninsula, then turn sharply north toward the northern Gulf Coast. It is expected to strengthen rapidly and become a Category 2 hurricane with winds gusting to 100 mph by Friday.

Isaias will likely bring torrential rain, powerful winds and storm surge to areas from southern Louisiana to the Florida Panhandle beginning Friday. The storm could also spawn several tornadoes as its rainbands whip the coast.

It will be the first hurricane of the year in the Atlantic basin, ending a record expectation linked to the effects of an El Niño likely of record intensity.

Exactly where the storm might be headed or how strong it will be as it nears land isn’t yet set in stone, but anyone along the Gulf Coast, from Louisiana to Florida’s Big Bend, should keep a close eye on the forecast.

Florida Gov. Ron DeSantis declared a state of emergency in 25 counties Tuesday ahead of the storm, urging residents to prepare disaster plans and stockpile hurricane supply kits. State emergency crews are installing generators, fuel, food, water and flood barriers in the Tallahassee and Santa Rosa areas to support the response.

Oil companies are also taking precautions in the Gulf. Shell is evacuating non-essential personnel from six offshore platforms, while BP is removing non-essential workers and securing its offshore facilities, the companies announced Tuesday.

This storm is passing through El Niño-influenced atmospheric conditions that have largely thwarted tropical systems throughout the Atlantic hurricane season thus far. Gulf waters are record-breaking for this time of year, providing plenty of fuel, but that’s only part of the equation.

The bane of Atlantic tropical systems this season has been wind shear. This refers to winds blowing at different speeds and coming from different directions at several levels of the atmosphere. Wind shear can tear apart tropical storms and hurricanes.

This new system benefits from low wind shear in the southern Gulf, but it will find higher wind shear guarding the Gulf Coast to the north, threatening to shred the storm as it approaches.

But the system is also expected to move quickly, so its exposure to higher wind shear may be limited. If the storm were to move more slowly, it could weaken quickly as it meanders through hostile conditions.

The strength and track of the storm are also linked. A stronger storm’s circulation extends higher into the atmosphere, allowing winds at those heights to direct it differently than a weaker system. This trajectory, in turn, will determine the time it spends over warm waters and the intensity of hostile wind shear it encounters, which will determine its strength when it reaches the coast.

Whatever its ultimate fate, heavy rains are a concern across the Gulf Coast and other parts of the South late this week. The storm could bring 3 to 6 inches of rain, with localized precipitation of up to 10 inches in places from southern Louisiana to the Florida Panhandle and Big Bend. Showers could begin to intensify along the coast as early as Friday, then continue to flood the region while seeping further inland throughout the weekend.

As this year has already shown, a hurricane-force system need not have significant consequences, especially in a world that is warming and making tropical systems wetter.

Tropical Storms Arthur and Edward did not last long, but their heavy rains led to significant flash flooding and water rescues. Parts of Louisiana and Mississippi were hardest hit by Arthur’s flooding, while Edward dropped more than 20 inches of rain in East Texas.

Determining the location and severity of flooding, high winds and tornadoes along the northern Gulf Coast is even more difficult because we need to know how strong the storm will be and where exactly it will be heading. These impacts could arrive no earlier than Friday or late Saturday.

What is typical in October and November

Four named storms – tropical force or greater – typically form in October and November, but some hurricane seasons can have a stronger end while others calm down.

The last few years illustrate this ebb and flow from one year to the next. Seven storms formed in October and November 2024, but only two formed during the same period in 2023.

Late-season storms tend to form closer to the United States, including in the Gulf, Caribbean and off the Southeast coast, making them more likely to impact land.

Although storms are generally less numerous, they can still be destructive.

Last year, Category 5 Hurricane Melissa devastated Jamaica during the last week of October.

Hurricane Michael slammed into the Florida Panhandle on October 10, 2018, becoming the last Category 5 hurricane on record in the United States. And Hurricane Sandy is perhaps the most notorious of all: it transformed into a hybrid superstorm in late October 2012 and hit the East Coast.

Super El Niño’s hold on the Atlantic basin means a repeat of the famous late-season hurricanes is less likely this year. Its damaging winds are the main reason this season could be hurricane-free for the first time according to reliable records.