Tropical Storm Bertha strengthens in Atlantic

MIAMI (Reuters) - Tropical Storm Bertha strengthened a little on Friday as it spun in the open Atlantic Ocean far from land, forecasters at the U.S. National Hurricane Center said.

Bertha's top winds grew to 50 mph (85 kph), up from 45 mph (72 kph) on Thursday, and forecasters said it could gradually strengthen further over the next few days.

At 11 a.m. EST the second tropical storm of the 2008 Atlantic hurricane season was about 385 miles west of the Cape Verde Islands and was moving west-northwest about 16 mph (26 kph).

It was expected to stay on that path for two or three days and then curve northwest on a track that would keep it over the open sea.

Some computer forecasting models predicted Bertha's top winds would reach the 74 mph (119 kph) threshold to become a hurricane in three or four days, though the hurricane center's official forecast keeps its strength just below that mark.

Energy markets closely monitor tropical storms in the Atlantic because of the potential for them to strengthen into hurricanes and threaten oil installations in the Gulf of Mexico.

Long-range computer predictions did not foresee Bertha making it into the Gulf of Mexico or anywhere near the U.S. coast. It was still more than 2,000 miles away from the easternmost Caribbean islands.

The Atlantic-Caribbean hurricane season runs from June 1 to the end of November, with August and September usually the busiest months.

Bertha's formation off the African coast near the Cape Verde islands could be an unwelcome portent of the season ahead.

It is unusual for storms to form so far east so early in the year. And when they do form in that area in June or July, total storm activity for the year tends to be at least average and often above average, according to the National Oceanic and Atmospheric Administration.

(Reporting by Jane Sutton; Editing by Eric Beech)