Bonnie weakens to tropical depression over Florida

MIAMI (Reuters) - Tropical Storm Bonnie weakened as it slogged across south Florida on Friday, prompting U.S. forecasters to downgrade the system to a tropical depression as it took aim at the energy-rich Gulf of Mexico.

The U.S. National Hurricane Center reclassified the short-lived tropical cyclone after its top sustained winds decreased to near 35 miles per hour.

There was a chance Bonnie could regain tropical storm strength as it moves out over the Gulf of Mexico on Friday evening, but the Miami-based hurricane center said the current environment in the Gulf made that unlikely.

The storm has been on a track expected to take it over the site of BP Plc's deepwater oil spill after its trek across Florida.

At 5 p.m. EDT (2100 GMT), the center of the fast-moving storm was located about 35 miles south of Ft. Myers, Florida, and it was moving west-northwest at 18 miles per hour, the hurricane center said.

Oil and natural gas producers in the energy-rich Gulf were evacuating offshore workers earlier on Friday, and the U.S. government said 28.3 percent of Gulf oil production and 10.4 percent of gas output had been shut down ahead of the storm.

Two rigs drilling relief wells intended to permanently plug BP's deepwater Gulf oil gusher were preparing to move out of Bonnie's path on Friday.

The evacuation could push back BP's mid-August target date for ending the worst oil spill in U.S. history, but the blown-out Macondo well will remain capped during the halt in operations.

The Gulf of Mexico is home to about 30 percent of U.S. oil production, 11 percent of natural gas production and more than 43 percent of U.S. refinery capacity.

Bonnie, which had packed top sustained winds of about 40 miles per hour, doused much of south Florida with heavy rains as it moved across the peninsula earlier on Friday.

There were no reports of significant damage or storm surge, however, and the possibility of isolated tornadoes over the southern tip of Florida late on Friday posed the biggest local threat from the storm.

With only a slight chance of intensification, Bonnie was not expected to become a hurricane. It was due to make landfall again anywhere between the Louisiana coast and Florida's northwest Panhandle early on Sunday morning.

Bonnie was the second named storm of the Atlantic hurricane season, which began on June 1 and runs through November 30.

Forecasters say this year's hurricane season is expected to be especially active.

(Reporting by Tom Brown, editing by Peter Cooney and Todd Eastham)