George Town, Cayman Islands ? A tropical storm warning was in effect Sunday for the Cayman Islands as a tropical depression moved through the Atlantic on a path that could threaten the U.S. Gulf Coast later this week as a hurricane, forecasters said.

The system was expected to become Tropical Storm Wilma today, which would make it the 21st named storm of the season, tying the record for the most storms in an Atlantic season, the National Hurricane Center in Miami said.

At 10 p.m. CDT, the depression was centered about 155 miles southeast of Grand Cayman, forecasters said.

Long-term forecasts show the storm would likely move west and north, putting the storm in the Gulf of Mexico on Thursday or Friday. Forecasters said water temperature and other conditions were favorable for it to become a significant hurricane.

“Once storms get into the Gulf of Mexico, I’m aware of only one storm on record that dissipated. It has almost nowhere to go except land somewhere,” hurricane specialist James Franklin said in Miami.

A hurricane watch was issued for the Cayman Islands, meaning hurricane conditions could be felt there within 36 hours. A tropical storm warning, meaning tropical storm conditions within 24 hours, also was posted.