Tropical Storm Henri, currently located about 490 miles southeast of Cape Hatteras, North Carolina, is forecast to intensify into a hurricane Friday and may pass close to or make landfall in southern New England late this weekend.
Why it matters: A slow-moving Category 1 hurricane or strong tropical storm spinning near Cape Cod could pound the region with high surf and coastal flooding in particular, which could be heightened by rising sea levels from long-term climate change.
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Driving the news: Tropical Storm Henri may be moving slowly to the west-southwest now, but forecasters anticipate it will get pulled north, toward New England, by the weekend. If it makes landfall in southern New England as a hurricane, it would be the first hurricane to make landfall at such an intensity (Category 1 or greater) since Hurricane Bob in 1991.
Details: Tropical storms and hurricanes are extremely powerful weather systems, but they don't drive themselves. Instead, they are steered by atmospheric features around them, such as cold fronts and low-pressure areas.
In this case, a strong area of high pressure is located to the north-northeast of Henri, and the circulation around this high is pushing the storm to the west-southwest.
By Friday and Saturday, however, the storm — by then forecast as a Category 1 hurricane — is expected to make a sharp turn to the north as a cold front digs southeastward toward the East Coast, instigating winds blowing from south to north over the warm waters of the Gulf Stream.
Depending on the timing of this turn, and a subsequent pivot to the northeast, Henri could make landfall somewhere in southern New England or skirt the coastline.
Combined computer model projections from the European and American models for Tropical Storm Henri. Graphic: Tomer Burg
Threat level: In either scenario, significant impacts in the form of heavy rain, strong winds and coastal flooding look increasingly likely, particularly on Long Island, Martha's Vineyard and Nantucket as well as Cape Cod. However, given a high degree of uncertainty in the track forecast, it's possible that Providence and Boston could also be affected.
The timing on these threats is Sunday through Monday, as the storm slowly spins its way northeast, back out to sea.
The National Hurricane Center plans to issue tropical storm and/or hurricane watches for southern New England on Friday.
"The risks of storm surge, wind, and rain impacts in portions of southern New England and eastern Long Island are increasing," the Hurricane Center wrote in a forecast discussion posted to its website Thursday morning.
"Right now, it is advisable to begin preparing for a possible landfalling storm in [southern New England] — a good reference is ready.gov/hurricanes. Onset of tropical storm force winds is most likely first thing Sunday morning, so that is when preparations need to be complete. Having extra cash on hand, gas in vehicles and nonperishable food are recommended if power is lost for a time," the Weather Service forecast office in Boston stated.
Yes, but: Henri is currently battling wind shear, which occurs when winds blow in different directions and/or at different speeds with height, and this is impeding intensification on Thursday.
The shear is expected to diminish Friday, but intensity forecasts have a higher amount of uncertainty compared to storm track projections. The intensity of the storm will play a role in determining its path, with a weaker tropical storm more likely to track further to the east, away from land.
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