Cuba, the eastern Bahamas and Turks and Caicos also lie in the expected path of the storm, which will make its way north and east towards Bermuda later this week.

The hurricane is expected to stay well offshore of the United States, bringing only rough surf and minor coastal flooding to the U.S. East Coast.

On Monday at midday (1600 GMT), Melissa was still 145 miles (230 km) southwest of Kingston, Jamaica, and about 330 miles (530 km) southwest of Guantánamo, Cuba, according to the NHC in Miami.

The hurricane was creeping west at just 3 mph (5 kph), the center said, but would likely make a north-northeastward turn through Jamaica late on Monday and into Tuesday.

The storm's slow movement over unusually tepid Caribbean water had contributed to its ballooning size and strength, the center's forecasters said, threatening Jamaica with days of never-before-seen catastrophic winds and as much as 3 feet of rain.

"This will result in extensive infrastructural damage, long-lasting power and communication outages, and isolated communities," the NHC said.

Nearby Haiti and the Dominican Republic have already faced days of torrential downpours leading to at least four deaths, authorities in those island nations said.

Damian Anderson, a teacher from Hagley Gap, a town nestled in Jamaica's soaring Blue Mountains, said impassable roads had already cut off his community.
"We can't move," Anderson, 47, said. "We're scared. We've never seen a multi-day event like this before."

Jamaica has seen many large hurricanes in the past, including Category 4 Hurricane Gilbert in 1988, but a direct hit from a Category 5 would be unprecedented, said Evan Thompson, of Jamaica's Meteorological Service.

Category 5 is the highest on the Saffir-Simpson scale with sustained winds exceeding 157 mph (250 kph). 

CUBA PREPARATIONS
Much of the eastern half of Cuba also battened down ahead of the storm's expected landfall late on Tuesday.

Cuban authorities said they had evacuated upwards of 500,000 people living in coastal and mountainous areas vulnerable to heavy winds and flooding.

On Monday, authorities cancelled schools, buses and trains until further notice across eastern Cuba ahead of the storm's arrival. The hurricane was not expected to directly impact the capital Havana.   

(Reporting by Zahra Burton in Kingston and Dave Sherwood in Havana; writing by Dave Sherwood; Editing by Nia Williams)