"Hurricane Irma is a major and life-threatening storm and Florida must be prepared". The minimum pressure is has dropped to 937 mb, a sign of intensification.
Forecasters said Irma could strengthen to 180 mph over the next 12 hours.
The powerful hurricane could produce 10 inches of rain, cause flash floods and landslides, and create waves up to 23 feet.
The increase to 175 miles per hour winds makes Irma the strongest hurricane in the Atlantic since Hurricane Felix in 2007, according to Colorado State University researcher Phil Klotzbach.
The eye of Hurricane Irma was located near latitude 16.8 North, longitude 58.4 West, 225 miles east of Antigua and about 230 miles east-southeast of Barbuda.
Formation chance through 5 days: 70 percent.
Irma, still a Category 4 storm, is moving at 13 miles per hour.
Tropical Storm Jose forms behind Irma in Atlantic
While the Northern Caribbean states are preparing for Category 5, Hurricane Irma, which has been described as "extremely dangerous" another tropical storm, named Jose, has formed. The storm is expecting to strength and become a hurricane by Friday. "Don't freak out, but focus on your hurricane plan and preparations for any kind of impact".
It is not expected to threaten the northern Gulf Coast, according to the National Weather Service. Exactly where this turn will occur, whether it is west of the Peninsula, east of it, or right up the spine is yet to be determined.
After impacting the Leeward Islands and Puerto Rico, there remains some uncertainty as to where Irma will go, but Tuesday will be seeing model consistency over more westward track and an eventual turn toward Florida.
States of emergency have been declared in Puerto Rico and the U.S. Virgin Islands, AP reported.
One was christened Tropical Storm Jose on Tuesday morning.
Irma's future, and that of the US coastline, is dependent on two atmospheric features: the Bermuda High and an upper-level low moving west to east through the central U.S.