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Category 5 Irma stays on perilous path toward Florida; hurricane watch issued

Hurricane Irma as seen from space on Sept. 6 at 1:45 p.m. EDT.

NASA

By JASON SAMENOW AND BRIAN MCNOLDY | The Washington Post | Published: September 7, 2017

Hurricane Irma, the massive, record-setting Category 5 hurricane, continues to track toward South Florida, where it could deliver a devastating blow. Before it hits Florida, it may well leave behind catastrophic damage in parts of the Bahamas and Turks and Caicos. By early next week, South Carolina could well be in the storm's cross hairs.

Meanwhile, two other hurricanes were intensifying in the southwest Gulf of Mexico and eastern Atlantic.

But Irma, positioned 120 miles southeast from Grand Turk Island, is the most pressing concern. As it charged to the west-northwest at 16 miles per hour, the National Hurricane Center issued hurricane watches Thursday morning for the Florida peninsula from Jupiter Inlet southward and around the peninsula to Bonita Beach, including the Florida Keys.

A storm surge watch was issued for the same area of Florida due to the potential for water to rise well above normally dry land at the coast as the storm approaches.

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"The threat of dangerous major hurricane impacts in Florida continues to increase," the Hurricane Center said Thursday morning.

Closer to the storm's immediate location, hurricane warnings were in effect for the Dominican Republic, Haiti, and the Bahamas.

The storm, packing maximum sustained winds of 175 miles per hour, has maintained Category 5 winds (157 mph+) for two entire days now. As it remains clear of large land masses, which would disrupt the storm, and passes over some of the warmest water in the world (nearly 90 degrees), significant weakening is unlikely. The National Hurricane Center predicts Irma will remain a powerful Category 4 or 5 hurricane as it approaches Florida.

This historically extreme hurricane, which maintained winds of 185 miles per hour longer than any storm ever recorded on Earth, 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.

The Hurricane Center is urging residents of Florida to rush preparations to completion.

Potential effects on Florida and the Southeast U.S.

In South Florida, this storm is being taken as deadly serious. Coastal areas are being evacuated, shelters established, and food and gas supplies have dwindled. Although there is uncertainty in the track and the exact path of the violent eyewall, where winds are the strongest, it will be difficult for the state to avoid a disaster, it's just a matter of how severe.

Tropical-storm-force winds are expected to reach South Florida by Saturday as Irma approaches from the southwest. Then, the all-important northward turn is still expected to take place early on Sunday when the storm would make landfall. Exactly where the north turn occurs is the critical question.

As of Thursday morning, the most likely scenario based on computer model guidance, was that the storm will track along or just off the east coast.

Models, however, can shift. The difference between a track just off the east coast and just off the west coast is only 150 miles and the average error in hurricane forecasts this far in advance is about that big. It is still not out of the question that Irma could track north up the west coast of the Florida peninsula or directly up the spine.

If the storm tracks up Florida's east coast, then Miami, Fort Lauderdale, West Palm Beach, Melbourne, Daytona Beach, and Jacksonville will take big hits. If it runs up the spine of the peninsula, the storm will be quicker to decay, but hurricane-force winds would reach both coasts. If it buzz saws up the west coast, then Key West, Naples, Fort Myers, Tampa, and Tallahassee would face devastating effects.

When Irma makes its closest approach to Florida - most likely early Sunday - the Hurricane Center predicts it will produce Category 3 or 4 winds. Here is its description of the kind of damage Category 4 winds would inflict:

"Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months."

Note that such extreme winds are typically confined to the eyewall which is only about 10 to 15 miles wide, which is why the exact track is important in terms of where the most severe wind damage concentrates.

Irrespective of exactly where Irma tracks, it appears inevitable that many coastal population centers in Florida will experience a devastating storm surge of 5 to 10 feet above normally dry land that will inundate roads, homes, and businesses. The biggest storm surge will occur immediately north of the storm center.

In southeast Florida, the Hurricane Center forecasts 8 to 12 inches of rain with isolated amounts to 20 inches.

Beyond Florida, there is a big risk for destructive winds and a serious storm surge up to Georgia, South Carolina, and North Carolina, but the details greatly depend on the track over Florida.

The worst case for these states would be if Irma narrowly misses the east coast of Florida, stays over warm water, and then hits them while maintaining its strength. A potential landfall along the Southeast coast would be on Monday. Models currently project South Carolina is the most likely landfall locations, but this could change.

"The chance of direct impacts is increasing in portions of Georgia, South Carolina, and North Carolina," the Hurricane Center said Thursday morning.

As the storm tracks up the Southeast coast and then inland, heavy rain will expand over a large area along with the potential for flash flooding, although it's too soon to pinpoint what areas will receive the most rain.

Effects on the Hispaniola, Turks and Caicos, Bahamas

Before Irma threatens South Florida, it is predicted to first scrape along the north coast the Dominican Republic and Haiti. The center of the storm and worst winds are predicted to remain offshore. However, these areas will be subject to damaging wind gusts and flash flooding.

Thursday night, the center of the storm may pass directly over the Turks and Caicos producing potentially catastrophic Category 5 winds and 8 to 12 inches of rain (locally up to 20 inches) of rain. The storm surge is of particular concern, as the water may rise 16 to 20 feet above normally dry land in coastal sections north of the storm center causing extreme inundation.

A devastating storm surge of 16 to 20 feet is also possible in the southeastern Bahamas Thursday night into Friday along with hurricane-force winds. The Hurricane Center also notes much of the Bahamas could see 8 to 12 inches of rain through Saturday.

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.

The storm has maintained maximum wind speeds of at least 180 mph longer than any other storm on record in the Atlantic or Pacific Ocean.

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.

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