MIAMI, Fla. -- You can expect unpleasant weather throughout the day as Tropical Storm Arlene spins off rain, rough seas and wind to South Florida.

All of South Florida is under a flood watch until 10 p.m. tonight. The rain will likely continue into Saturday, but the weather should begin a gradual clearing on Sunday.

Forecasters said Arlene could become a weak hurricane before hitting land late Saturday. Hurricane watches were posted from Panama City to the Louisiana-Mississippi border for Arlene, the Atlantic season's first tropical storm. It had top sustained winds of 60 mph, up from 45 mph earlier in the day.

The downpour that landed on Havana and the rest of western Cuba as Arlene passed the island's westernmost tip early Friday was welcome relief from the island's severe drought. Flooding was possible because it could drop 5 inches of rain or more, meteorologists said, and some schools were closed, but there were no immediate reports of damage.

Arlene was expected to make landfall in the United States around midnight Saturday, most likely somewhere between eastern Louisiana and the western Florida Panhandle, with the worst weather east of the storm's center.

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It could cause tornados in southwestern Florida and the Florida Keys, meteorologists said. Beach erosion was also possible.

"This is going to be a major rainfall event before and ahead of the storm," said Trisha Wallace, a hurricane center meteorologist.

At 11 a.m. EDT, Arlene's poorly defined center was about 470 miles south-southeast of Pensacola. The storm was moving north at about 13 mph, the National Hurricane Center in Miami said. Wind and rain extended 150 miles to the north and east from the storm's center.

The hurricane watch extends from the mouth of the Pearl River to Panama City, Fla. A tropical storm warning was in effect for the U.S. Gulf Coast from Grand Isle, La., to St. Marks, Fla. A tropical storm warning was also in effect for the Dry Tortugas, a cluster of islands about 70 miles west of Key West that are a U.S. national park.

The Panhandle was battered last year by Ivan, one of the four hurricanes to strike Florida in the space of a few weeks. State meteorologist Ben Nelson warned coastal residents that flooding patterns could be different now "because the dunes, the offshore structures, have been changed around by Ivan."

Hurricane season began June 1 and ends Nov. 30. In addition to Ivan, Florida was struck by Charley, Frances and Jeanne. The storms caused about 130 deaths in the United States and are blamed for $22 billion in insured damage.