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Intensifying nor’easter lashing Northeast with flooding rain and high winds

The storm may reach ‘bomb cyclone’ status, with states of emergency declared in New Jersey and New York

European model simulation of storm at 8 p.m. Tuesday. (PivotalWeather)
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A storm offshore of the Mid-Atlantic explosively intensified Monday night, and it is buffeting the Northeast with strong winds and flooding rains as it comes up the coast.

Flash flood watches are up from northern New Jersey and northeastern Pennsylvania into most of southern New England. Up to five inches of rain are possible, falling on soils that are largely saturated following an exceptionally wet summer. Parts of New Jersey have already seen more than 4 inches, with rainfall rates topping an inch per hour.

A state of emergency was declared in New Jersey and New York on Monday due to the anticipated storm hazards. New York City issued a travel advisory through Wednesday morning, advising commuters to allow extra travel time and use mass transit.

“We know how quickly these storms can escalate, so everyone, especially those living in basement apartments, should plan accordingly,” New York Mayor Bill de Blasio (D) tweeted Monday.

Wind advisories also stretch from the nation’s capital to the coastline of Maine, with a high-wind warning up for the shorelines of Massachusetts and Rhode Island, where gusts could top 70 mph. The nor’easter is the first of two sprawling storm systems that will bring inclement weather to the East Coast this week. Its rate of intensification is expected to qualify it as a “bomb cyclone,” or a storm that strengthens with unusual haste.

The storm is the final act of a destructive ensemble that brought tornadoes to the Ozarks and Midwest on Sunday and a line of strong thunderstorms to parts of the Mid-Atlantic overnight Monday, which unloaded one to three inches of rain from Washington to Philadelphia. By Tuesday, rain and downpours were exiting offshore of the Delmarva Peninsula, spiraling into a new developing low-pressure center taking shape off the East Coast.

Nor’easter, currently and the forecast

As of 5 p.m. on Tuesday, the nor’easter was centered just east of New England. Radar showed rain, focused along a stationary front, drenching areas mostly north and west of New York City. Flash flood warnings were in effect for area north of Binghamton through Syracuse and Utica in central New York where 1 to 2 inches of rain had fallen, but was starting to ease some.

Earlier Tuesday morning, downpours prompted flash flood warnings west and south of New York City, which have since expired. Rainfall amounts of one to four-plus inches complicated the morning commute along the Interstate 95 and 84 corridors. Through 1 p.m.., 2.73 inches of rain had fallen in Central Park and 3.08 inches in Newark. The highest totals in northern New Jersey were over 4.5 inches.

During the midday and early afternoon hours up to 2 to 4 inches of rain fell in the Catskills where flash flood warnings were also issued.

Late in the afternoon Tuesday, winds were really starting to crank in the Northeast, as far south as Washington where gusts were frequently topping 40 mph. In eastern New England the strongest winds had yet to arrive but were predicted to ramp up quickly during the evening and overnight.

Through Tuesday evening, the heaviest rain was forecast to lift over eastern Massachusetts, Cape Cod and the surrounding islands, as well as Rhode Island; the Weather Service issued a special bulletin for this zone warning of “excessive rainfall rates combined with increasingly poor drainage.”

Later Tuesday night, rain may expand back south over Long Island and New York City as the storm reverses course toward the coastline. Rain may also redevelop over parts of eastern Pennsylvania and New Jersey for a time Tuesday night before retreating back out to sea toward dawn.

Rain could persist in eastern New England and coastal Maine well into Wednesday before the storm, making a bit of a loop, finally pulls away.

A region primed for flooding

The Northeast is particularly vulnerable to additional heavy rainfall thanks to a waterlogged summer that featured top-tier rain events. The remnants of Hurricanes Ida, Henri and Elsa contributed to nearly 30 inches of rain falling in Boston since June 1, tying for the second-wettest summer on record at Logan International Airport.

New York City saw more than two feet of rain over the summer, followed by a flash flood disaster on Sept. 1, when 7 inches of rain came down in only a few hours’ time. Soil moisture is still running high, meaning parts of the region can’t handle much more water. Relatively dry weather in recent weeks, however, may lower the threat of more serious flooding

Here’s what made the New York City flooding from Ida so devastating

Additionally, rainfall rates from this nor’easter will be considerably lower than when Henri and Ida hit the region and more than three inches fell in an hour. Peak rainfall rates from this event should be about half that.

Strong winds and coastal flooding concerns

Concern is also growing for strong winds near the coastline of New England that could locally top 60 or even 70 mph. While winds will be howling aloft, it’s unclear how much momentum will mix down to the surface. That said, there are reasons to believe this storm may overachieve.

“Typically with these dynamic systems, they tend to overperform most of the statistical guidance,” wrote the National Weather Service in Boston.

The strongest gusts could cause power outages and bring down some trees. The prolonged windy conditions are expected to strip much of the remaining foliage off the trees in New England.

The strong winds and tides running a half foot or more above normal could cause pockets of coastal flooding. Coastal flood advisories are up for much of coastal Massachusetts, Connecticut and Long Island. Relatively low astronomical tides, due to the phase of the moon, will somewhat limit the extent and magnitude of coastal flooding.

Offshore waves of 20 to 25 feet will nevertheless generate pounding surf all along the Northeast coastline, contributing to beach erosion.

A ‘bomb cyclone’ that could evolve into a subtropical storm

The storm is intensifying at breakneck speed, its minimum central pressure likely to drop 24 millibars in 24 hours by late Tuesday. That would qualify it as a meteorological “bomb.” Simulations project its pressure to sink to around 975 millibars, which is typical of Category 2 hurricanes. The presence of anomalously warm Gulf Stream waters, close to 4 degrees milder than average for this time of year, is helping energize the system.

Additional nor’easters and perhaps bomb cyclones are likely in the coming weeks thanks to a strong “baroclinic zone,” or sharp change in air temperature over short distances, made more dramatic by the Gulf Stream.

There’s even a chance that the system could acquire subtropical characteristics thanks to those warm waters and earn a name. The National Hurricane Center estimates a 50-50 shot of that happening. “Wanda” is the final name on the Hurricane Center’s conventional naming list before a supplemental list would be implemented; while the Atlantic Basin looks quiet otherwise, more than a month remains in hurricane season.

Waiting on Wanda: Whether we run out of 2021 Atlantic storm names is a wild card

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