MIAMI —  A subtropical depression formed Saturday in the open Atlantic, prompting Bermuda (search) to issue a tropical storm watch.

The system could strengthen into Tropical Storm Vince (search) later in the day, according to the National Hurricane Center (search) in Miami. Vince would be the 20th named storm in one of the busiest hurricane seasons on record.

At 2 p.m. EDT, the depression's center was about 385 miles southeast of Bermuda. It was moving toward the west-northwest at about 15 mph. It had top sustained winds of about 35 mph, but was expected to strengthen even if it didn't become a tropical storm, forecasters said.

Long-term forecasts showed the system either reaching the United States mainland in about five days, or curving farther out to sea after passing Bermuda. But hurricane specialist Jack Beven (search) said it appears the system might not survive if it gets closer to the U.S. because of other weather in the area.

"It's really too early to say just how much of a threat this will pose to the U.S. But right now, it's not too great of a threat," he said.

The depression's strongest winds are far from its center, but if they start closing in on its core it could strengthen into a storm, said Robbie Berg, a hurricane center meteorologist.

The Atlantic hurricane season began June 1 and ends Nov. 30. The current one is tied for the second-busiest since record keeping began in 1851. The record is 21 tropical storms and hurricanes in 1933.

After Vince, only one name is left for storms this season — Wilma. After that, storms are named after letters in the Greek alphabet. That has never happened before in more than 50 years of regularly naming storms.