Catastrophic Hurricane Irma — now a Cat 5 — is on a collision course with Florida By Brian McNoldy and Jason Samenow September 5 at 2:05 PM

Catastrophic Hurricane Irma — now a Cat 5 — is on a collision course with Florida
By Brian McNoldy and Jason Samenow September 5 at 2:05 PM

Hurricane Irma takes aim at Florida

Capital Weather Gang's Jason Samenow tells us what to expect from Hurricane Irma on Tuesday, Sept. 5. (Monica Akhtar/The Washington Post)

This story has been updated.

Hurricane Irma is an “extremely dangerous” Category 5, barreling toward the northern Lesser Antilles and Southern Florida. It’s already the strongest hurricane ever recorded outside the Caribbean and the Gulf of Mexico, and it’s likely to make landfall somewhere in Florida over the weekend.

If it does, the impact could be catastrophic.
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The storm is life-threatening for the United States, including Puerto Rico, the U.S. and British Virgin Islands, the Dominican Republic, Haiti, Cuba and the southeastern Bahamas. Hurricane warnings have been issued for the northern Leeward Islands, Virgin Islands, and Puerto Rico. A hurricane watch is in effect for Hispaniola and southeastern Bahamas.

With maximum winds of 185 mph, Irma is tied for the second strongest storm ever observed in the Atlantic. And in its Tuesday morning discussion, the National Hurricane Center said the storm is in an environment “ideal for some additional intensification.”
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Hurricane Irma barrels toward Caribbean, southern U.S.
Hurricane Irma, a powerful Category 5 storm, plowed toward the Caribbean and the southern United States on Sept. 5 with residents in its path braced for possible life-threatening winds, storm surges and flooding. (Reuters)

[How to prepare for Hurricane Irma]

The hurricane is expected to remain at least a Category 4 for the next few days with minor fluctuations in intensity. It could even become slightly stronger, but it is already nearing historical precedent and a theoretical limit for how strong it can get.

It cannot be overstated that Hurricane Irma is extremely dangerous and will produce the full gamut of hurricane hazards across the Caribbean and potentially in South Florida, including a devastating storm surge, destructive winds and dangerous flash flooding.

All of Florida — especially South Florida and the Keys — should be preparing for a major hurricane landfall on Sunday. Tropical-storm-force winds are expected to arrive as soon as Friday.


Mainland U.S. landfall threat

Computer models are in strong agreement that by Saturday, Irma will be approaching the Florida Keys — where dangerous storm conditions are likely. Then, they show a sharp northward turn by Sunday morning. The precise timing and location of the turn has huge implications for Florida.

Model ensemble guidance out to 10 days from the European model (top) and the U.S. model (bottom). (B. Tang, UAlbany)

It is impossible to say with certainty whether Irma will track up along the eastern side of the Florida peninsula, the western side, or straight up the peninsula. Since the weekend, models have generally shifted westward with the storm’s forecast track, which means interests along the coast of the Gulf of Mexico should also closely monitor this storm.

[Florida declares a state of emergency in response to Irma]

For a major hurricane, the exact track of the storm’s eyewall — the zone surrounding its calm center — is critical as it will determine where the most severe effects tend to concentrate. The most violent winds coincide with the eyewall, and the biggest storm surge occurs just to its right (or north).

But as Irma is such a large and powerful hurricane, very dangerous weather will also occur up to 200 miles away from the eyewall — including coastal surge, flooding rains and potentially damaging winds.

“The hurricane force winds in Irma are wider than Florida,” tweeted Bryan Norcross, hurricane specialist at the Weather Channel. “You won’t need a direct hit to get Wilma-type winds & storm surge on both coasts.”

Beyond the weekend, the scenarios really depend on which side of Florida it tracks. But for now, it’s safe to say that the southeast United States, including the Florida panhandle, Georgia and the Carolinas, should also brace for potential impacts, such as flash flooding, storm surge and strong winds.

Seven-day cumulative rainfall forecast. (NOAA/WPC)

Impact on the Leeward Islands, Virgin Islands and Puerto Rico

At 2 p.m. Tuesday, the powerhouse storm was positioned 180 miles east of the island of Antigua in the northern Leewards, where it is forecast to make a direct impact early Wednesday. The storm was moving westward at 14 miles per hour.

Destructive winds as well as heavy rain that can produce flash flooding and mudslides are possible in the warning areas. Along the coast, the storm surge height – or rise in water above normally dry air – could reach 7-11 feet – especially just north of the storm center.

Irma is likely to become the strongest hurricane on record to hit the Leeward Islands, even more intense than David, which raked across the central Leeward Islands in 1979. “David was a horrible hurricane for Leeward Islands: 56 fatalities in Dominica,” tweeted Phil Klotzbach, hurricane expert at Colorado State University.

Antigua, Barbuda, Saint Kitts and Anguilla — in particular — are right in the path of the storm.

“Really feel for the northern Leeward Islands,” tweeted National Hurricane Center forecaster Eric Blake. “A hurricane this strong there only comes around once a generation or two.”

Areas affected by the core winds near the storm’s eye face devastating wind destruction. The Hurricane Center provides this description of the 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.

After passing the northern Leeward Islands, the hurricane will strike the British Virgin Islands with potentially catastrophic effects.

The U.S. Virgin Islands and Puerto Rico may remain south of the storm’s center, so less prone to Irma’s most hostile conditions. But even so, damaging winds and torrential rains are likely.

Irma’s place in history

Irma’s peak intensity so far 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 miles per hour. It is tied for second most intense with Hurricane Wilma in 2005, Hurricane Gilbert in 1988 and the 1935 Florida Keys hurricane.

Here's where #Irma currently ranks on the list of strongest Atlantic Hurricanes on record. Oddly high pressure compared to the others. pic.twitter.com/sD0m7h3tDW

— Brad Panovich (@wxbrad) September 5, 2017

If Irma makes landfall as a Category 4 or higher in the United States, joining Hurricane Harvey, it will become the first time two storms so strong struck the United States in the same season.

Tropical Storm Jose forms in eastern Atlantic

While all attention is on Hurricane Irma, Tropical Storm Jose formed in the eastern Atlantic Tuesday morning. This storm is also predicted to intensify into a hurricane over the coming days, but the latest track forecast keeps it away from land areas for the most part.

(National Hurricane Center)