Forecasters issued hurricane watches Monday as Hurricane Helene, a combination of several storms in the Cayman Islands, is set to devastate the southern US as shown in a weather map shared by the National Hurricane Center.

The disturbance is forecast to become Hurricane Helene on Wednesday as it approaches the Gulf Coast, according to the U.S. National Hurricane Center in Miami.

“It could certainly become a major hurricane, which is Category 3,” Brad Reinhart, a senior hurricane specialist at the center, said in a phone interview. “People in the Florida Panhandle and the west coast of Florida certainly need to pay close attention.” Florida Gov. Ron DeSantis declared a state of emergency in 41 counties ahead of the expected hurricane.

Reinhart said it’s too early to forecast where it might make landfall. He warned “there’s always some potential” for it to strengthen into a Category 4 storm, but said it might not be the most likely outcome. He said the disturbance could become a tropical storm by Tuesday, and that tropical storm conditions could affect parts of Florida on Wednesday as it approaches.

It could turn into a major hurricane by the time it reaches the northeast Gulf Coast on Thursday. “It’s a pretty aggressive forecast for intensification over the next few days,” he said. “People need to remain on high alert.”

Very warm sea temperatures are forecast to fuel formation of a tropical storm, which is forecast to quickly strengthen into a hurricane thanks to favorable conditions that include a moist atmosphere, which supports thunderstorm developments, and light upper-level winds at more than 10,000 feet (around 3,000 meters), Reinhart said.

The cluster of storms was about 115 miles (185 kilometers) west-southwest of Grand Cayman early Tuesday. It had maximum sustained winds of 35 mph (55 kph) and was moving northwest at 6 mph (9 kph).

A hurricane watch was in effect for the Cuban province of Pinar del Rio and eastern Mexico from Cabo Catoche to Tulum. A tropical storm warning was in effect for Grand Cayman; eastern Mexico from Rio Lagartos to Tulum; and for the Cuban provinces of Artemisa, Pinar del Rio and the Isle of Youth. A tropical storm watch was in effect for Florida’s Dry Tortugas and the Lower Keys south of Seven Mile Bridge.

“While it is too soon to pinpoint the exact location and magnitude of impacts, the potential for life-threatening storm surge and damaging hurricane-force winds along the coast of the Florida Panhandle and the Florida west coast is increasing,” the center said in a statement.

Up to 8 inches of rain is forecast for western Cuba and the Cayman Islands with isolated total of some 12 inches (30 centimeters). Up to 4 inches (10 centimeters) of rain is expected for the eastern Yucatan Peninsula, with isolated total of more than 6 inches (15 centimeters) inches.

Heavy rainfall also is forecast for the southeast U.S. starting on Wednesday, threatening flash and river flooding, according to the National Hurricane Center. Up to 6 inches (15 centimeters) of rain was forecast for the region, with isolated totals of 10 inches (25 centimeters).

Meanwhile, up to 4 feet (1.2 meters) of storm surge is forecast for parts of Cuba and Mexico. On Monday, authorities in the Cayman Islands closed schools as forecasters warned of heavy flooding associated with the disturbance, which is due to cut a path between Cuba and Mexico’s Yucatan Peninsula late Tuesday night.

The Cayman Islands was already experiencing elevated tides unrelated to the cluster of storms, and waves of up to 10 feet (3 meters) are expected, said Shamal Clarke with the Cayman Islands Weather Service. “Flooding will become an issue for a lot of residents,” he said.

Helene would be the eighth named storm of the Atlantic hurricane season which runs from June 1 to Nov. 30. The National Oceanic and Atmospheric Administration has predicted an above-average Atlantic hurricane season this year because of record-warm ocean temperatures. It forecast 17 to 25 named storms, with four to seven major hurricanes of Category 3 or higher.