"Hurricane Irma has intensified into an extremely dangerous Category 5 hurricane," the National Hurricane Center says, citing the latest data from NOAA and Air Force hurricane hunter aircraft.
With maximum sustained winds of 185 mph, Irma is a Category 5 the most serious type of major hurricane on the Saffir-Sampson wind scale.
Irma is the strongest hurricane the NHC has ever recorded in the Atlantic basin outside of the Caribbean Sea and Gulf of Mexico, the agency says. It intensified at an even faster clip than expected, after its maximum sustained winds were measured at 175 mph early Tuesday morning.
Storm preparations are being rushed to completion in the Leeward Islands, where the first tropical-storm-force winds could arrive later Tuesday. Irma is currently forecast to hit the Virgin Islands and Puerto Rico on Wednesday before continuing on toward the Dominican Republic and Cuba.
The storm will bring "life-threatening wind, storm surge, and rainfall," the federal agency says.
As it nears land, Irma is being trailed by another storm Jose, the 10th tropical storm of the season which formed in the central Atlantic on Tuesday. Jose is expected to become a hurricane by Thursday morning and is likely to generate winds that top 100 mph, the hurricane center says.
While it's still too early to say where Irma might have the most impact on the continental United States, the NHC says, "There is an increasing chance of seeing some impacts from Irma in the Florida Peninsula and the Florida Keys later this week and this weekend."
Irma is predicted to maintain winds of at least 145 mph for the next five days.
Long-range forecast models are "in strong agreement on a sharp northward turn on Sunday morning," says Brian McNoldy, a senior research associate at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.
The exact timing of that right-hand turn is still unknown, McNoldy adds outlining a variable that he says will have "huge implications" for people in Florida. Depending on when it occurs, Irma's turn north could send the storm up either of Florida's coasts or through its center.
"Irma is an extremely impressive hurricane in both infrared and visible satellite images," the National Hurricane Center says, noting its distinct eye that is 25-30 miles wide.
The storm is moving westward at 15 mph, forcing hurricane warnings to be issued for a string of Caribbean islands:
U.S. Virgin Islands
Puerto Rico, Vieques and Culebra
Antigua, Barbuda, Anguilla, Montserrat, and St. Kitts and Nevis
Saba, St. Eustatius, Sint Maarten/St. Martin
British Virgin Islands
Dominican Republic from Cabo Engano to the northern border with Haiti
A hurricane watch has been declared in a number of areas, including Guadeloupe, Dominica, the Dominican Republic from south of Cabo Engano westward to the southern border with Haiti, the Turks and Caicos and the northern coast of Haiti.
Category 5 status means "catastrophic" damage will occur on lands touched by the hurricane, which is currently predicted to remain a major hurricane as it makes its way west toward the U.S. coast.
Jose is predicted to follow the same general path as Irma but with a slightly more northern approach in the forecast maps released by the hurricane center Tuesday morning.
Citing the expected effects of Irma, the NHC predicts Jose will build intensity for the next three days before hitting a plateau of around 105 mph on days four and five.
As Irma's track has become more defined, the governors of Florida and Puerto Rico declared pre-emptive states of emergency.
As NPR reported earlier:
" 'We have established protocols for the safety of all,' Puerto Rico Gov. Ricardo Rossello said, urging islanders to take precautions.
"Rossello said 4 to 8 inches of rain were expected, with wind gusts up to 60 mph.
"A few hours later, Florida Gov. Rick Scott issued an executive order declaring a state of emergency in all 67 counties in the state."
Here's how the hurricane center describes the damage that could result from a Category 5 hurricane:
"A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months."
The hurricane hunter aircraft that are helping to measure Irma's growth and likely path include NOAA's Gulfstream IV jet, which took off from Barbados around 1:30 p.m. ET Tuesday to launch dropwindsondes parachute equipped sensors that measure temperature, humidity and wind as they fall through storms from high altitudes.
Also being used is a Lockheed WP-3D Orion plane, which captured images from within the eye of Irma, complete with huge walls of clouds that create a "stadium effect."