PENSACOLA, United States (AFP) — Hurricane Isaias’s outer bands began lashing the US Gulf Coast on Friday, with the category three storm triggering mandatory evacuations and poised to bring life-threatening storm surge when it makes landfall by evening.

Isaias is the first hurricane of an Atlantic season held in check by a historic El Nino phenomenon, and is set to become the first hurricane to strike the US mainland since Milton in 2024.

Fueled by record-warm Gulf waters heated by climate change, it strengthened rapidly over the past day.

“Isaias is coming in right over us,” Jane Drescoll, a 63-year-old resident of Pensacola, told AFP, holding on to her hat as she spoke to AFP on the beach. She said she had stocked up on propane and water and had been through eight hurricanes since moving to the area a decade ago.

The storm’s intensity could fluctuate through the afternoon, but forecasters expect it to slam into the western Florida panhandle at or near major hurricane strength — meaning category three — before weakening over land. Tropical storm conditions began along the northern Gulf Coast as of Friday afternoon.

The National Hurricane Center (NHC) said Isaias was packing maximum sustained winds of 120 miles (195 kilometres) per hour, and was located about 145 miles south of Pensacola.

“The resources have been flowing, the preparations have been extensive and we are taking this storm very, very seriously,” Florida Governor Ron DeSantis told a press briefing.

Mandatory evacuation orders are in effect in several Florida counties, but the impacts are expected to spread over a wide swathe of the southeastern United States, with hurricane-force winds up to 100 miles inland.

Those staying put are advised to hunker down in safe rooms and prepare for long power outages.

Storm surge combined with the tide is expected to flood normally dry areas, with the NHC warning that water could reach as high as nine feet (2.7 metres) around the Alabama-Florida border.

Rainfall of four to eight inches (10-20 centimetres) was predicted in the most impacted zones, with localised totals of up to 15 inches.

Flash and urban flooding is expected throughout the region, and rivers could also break their banks.

At least two airports in northwestern Florida have suspended operations.

President Donald Trump is scheduled to attend Saturday’s college football game between the University of Georgia and the University of Alabama in Tuscaloosa, Alabama, but said this week he will “let the hurricane determine” his travel plans.

Isaias’s late arrival is largely due to an El Nino of historic strength.

El Nino, the warm phase of the El Nino-Southern Oscillation (ENSO), creates strong vertical wind shear over the Atlantic that tends to tear storms apart.

“We have been seeing basically nearly record strong shear throughout the Atlantic Basin this year, and that is consistent with what we’d expect to see with a strong El Nino event,” Michael Fischer of University of Miami’s Rosenstiel School of Marine, Atmospheric and Earth Science told AFP.

In the Pacific, it has the opposite effect, weakening shear and giving storms room to grow. The Pacific has already produced several hurricanes this year, some of which hit maximum category five strength.

Meanwhile, sea surface temperatures across the Gulf are running at nearly 30C, said Fischer, “basically as warm as any year we’ve seen over the last 40 years or so”.

“Sea surface temperatures in the Gulf of Mexico are in record territory because of fossil fuel-driven climate change,” Marc Alessi, a climate scientist with the Union of Concern Scientists, told AFP. “Isaias was able to tap into all of that energy in the ocean to develop into a major hurricane.”

Isaias has disrupted oil and gas production in the Gulf of Mexico, with platforms and rigs evacuated.

As of Friday, about 71 per cent of the region’s oil production had been temporarily halted, taking nearly 1.5 million barrels a day off the market, according to the Marine Minerals Administration (MMA). About 59 per cent of gas production was also suspended.