Hurricane Irma - Dangerous threat for Florida, Southeast

by Weather.com on 6 Sep 2017 Weather com has produced this accurate and detailed account of the latest with Irma as she builds in the Caribbean to become a Cat5 storm and gets set to unleash fury in the region.

Hurricane Irma, a dangerous Category 5 hurricane, is nearing the island of Barbuda, an island of 1600 residents, with 185 mph sustained winds and higher gusts. Irma will rake through the Virgin Islands, Puerto Rico, Hispañola, the Bahamas and Cuba before posing a serious threat to Florida and parts of the Southeast beginning this weekend.

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Irma became the strongest hurricane in the Atlantic basin, outside of the Caribbean Sea and Gulf of Mexico, on record on Tuesday morning, according to the National Hurricane Center.

Below is everything we know about Irma right now, including its latest status, along with potential forecast impacts in the U.S. and the Caribbean Islands.

Irma's Latest Status, Timing

The center of Irma is located less than 50 miles east-southeast of the island of Barbuda and is moving west-northwestward at about 15 mph. This is a change in forward movement as a slight right turn has taken place, but not enough for impacts to be lessened in the northern Leeward Islands.

Irma's maximum sustained winds are steady at 185 mph based on data from NOAA and Air Force Hurricane Hunter aircraft. Based on wind speed, Irma is the strongest Atlantic hurricane since Wilma in 2005 which also had maximum sustained winds of 185 mph.

Additionally, Irma is just the 5th Atlantic hurricane to have maximum sustained winds of 185 mph or greater, according to Dr. Phil Klotzbach, a tropical scientist at Colorado State University. Hurricane Allen occupies the top spot with 190 mph winds in 1980.

Hurricane warnings have been issued for the northern Leeward Islands, Puerto Rico, the Virgin Islands and for the northern coast of the Dominican Republic. This includes Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, Sint Maarten, St. Martin, St. Barthelemy, Guadeloupe, Vieques and Culebra.

Additionally, a tropical storm warning is in effect for Dominica and for the southern coast of the Dominican Republic from Cabo Engano westward to the border with Haiti.

A hurricane watch is also in effect for the north coast Haiti from the border with the Dominican Republic to Le Mole St. Nicholas, the Turks and Caicos Islands and the southeastern Bahamas. A hurricane watch has also been issued for Cuba from Matanzas Province eastward to Guantanamo Province.

Low wind shear, increased mid-level moisture and ample oceanic-heat content favor that Irma will remain a powerful hurricane Category 4 or stronger) for the next several days, though some intensity fluctuations are likely at times. At this intensity, small deviations in wind speed will not change impacts. A direct hit will be catastrophic.

For the next five days, Irma will move west-northwest on the south side of a ridge of high pressure called the Bermuda high, centered in the central Atlantic.
(Interactive MAP: Track Irma)

By this weekend, Irma will begin to turn north in the direction of a departing southward dip in the jet stream that will set up in the eastern United States. Where that northward turn occurs will be critical for what impacts Irma may bring to parts of the southeastern United States.

Here's a general overview of the timing for impacts from Irma into this weekend.

Potential Impact Timing

• Leeward Islands: Wednesday; tropical storm-force winds will arrive by sunrise.
• Puerto Rico/Virgin Islands: Wednesday- early Thursday; tropical storm force winds will arrive during the early morning hours
• Dominican Republic/Haiti: Thursday; tropical storm force winds will arrive Wednesday night or on Thursday
• Turks and Caicos: Late Thursday-Friday
• Bahamas: Friday-this weekend
• Cuba: Friday-this weekend
• Southeast United States: This weekend into early next week, beginning in south Florida Saturday

U.S. Forecast: Watching Florida, Southeast Closely

While it is still too soon to narrow down specifics on the exact path of Irma's center and eyewall, there is an increasing chance of a major hurricane strike on at least part of South Florida, including the Florida Keys, this weekend.

As mentioned before, the vast majority of the forecast guidance indicates Irma will begin to turn more to the north sometime this weekend.

The strength and expansiveness of the Bermuda-Azores high over the Atlantic Ocean and the timing, depth and location of a southward dip in the jet stream near the eastern U.S. will dictate where and when that northward turn occurs.

(More: Why the U.S. Forecast is Uncertain)

According to the latest NHC forecast, the center of Irma may be very close to South Florida by Sunday morning, with conditions going downhill already during the day, Saturday and worsening for southwest Florida on Sunday.

However, as the NHC reminds us, average errors in the track of the center of an Atlantic tropical cyclone 4 to 5 days out are between 175 and 225 miles, which can make a large difference in impacts.

For now, all residents along the Southeast coast and eastern Gulf Coast, including Florida, Georgia and the Carolinas, should monitor the progress of Irma closely.

In addition, Irma's wind field will be large, therefore, dangerous surf and coastal flooding will likely exist throughout the southeastern U.S. coastline even well away from Irma's center by late week.

No matter what the future holds for Irma's path and intensity, the NHC advises, 'Everyone in hurricane-prone areas should ensure that they have their hurricane plan in place, as we are now near the peak of the season.'

Forecast: Leeward Islands, Puerto Rico, Hispaniola, Cuba, Bahamas

Leeward Islands

Irma will make a direct hit on the northern Leeward Islands overnight into early Wednesday morning as a Category 5 hurricane, the strongest to hit that area since Lenny in 1999. Islands that are most likely to take a direct hit by the eyewall of Irma are Barbuda, Saint Barthelemy, Saint Martin and Anguilla through early Wednesday morning.

Hurricane-force winds (74-plus mph) are expected within the hurricane warning area of the Leeward Islands early Wednesday, and tropical-storm-force winds (39-plus mph) are arriving in Antigua and Barbuda.

Destructive winds, capable of widespread tree damage, long-lived power outages, and structural devastation can be expected. Storm-surge flooding, high surf and rip currents will also be dangers, and heavy rain could contribute to flooding and mudslides, as well.

The NHC says that a storm surge of 7 to 11 feet above normal tide levels is possible in the extreme northern Leeward Islands near and north of where the center tracks. Battering waves will ride atop the surge, capable of additional damage and erosion at the coast.

Rainfall totals in the Leeward Islands may total 8 to 12 inches, with locally 20 inches in spots, especially in elevated spots.
Conditions should improve by Wednesday night.

Puerto Rico and the Virgin Islands

It will be a very close call whether the eyewall of Irma, containing the highest, most destructive winds, will track over the Virgin Islands and northern Puerto Rico.

Regardless of that, hurricane-force winds (74-plus mph) are expected in the hurricane warning area by late Wednesday, with tropical-storm-force winds (39-plus mph) beginning early Wednesday.

The NHC says that a storm surge of 7 to 11 feet above normal tide levels is possible in the Virgin Islands, except St. Croix.

Additionally, a storm surge of 3 to 5 feet is possible along the northern coast of Puerto Rico, along with a storm surge of 1 to 2 feet along the southern coast of Puerto Rico and St. Croix.

Heavy rain bands are also likely to affect Puerto Rico and the Virgin Islands, which may result in flooding and mudslides. Rainfall may total 4 to 10 inches, with locally 15 inches in spots.

Conditions should improve quickly by later Thursday morning.

Hispañola, Turks and Caicos, Bahamas and Cuba

Irma will likely pass near Hispañola, the Turks and Caicos, the Bahamas and Cuba late this week into the weekend as a major hurricane.

Also, keep an eye on weather for more information and up to the minute intel, as well as to read this item in full

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