The Tropical Storm Watch has been upgraded to a Warning, and a Hurricane Watch is now in effect for Jamaica as Melissa slowly drifts across the central Caribbean Sea.

This means tropical storm conditions pose a possible threat to Jamaica within 36 hours and hurricane conditions are likely to pose a threat within 48 hours.

At 4:00 a.m. the centre of Tropical Storm Melissa was about 353 kilometres south-southeast of Morant point, Jamaica or about 390 kilometres south-southeast of Kingston.

Tropical Storm Melissa is moving very slowly toward the west near 6-km per hour.

Little change in strength is forecast during the next day or so but, Melissa could become a hurricane in a couple of days, with more substantial intensification forecast by late Friday and through the weekend.

On the forecast track, tropical storm melissa is expected to continue in the direction of

Jamaica before turning towards the west on Saturday and moving over the waters south of the island.

As the system nears Jamaica, showers will begin to affect the island with periods of moderate to heavy rainfall beginning late this afternoon. This will continue through Friday and the weekend.

Strong, gusty winds, possibly reaching tropical storm strength, are expected to gradually develop late today and Friday, continuing into the weekend.

These winds will initially affect eastern and southern parishes, before gradually spreading across the remainder of the island.

Winds reaching hurricane strength are possible over sections of eastern parishes as early as Saturday, as Tropical Storm Melissa continues to move closer to Jamaica.