By Jane Sutton
MIAMI, June 6 (Reuters) - Tropical Storm Andrea strengthened slightly just before making landfall in Florida on Thursday and was forecast to drench much of the U.S. Southeast with heavy rain as it cuts across Georgia and up the Atlantic coast, the National Hurricane Center said.
The season's first Atlantic tropical storm had already spawned tornadoes in Florida and threatened to fuel more twisters on Thursday night, after making landfall over the Big Bend area, where the Florida peninsula joins the mainland.
By late Thursday afternoon, Andrea was packing top sustained winds near 65 miles (100 km) per hour and it was expected to weaken after landfall, as it cuts a soggy path across the peninsula into the Atlantic, the Miami-based National Hurricane Center said.
It said the winds extended outward up to 140 miles (220 km) from the storm's center.
Andrea will likely remain a tropical storm for a day or two, hugging the shore and bringing heavy rain and gales to Georgia, South Carolina and North Carolina, said Jack Beven, a hurricane specialist at the National Hurricane Center.
"It might be just inland and it might be just a little off shore," Beven said. "It's going to be a weather-maker" as it moves north up the East Coast.
On Saturday, Andrea was expected to merge with a frontal system and morph into a Nor'easter as it moved over the northeastern U.S. coast and Nova Scotia.
Andrea posed no threat to U.S. energy interests in the Gulf of Mexico.
Tropical storm warnings were in effect for much of Florida's Gulf Coast and for the U.S. Atlantic Coast from northern Florida to Virginia, including the lower Chesapeake Bay.
The storm's outer bands buffeted Florida's west coast beginning early on Thursday and multiple tornadoes touched down across the state, including one that ripped a roof off a restaurant in Gulfport.
Another damaged several houses in the Acreage and Loxahatchee communities in Palm Beach County and sent a tree crashing through the roof of a house, injuring a woman inside.
"We had one that was hopping and skipping around in extreme western Broward and Palm Beach County," said Bob Ebaugh, a specialist at the National Weather Service in Miami. "As far as we know it was out over unpopulated areas but it did touch down several times."
The Sunshine Skyway Bridge over Tampa Bay was closed due to high winds and several Tampa-area high schools had to move their graduation ceremonies indoors because of heavy downpours.
Florida could get up to 6 inches (15 cm) of rain, while coastal areas along part of the Gulf of Mexico could see a storm surge, the forecasters said.
There were scattered power outages in the state, with at least 3,700 customers losing service.
The Atlantic hurricane season runs from June 1 to Nov. 30.
The U.S. government's top climate agency warned in an annual forecast last month that this year's season could be "extremely active" with 13 to 20 tropical storms, seven to 11 of which are expected to become hurricanes.
Three of the six hurricanes could become major at Category 3 or above, with winds of more than 110 mph (177 kph), the National Oceanic and Atmospheric Administration said.