(Updates location and wind speed)
MIAMI, Oct 23 (Reuters) - Tropical Storm Sandy was expected to become a hurricane on Wednesday as it approaches the south coast of Jamaica, the U.S. National Hurricane Center said, prompting authorities on the Caribbean island to close schools and prepare shelters to take in residents of flood-prone areas.
The storm was centered about 195 miles (315 km) south of the Jamaican capital, Kingston, late on Tuesday evening and had top sustained winds of 60 miles per hour (95 km per hour).
Forecasters said a tropical storm watch might be issued for south Florida on Tuesday night or Wednesday morning, but the storm did not pose a threat to the Gulf of Mexico, where U.S. oil and gas operations are clustered.
A hurricane warning was in effect for both Jamaica and Cuba, meaning residents should expect heavy rains and strong winds within 48 hours, although forecasters said Sandy is expected to be only a weak Category One hurricane on the five-step Saffir-Simpson scale of hurricane intensity, with winds topping out at 80 mph (128 kph).
Computer models showed Sandy was on a projected path that would cut across the middle of Jamaica near the capital, Kingston, and the popular north coast resort of Ocho Rios, before passing over eastern Cuba and the Bahamas.
Sandy is expected to dump as much as 6 to 12 inches (15 to 30 cm) of rain across parts of Jamaica, Haiti, the Dominican Republic and eastern Cuba, with as much as 20 inches (50 cm) possible in some places, forecasters said. (Writing by David Adams; Editing by Sandra Maler and Lisa Shumaker)