By Jane Sutton
MIAMI, Oct 4 (Reuters) - Tropical Storm Karen churned through the Gulf of Mexico on Friday, disrupting U.S. energy output on its way to drenching the coast from Louisiana and the Florida Panhandle, the U.S. National Hurricane Center said.
Energy companies in the Gulf shut down production and evacuated workers from offshore platforms as the storm approached a region that produces nearly a fifth of daily U.S. oil output.
Oil prices have been dropping amid concerns that a prolonged U.S. government shutdown would hurt demand, but the losses were limited as the storm in the Gulf curbed supply. Brent futures fell below $109 a barrel, then edged back up above that mark on Friday.
The governors of Louisiana, Mississippi and Florida declared states of emergency to speed storm preparations, and the Federal Emergency Management Agency recalled some furloughed workers to assist.
Karen weakened slightly overnight and had top winds of 60 miles (95 km) per hour on Friday morning.
It was centered about 275 miles (445 km) south-southwest of the mouth of the Mississippi River and was moving north-northwest. The storm was expected to turn north and then northeast, hitting the coast on Saturday, forecasters at the Miami-based hurricane center said.
The intensity forecast was "rather problematic" because an area of low pressure in the atmosphere and a decrease in wind shear could allow it to strengthen to just below hurricane strength, especially if it makes the northeast turn while it is still over water, senior hurricane specialist Jack Bevin wrote.
It would become a hurricane if its sustained winds hit 74 mph (119 kph).
Coastal residents may start feeling the effects by Friday night. On its current track, the storm's center was expected to cross the coastline near the Louisiana-Mississippi border by late on Saturday.
The storm was expected to dump up to 8 inches (20 cm) of rain in its path and to push a surge of seawater over the shoreline.
"The highest water will occur along the immediate coast near and to the east of where landfall occurs, where the surge will be accompanied by dangerous waves," the forecasters said.
A hurricane watch was issued for the coast from Grand Isle, Louisiana, south of New Orleans, to Destin, Florida, alerting residents to expect hurricane conditions within 48 hours.
A tropical storm watch was in Florida from Destin to Indian Pass and in Louisiana from west of Grand Isle to east of Morgan City. The watch area included metropolitan New Orleans, Lake Maurepas and Lake Pontchartrain. Tropical storms carry winds of 39 mph to 73 mph (63 kph to 118 kph).