U.S. weather forecasters say Hurricane Wilma has strengthened to a powerful category 5 storm and a key low-pressure measurement indicates it is the most powerful storm of the year.

A statement from the U.S. National Hurricane Center says reconnaissance aircraft tracking the storm reported one of the lowest pressure measurements ever recorded. Lower pressure is one indicator of a more intense hurricane.

Forecasters say Wilma is 270 kilometers south of Grand Cayman and continues moving northwest at about 13 kilometers per hour.

Hurricane Wilma, the 12th such storm of the season, is on course to sideswipe Central America or Mexico and looming as a threat Florida by the weekend

Hurricane watches and a tropical storm warnings remain in effect for the Cayman islands and points west.

Officials say early projections show Wilma is likely to enter the Gulf of Mexico between the Yucatan Peninsula and Cuba before heading towards the southwestern Florida coast later this week.