Dennis Menaces Cuba, Keys

High waves crash to the shoreline of the Guantanamo Bay Naval Station, Cuba, Thursday, July 7, 2005. Strong winds from Hurricane Dennis blew across the U.S. prison camp for terror suspects causing minor damage and a spectacular view of the heaving surf but only slightly disrupting operations at the high-security base. (AP Photo/Andres Leighton)
People in the Florida Keys were ordered to flee and residents along hundreds of miles of Gulf Coast began boarding up Thursday as a rapidly strengthening Hurricane Dennis took aim at the storm-weary region.

Forecasters warned residents from Florida to Louisiana to be ready this weekend for Dennis, with top winds already at 135 mph. The hurricane turned into a Category 4 storm Thursday evening as it gained strength while barreling through the Caribbean toward the Gulf of Mexico.

At 8 a.m. EDT, Dennis' center was about 230 miles southeast of Havana, Cuba, and about 285 miles south-southeast of Key West, Florida. It was moving northwest at about 12 mph, but was expected to pick up speed and hit central Cuba later in the day.

"At this stage, it appears it will be the strongest landfall for Cuba ever in the month of July," said National Hurricane Center deputy director Ed Rappaport on CBS News' The Early Show.

Forecasters expect Dennis to hit the straits of Florida overnight, with the center passing near or just west of the lower Florida Keys, where there is now a hurricane warning in effect.

Landfall on the northeastern Gulf Coast is expected late in the weekend.

"Right now, it's category 4 intensity. We think there will be a little weakening over Cuba, but then re-strengthening is possible," Rappaport told co-anchor Russ Mitchell. "We think we'll have a major hurricane passing by the Florida Keys, probably still a major hurricane, category 3 perhaps, maybe a little bit stronger when landfall occurs on the mainland late this weekend."

Many in the hurricane's projected path already got a wake-up call this week from a surprising Tropical Storm Cindy that caused three deaths, knocked out power to thousands, and spawned twisters that toppled trees and caused up to $40 million damage to a famed NASCAR track.

"We're trying to get ready for whatever happens. We've been through so much already," Jose Davila said as he painted a house in Port Charlotte, where blue tarps still dot the rooftops of homes waiting to be repaired from Hurricane Charley, the first of a record four hurricanes to hit Florida last year.