MIAMI - Tropical Storm Wilma formed today in the northwestern Caribbean, tying the record for the most storms in an Atlantic season and following a path that some forecasters believe could menace the Gulf Coast next week as a hurricane.

Wilma is the 21st named storm of the season. The only other time that many storms have formed since record keeping began 154 years ago was in 1933.

At 8 a.m., Wilma had top sustained wind near 40 mph, just above the threshold for tropical storms. It was centered about 205 miles southeast of Grand Cayman and drifting south near 5 mph, but was expected to turn to the southwest or west within the next day.

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 are expected within 24 hours, also was posted. The storm is expected to bring 4 to 6 inches of rain in the Cayman Islands and Jamaica, with as much as 12 inches possible in some areas, National Hurricane Center forecasters said.

Long-term forecasts show the storm heading into the Gulf of Mexico by the weekend. Forecasters said high water temperatures and other conditions were favorable for it to become a significant hurricane.

But hurricane specialist Stacy Stewart said Wilma had shifted west of its previous path and could hit Mexico's Yucatan Peninsula. "At this time it doesn't appear it will be a major threat to the United States during the next five days," Stewart said.

But Wilma is then expected to re-emerge into the Gulf and could become a threat to the southern U.S.

"Usually when a storm gets into the Gulf, it's going to hit somewhere," said hurricane center meteorologist Larry Lahiff. "Where, that's too early to tell right now. Some models take it west, some take it north."

The U.S. Gulf Coast was already battered this year by Hurricanes Katrina, Rita and Dennis.

Since 1995, the Atlantic has been in a period of higher hurricane activity. Scientists say the cause of the increase is a rise in ocean temperatures and a decrease in the amount of disruptive vertical wind shear that rips hurricanes apart. Some researchers argue that global warming fueled by man's generation of greenhouse gases is the culprit.

Forecasters at the hurricane center say the busy seasons are part of a natural cycle that can last for at least 20 years, and sometimes up to 40 or 50. They say the conditions are similar to those when the Atlantic was last in a period of high activity in the 1950s and 60s.

The six-month hurricane season ends Nov. 30. Wilma is the last on the list of storm names for 2005; there are 21 names on the yearly list because the letters q, u, x, y and z are skipped. If any other storms form, letters from the Greek alphabet would be used, starting with Alpha. That has never happened in roughly 60 years of regularly named Atlantic storms.