Tropical Storm Henri, currently spinning its way west-northwest about 375 miles south, southeast of Cape Hatteras, N.C., is likely to become the first hurricane to make landfall in southern New England in 30 years.

Why it matters: Factors ranging from soggy soils from previous rainstorms to astronomical high tides, and Henri's slow forward motion will combine to create a uniquely dangerous scenario for New England beginning Sunday and lasting through at least Monday.

Driving the news: Tropical Storm Henri has survived a battle with strong upper level winds that have tipped over its towering thunderstorms, putting a lid on its intensification. However, those winds are projected to slacken just as the storm traverses the warm waters of the Gulf Stream in the next few days.

• The National Hurricane Center predicts the storm will become a Category 1 or 2 hurricane within the next 24 hours, before weakening during its approach to New England.

Context: While New England has seen damaging hurricanes before, they are not common. Additionally, when storms get to this high of a latitude, they tend to be moving quickly off to the north-northeast, captured by the jet stream winds aloft.

• Oftentimes, storms in the position where Henri is now tend to curve harmlessly out to sea, but the existence of a high pressure area to the northeast and a low pressure area to the west are projected to funnel Henri up the coast instead.

According to a National Oceanic and Atmospheric Administration (NOAA) database, only five hurricanes have made landfall within 100 miles of Boston since 1950, and the ones on the list are notorious for their damage to coastal areas in particular.

• These include Hurricanes Carol in 1954, Donna in 1960, Gloria in 1985, and the most recent such storm, Hurricane Bob in 1991.
• However, Henri is forecast to be different than every one of these storms, in that it will be moving far more slowly when it nears and crosses the coast. This could lead to rapid weakening once it moves over land, but also prolonged periods of high winds and pounding surf, plus coastal flooding that lasts for more than one high tide cycle.

Threat level: The exact intensity and track forecast for Henri still have considerable uncertainty, with possibilities ranging from a Category 2 storm making landfall in Cape Cod to a strong tropical storm hitting Long Island.

• However, the National Hurricane Center is confident enough to hoist hurricane watches for the south coast of New England, as well as storm surge watches for a maximum surge — the water driven ashore by the storm's winds on top of tide levels of three to five feet — across the same areas.
• What's especially unusual about this storm, though, is that just as Henri nears the coast, atmospheric steering currents are forecast to collapse, causing the storm to slow to a crawl.
• Since Hurricane Bob struck New England in 1991, sea levels have risen due largely to human-caused climate change. This makes any surge more dangerous today than it was during the last hurricane this area faced.

#Henri is expected to slow to a crawl just as it's making landfall in New England. This is exceptionally rare, and has major ramifications with impacts.

The NHC forecast has Henri moving around 5 to 6kts over Rhode Island. The *slowest on record* for a hurricane there is 26kt. pic.twitter.com/R3Kc6pLcPn

— Sam Lillo (@splillo) August 20, 2021

What's next: The Hurricane Center as well as the Boston office of the National Weather Service are urging residents of southern New England as well as New York (particularly from New York City to the tip of Long Island) to prepare for high winds, heavy rains and the potential for prolonged power outages late this weekend and early next week.

• Expect the track and intensity forecast to be fine-tuned Friday and Saturday, and any fluctuations in these expectations will have a major influence on which areas are most likely to see the brunt of the storm.

This is a developing story. Stay tuned for updates.