UPDATE : Tornado alerts issued as severe thunderstorms sweep the area

The threat of torrential downpours from the remains of Ida, especially for the northern half of New Jersey, continues to cause concern for meteorologists due to the series of storms that have already saturated the state in recent weeks and Current forecast calling for 4 to 6 inches of rain, with isolated amounts of 8 inches possible by Thursday morning.

Parts of the state could see a month of rain in 24 hours, given that New Jersey typically receives a total of 4 inches of rain in September.

“It’s certainly possible that some parts, like northern Jersey, are seeing more than 4 inches today,” said Nick Carr, a meteorologist with the National Weather Service in Mount Holly. “We don’t mean to be alarmist, but this looks like a big event, especially in terms of river flooding in parts of northern New Jersey.”

Would this be a century-old storm, which statistically means that a storm with so much rain is only expected once a century in a particular area? David Robinson, a New Jersey state climatologist and professor at Rutgers University, says it could happen.

To meet this threshold, totals would need to be around 8 inches or more in places like Newark, New Brunswick, West Milford, Sussex and Flemington.

“Some of the local totals last week reached near or even slightly above the 100-year mark for 12 hours and 24 hours,” Robinson said.

The areas hardest hit during Henry included towns in Middlesex County, where the National Weather Service and CoCoRaHS reported that Cranbury was inundated with 8.91 inches of rain, Jamesburg reported 8.36 inches and Plainsboro received 6.88 inches. In neighboring Mercer County, East Windsor reported 7.94 inches of rain.

Other affected areas in the state include Oakland in Bergen County, which measured 9.22 inches; Ringwood in Passaic County, which received 8.70 inches; Harrison in Hudson County with 8.02 inches; and Lyndhurst in Bergen County with 6.50 inches.

Robinson said normal precipitation for the entire month of September in several New Jersey cities, based on data from 1991 to 2020, amounts to this:

• Sussex: 4.96 inches
• Charlotteburg section of West Milford: 4.88 inches
• Newark: 3.82 inches
• New Brunswick: 4.18 inches
• Flemington: 4.39 inches

“It’s entirely possible that some places will come out of this event after they’ve already passed the 30-year normal for September,” said Robinson.

Flash flood watch is in effect statewide and tornado watch has been issued for 15 of the state’s 21 counties.

What is of most concern to the Weather Service is the amount of rain that has already fallen from two other storms over the past three weeks – the remnants of Tropical Storm Fred, which has soaked Pennsylvania and parts of the New Jersey, and Tropical Storm Henri, which dropped 9 inches or more of rain in some areas.

“Three in quick succession is obviously not great,” Carr said. “The soil is quite saturated, cannot absorb much more – all of this contributes.”

“We would have problems with that amount of rain no matter what, but in this case it’s even worse,” he said.

Robinson said more than 6 inches of rain over a good portion of a drainage basin (small or large) will likely cause flood levels to be exceeded.

“The ground is pretty wet before this event and rivers are flowing about twice as much as they were several weeks ago,” said Robinson. “Notice, at their peak about 10 days ago, they were sinking up to 1,000 times where they were, so they’ve gone down dramatically. “

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Anthony G. Attrino can be reached at tattrino@njadvancemedia.com.