The Capital Weather Gang's Jason Samenow tells you what to expect from Hurricane Irma as it continues to barrel toward the U.S. mainland on Wednesday, Sept. 6. (Monica Akhtar/The Washington Post)

(This story, first posted on Wednesday, was updated Thursday morning.)

For nearly two days, monstrous Hurricane Irma has sustained Category 5 winds of at least 180 miles per hour while ripping through the northern Lesser Antilles and Virgin Islands. The storm, tied for the second-strongest ever recorded in the Atlantic Ocean, is headed for the southeastern Bahamas and, by the weekend and early next week, Florida and the Southeast United States.

“The threat of direct hurricane impacts in Florida over the weekend and early next week continues to increase,” the National Hurricane Center said early Thursday. It added hurricanes watches would be issued for parts of the Florida Keys and Florida Peninsula late Thursday morning.

This is a life-threatening storm that the Hurricane Center warns is capable of catastrophic damage. Preparations should be rushed to completion along and near its projected path, including over South Florida.

At 5 a.m. Thursday, the storm was 95 miles north of Punta Cana, Dominican Republic and was barreling to the west-northwest at 17 mph, moving away from both Puerto Rico and the Virgin Islands. Its peak winds were estimated at 180 miles per hour, a slight decrease in strength from Wednesday.

The storm’s heavier rain bands which had been lashing Puerto Rico into Wednesday evening had retreated to the northwest and just scattered showers lingered Thursday morning. In a bit of fortunate news, the storm’s eyewall, the region with the most destructive winds, had passed to its north.

With the storm heading west-northwest, hurricane warnings were in effect for the Dominican Republic, the Turks and Caicos, Haiti and the Bahamas. A hurricane watch covered Cuba.

(National Hurricane Center)

This historically intense hurricane, which maintained winds of 185 miles per hour longer than any storm ever recorded on Earth, is forecast to modestly weaken in the next two days, but remain an extremely dangerous Category 4 or 5 storm. It will produce the full gamut of hurricane hazards across the Bahamas and potentially South Florida, including a devastating storm surge, destructive winds and dangerous flash flooding.

Meanwhile, two new hurricanes formed late Wednesday afternoon in the Atlantic basin: Jose in the eastern Atlantic Ocean and Katia in the southwest Gulf of Mexico (see more information down below).

Irma’s growing threat for the mainland U.S.

Model forecasts have shifted the center of Irma’s track eastward since Tuesday, projecting its core to pass right along Florida’s east coast. But enough uncertainty in the track exists that all of Florida should be on the highest alert and preparing for this hurricane.

Some of the computer simulations on Wednesday tracked the storm center very near Southeast Florida Sunday morning, which would present a very dangerous situation for the Miami to Fort Lauderdale area. However, shifts in the storm track are likely.


Model simulations of the center of Irma at 2 p.m. Sunday. (WeatherBell.com)

Tropical-storm-force winds are likely to arrive in Florida on Saturday, with the worst storm conditions occurring Sunday. The most extreme conditions are likely to occur near the storm center, but it is impossible this far out to pinpoint exactly where that will track. And serious storm effects will expand well outside the center.

The entire Florida peninsula is only about 100 miles wide, small compared to the size of the storm. Tropical-storm-force winds presently extend outward up to 185 miles from the storm center and hurricane-force winds extend 50 miles away.

A hurricane does not need to be rated Category 5 intensity to cause catastrophic damage. Remember, the category rating only refers to the peak winds in the eyewall, not the size of the storm, the rainfall and the storm surge.

Group of simulations from American (red) and European (blue) from Wednesday night.. (StormVistaWxModels.com)

Locations in northern Florida as well as up into Georgia and the Carolinas should also be preparing for a significant impact Monday and Tuesday. The forecasts from recent model runs bear some resemblance to Hurricane Matthew, which affected these areas just 11 months ago.

The rainfall forecast for the coming week shows a heavy swath over the Florida peninsula, and then spreading northward into the Carolinas as Irma likely tracks over those areas early next week.

National Weather Service 7-day rainfall forecast.(WeatherBell.com)

Impact on the Virgin Islands and Puerto Rico

Wednesday afternoon, the storm’s eye had moved over Virgin Gorda in the British Virgin Islands and its southern eyewall (the region of most powerful winds) raked Saint Thomas in the U.S. Virgin Islands.

Early Wednesday afternoon, a wind gust to 131 miles per hour was clocked on Buck Island and 87 miles per hour on St. Thomas in the U.S. Virgin Islands. The National Weather Service issued an extreme wind warning for destructive winds gusts over 115 miles per hour for Saint John and Saint Thomas, “producing swaths of tornado-like damage.” A flash flooding warning was also issued.

Areas affected by the storm’s eyewall likely faced high destructive winds. The Hurricane Center provides this description of the potential damage inflicted by Category 5 winds:

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.

Hurricane Irma heads toward Puerto Rico on Sept. 6, after slamming the northern Leeward Islands with torrential rains and howling winds. (CIRA/RAMMB/NOAA)

Forecasts also called for rainfall totals of 8-12 inches along the path, with isolated amounts up to 20 inches, leading to flash flooding and mudslides — especially over any high terrain.

While the center of Irma passed just north of Puerto Rico, a  wind gust of 63 miles per hour was clocked in San Juan early Wednesday evening and up to 900,000 power outages were reported. In Culebra, Puerto Rico, a small island 17 miles east of the mainland, a wind gust registered 111 miles per hour during the afternoon.

As the storm passes just north of the Dominican Republic and Haiti on Thursday, hurricane-force winds and torrential rains are possible.

Later on Thursday, the storm will near the Turks and Caicos and southeastern Bahamas, where it could push ashore a devastating storm surge of 15 to 20 feet above normally dry land.

Irma’s path through the Northern Lesser Antilles

Tuesday night and Wednesday morning, the hurricane passed directly over Barbuda and Saint Martin in the northern Leeward Islands, the strongest hurricane ever recorded in that region and tied with the 1935 Florida Keys hurricane as the strongest Atlantic storm to strike land.

Gaston Browne, the prime minister of Antigua and Barbuda, toured the extensive damage caused by Hurricane Irma on Sept. 6. (ABS TV Antigua)

As Barbuda took a direct hit, the weather station there clocked a wind gust to 155 mph before it went offline. The storm surge on the island, or the rise in water above normally dry land, reached at least 8 feet.

Widespread destruction was reported on the island.

The storm also passed directly over Anguilla and St. Martin early Wednesday, causing severe damage.

Hurricane Irma brought widespread flooding and electrical blackouts to the islands of St. Barthelemy and St. Martin on Sept. 6, the French government said. (PTZtv.com)

Irma’s place in history

Irma’s peak intensity (185 mph) ranks among the strongest in recorded history, exceeding the likes of Katrina, Andrew and Camille — whose winds peaked at 175 mph.

Among the most intense storms on record, it only trails Hurricane Allen in 1980, which had winds of 190 mph. It is tied for second most intense with Hurricane Wilma in 2005, Hurricane Gilbert in 1988 and the 1935 Florida Keys hurricane.

A US Air Force Reserve hurricane hunter flight got a clear view of Hurricane Irma's eyewall on Sept. 5. The storm intensified to a Category 5. (Maj. Brad Roundtree/USAFReserve)

The storm has maintained maximum wind speeds of at least 185 mph longer than any other storm on Earth in recorded history.

Late Tuesday night, its pressure dropped to 914 millibars (the lower the pressure, the stronger the storm), ranking as the lowest of any storm on record outside the Caribbean and Gulf of Mexico in the Atlantic basin.

The storm has generated the most Accumulated Cyclone Energy, a measure of both a storm’s duration and intensity, of any hurricane on record.

Without a doubt, the World Meteorological Organization will retire the names Harvey and Irma after this season. While there have been several instances of consecutive storm names getting retired (Rita and Stan 2005, Ivan and Jeanne 2004, Isabel and Juan 2003, Luis and Marilyn 1995), the U.S. has only been hit by more than one Category 4+ hurricane in a season one time: 1915. Two Category 4 hurricanes hit in Texas and Louisiana six weeks apart that year.

Credit to tropical weather expert and occasional Capital Weather Gang contributor Phil Klotzbach for some of the statistics in this section.

Hurricanes Jose and Katia

While Irma is grabbing all of the attention, two other hurricanes are spinning in the Atlantic basin:

  • Tropical Storm Jose was upgraded to a hurricane late Wednesday afternoon. Positioned far out in the eastern Atlantic Ocean, the storm was rapidly gaining strength and was forecast to become a major Category 3 storm by Friday. The current track forecast keeps it mostly away from land areas over the next couple of days but brings it close to the same islands in the northeastern Lesser Antilles slammed by Irma this weekend and forecasters will be watching it closely.
  • Tropical Storm Katia, which formed early Wednesday in the southwestern Gulf of Mexico, intensified quickly into a hurricane late Wednesday afternoon. It could intensify into a Category 2 hurricane before making landfall in the Mexico state of Veracruz Friday into Saturday, where a hurricane warning is in effect.

Hurricane season in perspective

In terms of Accumulated Cyclone Energy for all storms so far, 2017 has spiked to well above average in the past week thanks to Irma. And now we also have Jose and Katia adding to the tally.  As of Wednesday morning, this season’s Accumulated Cyclone Energy is at about 152 percent of average for the date.