Tropical Storm Sally formed Saturday off south Florida, becoming the earliest 18th-named storm on record in an Atlantic hurricane season as it headed toward the Gulf of Mexico amid signs of strengthening further.

Sally emerged from a tropical depression swirling off the tip of Florida, on a forecast track bound for the Gulf. It was expected to become a hurricane by late Monday that could threaten a wide swath of the northern Gulf coast early in the week. It becomes the earliest 18th named storm in a busy tropical season, beating Stan, which formed on Oct. 2, 2006.

The National Hurricane Center in Miami said Sally would dump heavy rain around the Florida Keys and the southern and western parts of the state. Maximum sustained winds were clocked at 40 mph (65 kph) with higher gusts. Additional strengthening is expected over the coming days.

An Air Force Hurricane Hunter plane was scheduled to investigate the system later Saturday afternoon.

“Since the system will be traversing very warm waters and through a moist air mass with moderate vertical shear for the next few days, steady strengthening is anticipated,” forecasters wrote in their 2 p.m. EDT advisory.

Sally was located 35 miles (60 kilometers) south-southeast of Naples on Saturday afternoon, according to National Hurricane Center said. The system was moving to the west at 7 mph (11 kph). A tropical storm watch is in effect from the Ochlockonee River to the Okaloosa/Walton County Line.

The storm is currently expected to bring 2 to 4 inches (5 to 10 centimeters) of rain to parts of Florida, with isolated totals up to 6 inches (15 centimeters). Meteorologists warn of an increasing risk of life-threatening storm surge and dangerous hurricane-force winds from southeastern Louisiana to the Alabama coast.

Meanwhile, Tropical Storm Paulette had maximum sustained winds at 70 mph (110 kph) and was 510 miles (820 kilometers) southeast of Bermuda, where a hurricane watch and tropical storm warning are in effect. Forecasters said Paulette would become a hurricane later Saturday and drop up to 6 inches (15 centimeters) of rain on the territory through Monday, adding that it is expected to be a “dangerous hurricane” when it is near Bermuda on Sunday night and Monday.

Tropical Storm Rene weakened in recent hours and was reclassified as a tropical depression. It had maximum sustained winds at 35 mph (55 kph) and was 1,225 miles (2,020 kilometers) east-northeast of the Northern Leeward Islands. Forecasters said Rene wasn’t expected to strengthen and did not pose any threat to land.