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Tropical Storm Henri could impact New England as a hurricane

It would be New England’s first hurricane strike in 30 years.

Forecast for Henri via the GFS weather model. (weatherbell.com)
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New England hasn’t seen a direct strike from a hurricane since Category 2 Bob visited in 1991, but there’s a growing chance that lucky streak will end this weekend. The odds of Tropical Storm Henri, which spun offshore of Bermuda this week, riding parallel to the East Coast and directly affecting the Northeast are increasing.

Computer models have become increasingly bullish on the potential of a close shave or direct hit late Sunday into Monday. Mild waters off the coast could maintain Henri as a strong tropical storm or marginal hurricane.

The National Hurricane Center wrote early Thursday that storm surge, wind and rain impacts in the Northeast are “a distinct possibility.”

Henri was a 65 mph tropical storm as of 5 p.m. Eastern time Thursday but is primed to strengthen, and it could become a hurricane over the next day or so.

The latest storm comes as the remnants of Fred continue to work through the northern Appalachians; Grace, a borderline Category 1 storm, made landfall south of Cancún in Mexico’s Yucatán Peninsula.

If it seems like Henri suddenly entered the forecast equation late Wednesday, you’re not imagining things. Before that time, forecasters expected Henri to drift out to sea. But by midmorning Wednesday, computer models began portraying a potential scenario that would bring Henri closer to the coast — or even directly into Long Island, N.Y., Rhode Island or Cape Cod, Mass.

By Wednesday night, the National Hurricane Center shifted its forecast “cone of uncertainty” 150 miles west to reflect the evolving situation.

“Right now, it is advisable to begin preparing for a possible landfilling storm in” southern New England, wrote the National Weather Service office serving the Boston region Thursday morning.

The Northeast is one of the most densely populated swaths of real estate in North America, making every tweak to the forecast a high-stakes one. The National Weather Service is launching additional weather balloons from 26 sites in the northern and eastern Lower 48 in an attempt to improve computer modeling of Henri’s projected path. Balloons will be released every six hours instead of 12.

On Thursday evening, Henri was about 450 miles southeast of Cape Hatteras, N.C., or roughly 800 miles south of Nantucket, Mass. It was moving west at 10 mph. No watches or warnings have been issued for the U.S. mainland yet.

Satellite imagery Thursday revealed that Henri was struggling against wind shear, or a change in wind speed and/or direction with height. That was disproportionately blowing elements at the upper levels of the storm to the south-southwest and away from the center. Until that shear dwindles by Saturday night, Henri won’t have much of an opportunity to strengthen.

That said, the storm was exhibiting “convective bursts,” meaning thunderstorm activity was roiling and there is sufficient fuel to brew a meaty hurricane as soon as disruptive upper-level winds abate.

Henri will probably become a 90 mph hurricane by early Sunday as it rides north off the East Coast, where atmospheric steering currents will enter the equation. A dip in the jet stream carrying cool air at the upper levels, and reducing air pressure, will be positioned to the west, swinging over the Mid-Atlantic by Saturday. That could help “capture” Henri, guiding it due north, perhaps into southern New England.

High pressure to the east will act as a guardrail, blocking Henri from recurving, or taking a more traditional right turn, out to sea. The magnitude and position of that high-pressure force field of sorts will be instrumental in determining the exact track of Henri.

Ultimately, specific impacts won’t be able to be ironed out until confidence emerges in those two variables. A direct hit could produce wind gusts around 80 mph, a storm surge of several feet and up to 8 inches of rainfall. An offshore miss or scrape would spell more routine tropical storm conditions for the coastline, including high surf.

New England typically sees its strongest wind and most severe storms from wintertime nor’easters, but the presence of full trees brings greater vulnerability to strong winds in the summertime and could spell power outages.

A full moon this weekend will also increase the storm’s tidal impacts, potentially upping the amount of shoreline inundation. There are some model projections that slow or stall Henri as it nears the New England coastline which could prolong coastal impacts into early next week before the storm turns back out to sea.

Other tropical storminess

Meanwhile, the remnants of Fred were drenching central New England with two to three inches of rainfall, prompting flash-flood warnings for the Interstate 84 corridor from northeast of Hartford, Conn., to Worcester, Mass.

Extreme flooding leaves 35 unaccounted for in North Carolina

Fred deluged parts of the Carolina Piedmont with a half-foot of rainfall and dumped more than 10 inches in the lee of the Appalachians. A staggering 17.36 inches was reported in Transylvania County, N.C., where 100 people were rescued and 30 remained missing as of Wednesday night after dire flash-flood emergencies.

Twenty-seven flash flood warnings were issued in the Southeast on Tuesday. There were 13 tornado reports as well.

As if that wasn’t enough tropical activity, Grace is still chugging along, too, and could restrengthen over the Bay of Campeche before striking Mexico again.

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