MIAMI -- As Florida braced for what seemed like an inevitable hit from Hurricane Wilma, Tropical Storm Alpha made landfall Sunday in the Dominican Republic. It was later downgraded to a tropical depression

At 5 p.m. EDT, the storm had sustained winds near 35 mph and was moving north-northwest at 18 mph, the National Hurricane Center in Miami said. The storm may briefly regain tropical-storm status before dissapating by Tuesday.

"(Alpha) is not going to be a threat to the United States," National Hurricane Center Director Max Mayfield said. "I want to make that very clear."

Alpha formed Saturday in the Caribbean Sea, setting the record for the most named storms in an Atlantic hurricane season, forecasters said.

It is the season's 22nd tropical storm, the most since record keeping began in 1851. This is the first time a letter from the Greek alphabet has been used because the list of storm names was exhausted. The previous record of 21 storms stood since 1933.

"We've gone through the list of 21 and we've started with the Greek alphabet," Mayfield said. "We are just hoping we don't have to use any more of those Greek letters."

Wilma, meanwhile, took a turn toward Florida early Sunday and was expected to strike the southern part of the state Monday. The U.S. Gulf Coast has already been battered this year by Hurricanes Katrina, Rita and Dennis.

The storms are part of a record hurricane season which has seen an increase in storm activity as part of a cycle that started in 1995 and is expected to last at least another 10 years.

Scientists believe 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 argue that global warming created by man's generation of greenhouse gases is to blame.

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.