(CNN) -- Hurricane Wilma jumped from a Category 2 to a dangerous Category 5 storm in mere hours Wednesday, with maximum sustained winds of 175 mph -- and possibly the lowest recorded barometric pressure, the National Hurricane Center said Wednesday.

The storm -- located in the western Caribbean -- was forecast to make landfall somewhere in southwestern Florida as soon as the weekend.

As of 5 a.m. ET, an Air Force reconnaissance plane reported a pressure of 884 millibars in Wilma's eye -- below the record of 888 millibars in 1988's Hurricane Gilbert. (Watch forecast for Hurricane Wilma to turn toward Florida -- 1:16)

Lower pressure is one indicator of a more intense hurricane.

The hurricane center in Miami, Florida, cautioned, however, that the measurement cannot be an official record low until instruments and calculations are calibrated, which will happen after Wilma fades.

Meanwhile, forecasters warned that Wilma is a "catastrophic" Category 5 storm -- the highest category on the Saffir-Simpson scale of hurricane intensity. It strengthened within a matter of a few hours -- at 1 a.m. ET, the hurricane center reported the storm had 150 mph winds, taking it from a Category 2 to a Category 4. Just 90 minutes later, the center reported Wilma had maximum sustained winds of 175 mph and higher gusts.

The long-range forecast has Wilma weakening to a Category 3 by Saturday, before hitting the United States. Due to the erratic nature of hurricane movement, such long-term forecasts often change.

Year's third Category 5
Wilma is the third Category 5 storm this year, preceded by Hurricane Katrina, which killed thousands when it slammed into the Gulf Coast on August 29, and Hurricane Rita, which followed weeks later.

The center said it did not know if that was a record because it does not track the number of Category 5 hurricanes in a season.

Wilma, however, did tie two other records Tuesday -- that of the most hurricanes in a season: 12; and the most named storms in a season: 21.

At 5 a.m. ET, the center of the storm was located 170 miles south-southwest of Grand Cayman Island and about 365 miles southeast of Cozumel, Mexico. It was moving west-northwest at nearly 8 mph and is expected to turn to the northwest over the next 24 hours, the hurricane center said.

A Category 5 hurricane can cause a storm surge of 18 feet above normal and catastrophic damage.

Projections for Wilma's path suggest the storm may skirt the western tip of Cuba on Friday, possibly as a Category 4 storm with winds of greater than 130 mph, before curving eastward and barreling toward the southwestern Florida coast.

"All interests in the Florida Keys and the Florida peninsula should closely monitor the progress of Wilma," the NHC said.

Hurricane-force winds extend outward about 15 miles from the eye, and tropical-storm-force winds stretch up to 155 miles from the center.

Cuban hurricane watch
Cuba has issued a hurricane watch for the provinces of Matanzas westward through Pinar del Rio and for the Isle of Youth, according to the hurricane center. Late Tuesday, Mexico extended a hurricane watch for the Yucatan Peninsula. The watch area now stretches from Punta Gruesa to Cabo Catoche. A hurricane watch means hurricane conditions, including winds of at least 74 mph, are possible within 36 hours.

A 150-mile stretch of the Honduran coast is under a tropical storm warning, and the Cayman Islands are under tropical storm warning and a hurricane watch.

The hurricane center said Cuba could get anywhere from 10 to 15 inches of rain in Wilma's wake, with some areas getting socked with as much as 25 inches. Additional rainfall accumulations of of up to 10 inches, with up to 15 inches possible in some areas, was possible across the Cayman Islands and Jamaica through Thursday. Across the Yucatan Peninsula, rainfall of up to 6 inches was possible, with up to 12 inches in some areas.

Wilma is the 21st named storm of the 2005 hurricane season and the 12th to reach hurricane status. Of those, five have developed into major hurricanes.

The only other time 12 hurricanes have been recorded in the Atlantic was in 1969, according to the hurricane center. The most major hurricanes in a year was eight, in 1950.

Wilma is also the final name on the 2005 list. The hurricane center does not use some letters of the alphabet, including X, Y and Z.

If any tropical storms and subsequent hurricanes form before the season ends on November 30, they will be classified using the Greek alphabet, beginning with Alpha.

If that happens, it would be the first time since the naming of storms began in 1953, according to the hurricane center.