Nor’easter to lash New England with heavy, wind-swept rains

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A powerful fall nor’easter is set to pound New England Wednesday night, unleashing heavy rain and possibly damaging winds. It’s a setup reminiscent of scores of whopper Northeast snowstorms, but this system will be wet, and not white.

The powerful cyclone will organize rapidly Wednesday, qualifying as a meteorological “bomb,” due to its speed as it strengthens. The stage is set for a potentially impactful Wednesday night across the Mid-Atlantic and Northeast.

The storm will start to gather itself to the south of New England on Wednesday morning. The National Weather Service in Boston noted that “altogether, this storm looks progressive,” moving quickly enough that widespread freshwater flooding from rainfall shouldn’t be an issue, though there may be isolated instances of urban flooding. With low astronomical tides, coastal flooding is unlikely to be a concern.

The biggest impact will be the wind. Winds will start to pick up from the south early Wednesday afternoon, beginning to gather steam east of the Interstate 95 corridor a couple hours after lunchtime. Gusts of 30 mph to 40 mph will be the story from the Carolinas up through the Delmarva Peninsula, with 40 mph to 45 mph gusts around dinnertime along the Jersey Shore and shortly thereafter in the New YOrk. Winds will start howling over Long Island a bit after sunset, with gusts to 55 mph possible.

It’s important to note that there are still uncertainties with timing; if the storm comes in faster, it could affect areas farther north during the evening commute, such as the Boston to Providence, Rhode Island, corridor.

That stretch of southern New England will see the greatest impacts. Sustained southerly winds of 30-mph to 40 mph with gusts to 60 mph are possible inside Interstate 495, with slightly lesser amounts to the west. The exception will be in the Worcester Hills and the Berkshires, where sporadic gusts topping 45 mph are possible.

Along the coastline, gusts of 60 mph are possible, except the Cape and Islands, which may see 65 mph wind gusts for a five- or six-hour window around midnight Wednesday night. Again, that timing is flexible, as is the exact track. Onshore easterly winds could cause some coastal erosion.

There is a slight risk that a narrow channel of winds in excess of 80 mph, exceeding hurricane force, could develop and target the Cape. That threat appears low right now, but is growing.

Strong easterly winds will ride up the coastline, affecting Cape Anne, the New Hampshire Sea Coast, before winding down some as the system sideswipes Maine en route to the Canadian Maritimes.

Heavy rainfall will also accompany the gale, sparking overnight urban flood concerns. One to 2 inches are possible near and east of Interstate 84, with local amounts surpassing 2.5 inches in eastern and southeastern Massachusetts. Downeast Maine is a secondary spot that may pick up close to 1.5 inches to 2 inches. In between, amounts around an inch will paint the map.

If the storm takes a more direct path inland, some 3-inch amounts or greater are possible.

“Within a 6 to 12 window, we’ll see that potential for damaging winds with fully leafed trees,” said Hayden Frank, a meteorologist at the National Weather Service in Boston. The full foliage will make it easier for trees to suffer wind damage, bringing down power lines in spots.

A shot of cooler Canadian air will follow the departing system to usher in the weekend.

The nascent storm is a classic “Miller B” setup, a recipe involving a shot of moisture from the south and a zone of low pressure over the Midwest.

The moisture that will feed the storm is streaming north from the Gulf of Mexico, pooling along the Interstate 10 corridor down south to spark heavy rainfall concerns Monday and Tuesday. A surface low will form with that clustered rain activity Tuesday, likely near the southern Appalachians.

Around the same time, a dip in the jet stream and associated cold pocket will lunge southward over the Great Lakes late Tuesday night, translating eastward throughout the day Wednesday. Rising motion ahead of this jet stream “trough” will help intensify the surface low, which by then should be exiting the coastal Carolinas, where heavy rainfall is possible. The strong dip in the jet stream will also yank this system northward, where it’s poised to become a major New England nor’easter by Wednesday night.

The cyclone will undergo “bombogenesis,” meaning its central pressure will drop by at least 24 millibars within 24 hours. The lower the pressure the stronger the storm.

The biggest outstanding wrinkle in the storm forecast is its track. The American model passes a weaker system offshore of Cape Cod, while the European takes a stronger storm inland in southeastern Massachusetts. The coming days will require additional fine tuning to sort out that uncertainty, which will have large bearings on where the heaviest rain and strongest winds occur.