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Category 2 Hurricane Dorian headed towards the Southeast U.S. after pounding the Bahamas

By Dr. Jeff Masters From Weather Underground

Above: Aerial video from Great Abaco Island begins to provide an idea of how widespread the destruction from Dorian is. Image credit: Brandon Clement, @wxchasing.

Dorian finally made its north-northwestward turn towards the Southeast U.S. late Tuesday morning, after subjecting the northwestern Bahamas to the most extreme pounding of any populated place in the history of Atlantic hurricanes.

Dorian made landfall on Great Abaco Island in The Bahamas at 12:40 pm Sunday as a Category 5 hurricane with 185 mph winds, making it the strongest landfalling Atlantic hurricane on record (tied with the 1935 Labor Day Hurricane in the Florida Keys). The eyewall of the Category 5 hurricane then moved over the eastern end of Grand Bahama Island near 9 pm EDT Sunday. Portions of the eyewall lashed Great Abaco and Grand Bahama islands with Category 5 winds for a total of 22 hours before the great hurricane finally weakened to Category 4 strength. In records going back over a century, there are no cases where an Atlantic Category 5 hurricane has impacted a land area for as long as Dorian battered The Bahamas.

#Dorian‘s incredible stall over the island of Grand Bahama appears to set a new record for the slowest moving major hurricane over any 24-hour period since records began in 1851.

Most people can easily walk faster than the mere 1.3 mph (2.0 kph) that Dorian has been advancing.— Robert Rohde (@RARohde) September 3, 2019

For a total of 36 hours, ending near 9 am EDT this morning, Dorian pummeled Grand Bahama Island while at major hurricane strength, with winds of 115 – 185 mph. During the first 14 hours of that period, Dorian was essentially stationary while at Category 5 strength. Damage on Grand Bahama and Great Abaco Island is going to be some of the most extreme ever seen from a hurricane–similar to what a 20-mile wide EF3 or EF4 tornado would do. Imagine what it would be like to endure a 14-hour period of Cat 5 winds accompanied by flying debris, the insane shriek of the wind, a 20-foot storm surge and 20+ inches of rain. The people that lived through it are going to need substantial mental health services to address their PTSD issues, not to mention a massive disaster relief response. Prayers for the people of The Bahamas!

#HurricaneDorian has affected Bahamas heavily on Monday, with vast areas hit with #flooding, including the Grand Bahama International Airport, Freeport. ICEYE#SAR satellite image from 11:44AM local time. Please, stay safe! (Y: coastline. W: roads. Source: OpenStreetMap.)— ICEYE (@iceyefi) September 2, 2019

The only official weather station on Grand Bahama Island is at Settlement Point on the extreme northwestern end. At noon EDT Tuesday, Settlement Point reported sustained winds of 53 mph, gusting to 63 mph, with a pressure of 991 mb. The station has experienced tropical storm-force winds since 10 pm Sunday night. We don’t have any rainfall measurements in the northwest Bahamas, but satellite estimates from NASA indicate that up over 30” of rain may have fallen over portions of Grand Bahama and Great Abaco islands.

Figure 1. Estimated precipitation from the Melbourne, Florida radar from Dorian as of 12:11 pm EDT September 3, 2019. Rainfall amounts in central Florida were mostly less than an inch, with a few bands of 1 – 2 inches.

Dorian’s long-anticipated journey towards the Southeast U.S. coast has begun

After what seems like an eternity, Dorian has finally moved away from Grand Bahama Island, and hurricane-force winds had mostly pulled away from the island at long last. As of 11 am EDT Tuesday, Dorian was a Category 2 hurricane with 110 mph winds, centered about 45 miles north of Freeport on Grand Bahama, and was moving northwest at 2 mph—a speed that should pick up gradually over the next 24 hours.

While Dorian’s weakening is welcome news, it has come with an expansion of the hurricane’s wind field, which is unwelcome news for the Southeast U.S. coast. At 11 am EDT Tuesday, Dorian had hurricane-force winds that extended out about 45 miles to the northwest of the center, and tropical storm-force winds that extended out about 150 miles. NHC predicted that Dorian’s hurricane-force winds would expand outward by about 10% by Wednesday.

Figure 2. The eye of Hurricane Dorian as photographed from the International Space Station by Nick Hague on September 2, 2019

Forecast for Dorian

By Wednesday, Dorian should be east of the Florida/Georgia border and begin a gradual turn toward the northeast. Dorian’s weakening trend may be put on hold briefly as land interaction decreases and Dorian crosses the warm waters of the Gulf Stream, so Dorian is expected to be a high-end Category 2 storm through at least Thursday morning.

A very small fraction of the 0Z Tuesday European and GFS model ensemble members bring Dorian along the coast of Georgia and South Carolina, but landfall in eastern North Carolina on Thursday night is a more likely scenario, based on strong model consensus. Even so, tropical-storm-force winds are likely to affect the entire coast from central Florida northward, and such winds can bring down trees and power lines. Dorian may also bring Category 1 hurricane-force winds to the eastern part of Nova Scotia and Newfoundland, Canada, as it races northeastward on Saturday. Keep in mind that the center of a hurricane will track outside the warning cone about one-third of the time, and evacuate if recommended or mandated! See the NHC website for the latest hurricane and storm surge watches and warnings, which will be revised frequently as Dorian works its way up the coast.

Figure 3. WU depiction of NHC forecast track for Dorian as of 11 am EDT Tuesday, September 3, 2019.

Inland rainfall will probably not be as widespread from Dorian as with some hurricanes of similar strengths and paths, because Dorian is not being steered by a strong upper trough and because the hurricane will not be crossing a strong preexisting frontal zone. Inland flooding along the coastal zone will remain a serious threat, though, and it could exacerbate any storm surge flooding in estuaries and coastal rivers. We can expect widespread 4 – 10” rains within about 50 miles of the coast, with localized totals above 10”. Inland rains may be more extensive in southeastern North Carolina, though amounts in general are not expected to match the mammoth, destructive totals seen in storms like Matthew (2016) and Florence (2018).

Dorian is growing larger, and given its longevity and trajectory, it could pack more storm surge than one might assume from its Saffir-Simpson category (a storm’s strength rating is only very loosely associated with the surge it produces). We are fortunate Dorian will not be making a landfall perpendicular to the coast—the worst trajectory for surge—but 2016’s Hurricane Matthew provides a good sense of what is possible from Dorian.

Comparison with Hurricane Matthew of 2016

The consensus track for Dorian bears a close resemblance to that of 2016’s Hurricane Matthew, which caused an estimated $11 billion in U.S. damage as it curled very near the coast from Florida to North Carolina on a coast-hugging track. The latest NHC forecast has Dorian following Matthew’s track within about 20 miles, all the way from central Florida to South Carolina. Dorian is slightly larger than Matthew was, and will be moving about twice as slowly on average, which will allow the hurricane more time to pile up a large storm surge that will last over multiple high tide cycles. Dorian is likely to be somewhat weaker than Matthew was, though—Matthew maintained Category 3 strength until reaching the waters offshore from the Florida/Georgia border. Dorian is already at Category 2 strength and is likely to be at Cat 2 strength during most of its traverse of the Florida coastal waters.

Overall, storm surge damages from Dorian in the Southeast U.S. are likely to be roughly similar to those of Hurricane Matthew, amounting to at least $1 billion.

A CC Kelvin Wave is forecast to pass over the east Atlantic & Africa next week at the climatological peak of the hurricane season. This could lead to a parade of tropical cyclones in the east-central Atlantic. Odds are #Dorian may not be the last threat to landmasses further west— Eric Webb (@webberweather) September 3, 2019

There’s more: The tropics are aflame with activity

While we still have Dorian to deal with, there are several other systems in the Atlantic and elsewhere that deserve mention.

—Tropical Storm Fernand formed on Tuesday afternoon in the far western Gulf of Mexico, about 185 miles east-northeast of Tampico Mexico. It’s expected to make landfall as a tropical storm late Wednesday on Mexico’s northeast Gulf Coast. Very heavy rains—6 to 12 inches, with isolated 15” amounts—could produce dangerous mudslides and flash floods from the coast into the higher terrain of the Sierra Madre Oriental. The system is not expected to be close enough to South Texas for significant impacts there.

—A tropical wave west of the Cabo Verde Islands (Invest 91L) became Tropical Depression Eight at 5 pm Tuesday and is predicted by NHC to become Tropical Storm Gabrielle by Wednesday. All of the ensemble members from the 0Z Tuesday run of the GFS model, and about half of the European ensemble members, make 91L a tropical storm. The good news is that this would be a fish storm, heading northwest toward the unpopulated waters of central North Atlantic. Hurricane strength appears unlikely. The next name on the Atlantic list is Gabrielle.

—Another disturbance (Invest 92L) is located several hundred miles south of Bermuda, well east of Dorian, heading northward. Sea surface temperatures ahead of this system are unusually warm (28-29°C or 82-84°F, about 1-2°C above average). About a third of GFS ensemble members, but only about 10-20% of Euro members, develop 92L into a tropical storm. Wind shear is expected to keep any development modest as the system heads past Bermuda into open waters.

—The Atlantic system of most concern will emerge off the coast of Africa in a few days. This system, which was being given 5-day odds of development of 70% by NHC, has the potential to be a long-track Cape Verdes-type tropical cyclone that may make it across the Atlantic to eventually threaten land.

Figure 4. Visible-wavelength satellite image of Hurricane Juliette at 1500Z (11 am EDT) Tuesday, September 3, 2019. Image credit: RAMMB/CIRA/CSU.

—In the Northeast Pacific, Hurricane Juliette rocketed to high-end Category 3 strength overnight about 500 miles southwest of Cabo San Lucas, Mexico. Juliette brought sustained winds of 99 mph and gusts to 130 mph to Clarion Island, a Mexican Navy outpost. Juliette may touch Cat 4 strength before weakening as it moves atop colder waters well offshore.

—In the Northwest Pacific, Typhoon Lingling could strike the Korean peninsula as a Category 2 storm this weekend, and Tropical Storm 14W may threaten Japan as a typhoon early next week.

Bob Henson co-wrote this post.

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