Two storm systems are expected to merge into one strong coastal storm in the northern Atlantic overnight Monday into Tuesday morning, bringing periods of heavy rain, gusty winds and flash flooding threats to the New Jersey region.
Forecasters say the coastal storm will likely be classified as a nor’easter — a type of storm more common in the winter than autumn — because the winds are expected to be blowing from the northeast.
AccuWeather says the storm has the potential to strengthen into a “bomb cyclone” as it moves away from New Jersey’s coastal waters and heads up to eastern New England. A bomb cyclone is a storm that rapidly intensifies, with its atmospheric pressure dropping at least 24 millibars during a 24-hour period.
When will the storm hit N.J.?
As of Monday evening, there are two different low pressure systems spinning in different regions of the country — one near the coast of North Carolina and one in the Ohio Valley. Forecasters are expecting the two systems to merge into one by early Tuesday morning as it moves a couple of hundred miles off the coast of southern New Jersey.
The storm will then move north and east towards Long Island, eastern Connecticut and eastern Massachusetts as it strengthens.
When will the rain start?
Some rain showers are expected to arrive in New Jersey around 7 or 8 p.m. Monday, but the heaviest and steadiest rain will likely fall late Monday night through Tuesday afternoon. Depending on the track of the storm and how long it continues to spin counter-clockwise out in the Atlantic, lingering showers could continue into Tuesday night and early Wednesday morning.
How much rain will we get?
The National Weather Service says 3 to 4 inches of rain is expected to fall in many areas of New Jersey from Monday night through late Tuesday, and some areas could get as much as 4 to 6 inches of rain by the time it tapers off.
If rainfall totals do get as high as 4 inches, that would be a month’s worth of rain in less than two days.
Forecasters from NBC4 in New York are predicting as much as 4 to 5 inches of rain over a large swath of New Jersey, New York City and Long Island, New York, and AccuWeather is predicting as much as 4 to 8 inches of rain in parts of Connecticut, Massachusetts and Rhode Island.
Is flash flooding a concern?
Because the rain could fall at a rate of 1 to 2 inches per hour at times, the weather service says there’s a threat of flash flooding Monday night through late Tuesday afternoon. The most vulnerable places for flooding will be streams, creeks, city streets and highways, especially those in low-lying areas and those with bad drainage systems.
A flash flood watch, which is not as urgent as a warning, goes into effect at 8 p.m. Monday and runs through 5 p.m. Tuesday. The watch originally covered 17 of New Jersey’s 21 counties, but it was expanded Monday afternoon to include Camden County.
So now, every county in the state is under a flash flood watch, except for Cumberland, Gloucester and Salem.
Is New Jersey under a state of emergency?
Late Monday afternoon, Gov. Phil Murphy declared a state of emergency for New Jersey ahead of the nor’easter, because of the predictions of heavy rain, flash flooding and strong winds.
The state of emergency goes into effect at 8 p.m. Monday, officials said.
Is there a thunderstorm threat?
The Storm Prediction Center, affiliated with the National Weather Service, says there’s a marginal risk of severe thunderstorms in New Jersey Monday afternoon and Monday night. That’s the lowest of five threat levels for severe weather.
UPDATE (6:40 p.m. Monday): Some rain showers and thunderstorms have moved into southwestern New Jersey, and the weather service has issued a severe thunderstorm warning for one area — the northwestern region of Salem County. The warning is effective until 7:15 p.m., with the possibility of 60 mph wind gusts and small hail.
UPDATE (7:05 p.m. Monday): The National Weather Service said an area of strong thunderstorms will impact parts of northwestern Atlantic, Cumberland, Salem, Camden and Gloucester counties, along with northwestern Atlantic County and west-central Burlington County now through 7:45 p.m. Although the storms are strong, with wind gusts up to 45 mph, they have not reached severe status, which is why a severe thunderstorm warning has not been issued for these areas.
Is there a tornado threat?
Forecasters initially said an isolated tornado is possible when the storm hits New Jersey, but the latest forecast from the Storm Prediction Center shows no tornado threat for the Garden State. The agency says there’s a 2% to 5% chance of a tornado forming in other states, including Virginia, West Virginia, Ohio and North Carolina. (see map below)
Is coastal flooding a concern?
Forecasters say minor coastal flooding and flooding of low-lying roads, is possible along the Jersey Shore and Delaware Bay, especially during high tide cycles Tuesday and Wednesday.
A coastal flood advisory issued by the National Weather Service says minor flooding could occur in Hudson County, eastern Essex County and eastern Union County. The advisory went into effect shortly after 5 p.m. Monday and is active until 3 p.m. Tuesday.
How strong will the winds get?
The weather service is predicting wind gusts as high as 45 mph overnight Monday and during the day on Tuesday, mainly along the Jersey Shore. Winds can also gust to 60 mph or higher if severe thunderstorms develop. In either case, forecasters say there will be a risk for scattered power outages.
Could the nor’easter fizzle out?
Forecasters from the National Weather Service say there’s a possibility the center of the coastal storm will develop and strengthen farther offshore than some computer guidance models had originally projected. As a result, that could push the heaviest rain and strongest winds more offshore and lessen the impacts on interior sections of New Jersey.
However, the weather service said these types of offshore storms have a “notoriously high uncertainty pattern,” so they still believe this storm “has the potential to be high impact for our region.”
Even though there’s still some uncertainty over where the coastal storm will develop, heavy rain and strong winds are likely, especially near the Jersey Shore, said Dean Iovino, a meteorologist at the weather service’s regional forecast office in Mount Holly.
“I would not let my guard down if I lived in New Jersey,” he said.
Are we getting another nor’easter this week?
Forecasters say another storm system could move into the New Jersey region later this week, bringing the potential for moderate to heavy rain. But they don’t yet know if it will be classified as a nor’easter.
As of now, the National Weather Service’s Mount Holly office is calling it “another strong surface low” and says it will likely drift from the southern Plains Wednesday night up to the Northeast region by the end of the week.
The weather service’s New York regional office says New York City and northern New Jersey could be in for “a prolonged wet period from late Thursday night into early Sunday as the surface low track across the Mid-Atlantic region and then the northeastern states.”
Current weather radar
p class=”article__paragraph article__paragraph–left” id=”7Q2KYPGQBFDZRPJV2OARCT2N5M”>Thank you for relying on us to provide the local weather news you can trust. Please consider supporting NJ.com with a voluntary subscription.
Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com.