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Isaias becomes a hurricane and is forecast to track ominously close to East Coast from Florida to Maine

Tropical storm watches have been issued for parts of the Florida coast.

The Post's Matthew Cappucci explains what East Coast states can expect as they brace for Tropical Storm Isaias, the storm drenched the Bahamas on July 31. (Video: The Washington Post)
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1:55 a.m. Friday — Isaias upgraded to hurricane

The National Hurricane Center posted a special advisory at midnight noting Isaias had intensified to hurricane strength. Packing 80 mph winds, the storm was about 45 miles southeast of Great Inagua Island in the southeast Bahamas just before 2 a.m. Friday. Isaias is moving northwest at 18 mph.

Tropical storm warnings were upgraded to hurricane warnings for the southeastern, central and northwestern Bahamas.

“Hurricane conditions and dangerous storm surge are expected in portions of the southeastern Bahamas overnight, [and over the] central and northwestern Bahamas late Friday and Saturday,” the Hurricane Center wrote.

Original article from Thursday

The forecast for Tropical Storm Isaias, the earliest ninth named storm on record in the Atlantic, has taken a dangerous turn. The tempest is now predicted to strengthen to a hurricane and sweep through the Bahamas before tracking perilously close to Florida this weekend and the rest of the East Coast next week.

Isaias has already unleashed torrential rain, flash flooding and power outages in Puerto Rico.

Understanding hurricane forecasts: making sense of spaghetti, cones and categories

Tropical storm warnings are up for much of the Dominican Republic, Haiti, and Turks and Caicos, as well as the southeastern and central Bahamas. A tropical storm watch has also been issued for the northwestern Bahamas, including the Abacos Islands, which were devastated by Category 5 Hurricane Dorian last September. The warning has been dropped in Puerto Rico and the Virgin Islands.

Strong wind and driving rain caused by Hurricane Isaias lashed Turks and Caicos overnight on July 30. (Video: Savitri Daniel via Storyful)

Meanwhile, tropical storm watches have been issued in Florida between Homestead and north of Vero Beach, as well as in Miami, Fort Lauderdale and Palm Beach. Residents in the Southeast U.S. are carefully watching the track of Isaias, with a close shave or landfall among the possibilities.

“There is a risk of impacts from winds, heavy rainfall, and storm surge this weekend along the Florida east coast and spreading northward along the remainder of the U.S. east coast through early next week,” the National Hurricane Center wrote Thursday.

Many computer models suggest the storm will parallel the coast into New England by the middle of next week. The storm’s exact track and rate of intensification, still coming into focus, will determine how severely Isaiah affects coastal zones and even areas farther inland.

The adjustments come as a result of greater clarity regarding how Isaias’s structure would evolve after encountering the high terrain of the Dominican Republic. Initially expected to be weakened, the cyclone instead reshuffled its area of rotation, allowing it to charge on relatively unscathed.

In the Sunshine State, where Isaias is expected to make its closest approach this weekend, coronavirus cases have sharply increased in the past two months, and Florida trails only California when it comes to cumulative cases. The virus makes storm preparations, particularly evacuation decisions and the opening of storm shelters, difficult due to social distancing requirements and other considerations.

On Wednesday, the state reported 9,446 new cases and 217 new deaths, making Florida the first state to exceed 200 deaths in a single day since that grim milestone was last recorded in early May. During just the past seven days, the state has logged 71,804 new cases and nearly 1,000 new deaths from the virus, according to a Washington Post database.

Florida plans to suspend covid-19 testing at all of its statewide locations beginning at 5 p.m. Thursday on account of the storm.

Isaias became the fifth named storm to form during July, tied with 2005 for the most on record and the earliest “I” storm on record by more than a week. This year has also featured the earliest-forming C, E, F and G storms on record in the Atlantic — Cristobal, Edouard, Fay and Gonzalo.

Isaias blasts Puerto Rico

Intense rains fell on Puerto Rico early Thursday, with a number of flash flood warnings in effect. San Juan was included, with 2 to 4 inches of rain estimated to have fallen through about 8 a.m. A few spots in southeastern Puerto Rico had seen closer to six inches, with bands of tropical downpours producing one- to two-inch-per-hour rainfall rates.

Significant flooding was reported in Cabo Rojo, a neighborhood in southeastern Puerto Rico, south of Mayaguez.

The wet weather is actually welcome. Roughly a quarter of the island is experiencing severe drought, according to the U.S. Drought Monitor, and 140,000 residents were facing strict water rationing at the start of July.

The stormy weather, however, has been blamed for power outages to more than 300,000 customers, according to the Associated Press.

Rainfall is likely to taper off from east to west during the evening hours Thursday into early Friday, with a few remnant downpours. Any of the lingering showers or thunderstorms may rotate, yielding a low-end tornado or waterspout risk. The National Weather Service in San Juan issued several marine warnings where possible waterspouts were detected via Doppler radar.

Isaias lopsided and ragged as center reforms

At 5 p.m. Thursday, the National Hurricane Center pinned Isaias’s center about 155 miles west-northwest of Punta Cana, Dominican Republic. Maximum sustained winds were estimated at 60 mph, though they are probably displaced to the northeast of the system’s developing new center of circulation.

Isaias was slightly better organized Thursday morning than it was Wednesday, but it was still having trouble intensifying. A look at reconnaissance data from an Air Force Reserve Hurricane Hunter aircraft revealed weak low-level winds — in some cases under 15 mph — surrounding Isaias’s attempt at a true low-level center.

However, microwave satellite imagery noted the mid-level core — detached from the initial low-level center — farther to the northeast. This mid-level center partially sidestepped the Dominican Republic, trekking through the Mona Passage between the Dominican Republic and Puerto Rico. This has allowed the storm to reorganize to the north.

Haiti and the Dominican Republic

As the tropical storm lashes Haiti and the Dominican Republic, widespread heavy rain and scattered flash flooding are possible — 3 to 6 inches in Haiti, with 4 to 8 inches in the Dominican Republic.

In Haiti, where severe deforestation has weakened the structural stability of hillsides, mudslides could be a very real danger.

Ordinarily, a ragged system would be shredded by the mountains of the Dominican Republic. But Isaias was unusual, forming a new low-level center beneath its mid-level spin on the north side of the mountainous island early Thursday afternoon. Data suggested that secondary center was becoming dominant, allowing the system to organize about it and increasing Isaias’s propensity to strengthen as it tracks up the East Coast.

Having a better-defined center also allows for more accurate computer model simulations.

Bahamas and Florida

Tropical Storm Isaias was beginning to move northwest Thursday evening toward the southeastern Bahamas. It will spend much of Friday and Saturday working up the chain of the Bahamas, where heavy rain and high winds are likely.

The system will probably accrue strength gradually, but some wind shear — a change of wind speed and/or direction with height — could slow this process Friday. Still, the National Hurricane Center is forecasting a strong tropical storm, with a 1- to 3-foot storm surge in the southeast Bahamas.

It will probably be worse in the northwest Bahamas, where the center is forecasting “a dangerous storm surge” that “will raise water levels by as much as 3 to 5 feet above normal tide levels in areas of onshore flow.”

The National Hurricane Center forecasts Isaias to achieve hurricane strength as is nears southeastern Florida on Saturday where heavy rains and flooding could occur in some areas.

While winds near the core may reach 75 mph, gusts just outside the center will range between 40 mph and 50 mph. That means subtle shifts in the storm track will have a big impact on what Florida winds up with.

U.S. East Coast

Late in the weekend into early next week, Isaias will probably begin to turn to the north and eventually north-northeast as it parallels the Southeast coast.

While it is still early, there is growing concern that Isaias could very easily surprise meteorologists, taking advantage of anomalously warm water temperatures and intensifying more than expected. Isaias is expected to be at hurricane strength as it moves up the coast, potentially coming close enough to make a landfall. The greatest chance of that occurring would be in the Carolinas.

With a dip in the jet stream to the west, Isaias will probably be scooped up near the East Coast. How far west it meanders depends on the strength of Atlantic high pressure, which will keep Isaias to its west. A stronger, farther west ridge of high pressure means Isaias tracks closer to or over the coast.

The Atlantic hurricane season is off to a record fast start and is likely to get worse

There are also increasing chances that moisture from Isaias could interact with an approaching cold front to bring heavy or even excessive rainfall in some areas along the Eastern Seaboard.

“[I]nterests along the entire U.S. east coast should monitor the progress of Isaias and updates to the forecast,” the Hurricane Center warned.

Andrew Freedman contributed to this report.