The NHC said Isabel's maximum sustained winds have increased to 240 kilometers an hour (149 miles an hour) as it bears west at 15 kilometers an hour (nine miles an hour).

At 1500 GMT, the eye of the hurricane was located 865 kilometersmiles) to the east-northeast of the Leeward Islands on the eastern fringe of the Caribbean.

If Isabel continues along its current path, the hurricane is expected to hit seas to the north of Puerto Rico by the weekend.

Isabel's effects are likely to be felt along the Puerto Rican and Virgin Islands coastlines in the next couple of days, the NHC warned.

The Bahamas island group and the East Coast of the United States could also be affected by Isabel in the coming week, although this depends on the hurricane's future trajectory.

Isabel's winds have risen to between 220 and 240 kilometers an hourand 149 miles an hour), and the hurricane is classed as a Category Four hurricane on a scale of one to five, with five being the most severe.

For a hurricane to be classified as Category Four on the Saffir-Simpson scale, its winds have to rage between 210 kilometers an hour (130 miles an hour) and 249 kilometers an hour (155 miles an hour).

"Fluctuations in strength are common in major hurricanes, and these could occur during the next 24 hours" with Isabel, the NHC warned.

The hurricane season, which runs from June 1 to November 30, has been more active than normal this year and has already witnessed six to nine hurricanes, according to the National Oceanic and Atmospheric Administration (NOAA).

NOAA calculated that two to four storms had developed into Category Three hurricanes.

Isabel is the second massive hurricane of 2003 to hit the Caribbean, following close on the heels of Hurricane Fabian, which ravaged Bermuda last week.

Four people are still missing from Bermuda and the authorities are still clearing up the physical damage from Fabian's passing.

TERRA.WIRE