Debby is a downpour and tornado machine: Stormy day for NJ Friday

UPDATE as of 2:15 p.m. Friday...

The original Tornado Watch from this morning was allowed to expire at 2 p.m. A new watch was issued for 11 counties in northern and central New Jersey until 10 p.m. Friday.

ORIGINAL POST from 7:29 a.m. Friday...

Storm Info / Track

Welcome to Debby Day. This is going to be an active weather day for New Jersey, with multiple hazards developing through the afternoon and evening hours.

Since Debby made landfall as a category one hurricane in northwestern Florida, its reach has been wide-reaching. Up to 18 inches of rain was reported in Florida, according to the Applied Climate Information System. And there have been 55 tornado reports nationwide since Sunday, according to the Storm Prediction Center. That is why I have no problem calling it a "downpour and tornado machine" — especially since those are New Jersey's two big threats Friday.

As of 5 a.m. Friday, Post-Tropical Cyclone Debby was centered over West Virginia. It will continue charging north, making its closest pass to New Jersey later Friday, just to our west.

There are still two big concerns as Debby's "brunt" kicks in Friday afternoon and evening: Flooding downpours and tornadoes.

Some wind, rough surf, and minor coastal flooding are possible too.

Get our free mobile app

Forecast Changes

I have made a few minor tweaks to Friday's forecast, based on current trends and the latest model data. That includes:

1.) An earlier arrival time for the brunt of the storm, by a couple hours. The heaviest rain and thunderstorm chance will kick-in in the middle of the afternoon, lasting through at least early evening.

2.) An overall higher risk of tornadoes.

3.) Stronger winds. Gusts could reach 40 mph (inland) to 50 mph (coast).

4.) A slightly higher risk of coastal flooding, although still only in the minor category.

Timeline

First of all, it is very humid outside. Downright tropical. Temperatures are mainly in the 70s, with highs reaching the lower 80s Friday afternoon. That warmth and humidity will help to fuel the strong storms and heavy rain coming up later today.

We have seen spotty showers and downpours around so far Friday morning, which will generally be the forecast through midday. Having said that, it looks like we will catch a general lull in rainfall through about lunchtime.

Skies will be mostly cloudy to overcast. (I would be very concerned if we catch substantial breaks of sun at some point, cooking the atmosphere and dramatically raising our severe weather threat level.)

The "brunt" of Debby — the big "grand finale" push of pouring rain and strong thunderstorms — will start around 2 or 3 p.m. The flooding and severe weather will carry on through the evening hours, probably until about 9 or 10 p.m.

By around Midnight, I think rain will exit the Garden State and the wind will calm down. Skies will clear through the rest of the overnight. Low temperatures will dip to around 70 degrees.

Impacts

Typical of tropical cyclones, Debby will be a multi-impact, multi-hazard event. By the numbers, here are the things to watch for, in descending order of concern:

1.) Heavy Rain / Flooding... An additional inch or two of rainfall is expected from Friday through Friday night. (A little less close to the coast.) The ground is saturated from rain and downpours over the past three days. In some spots, only a half-inch of rain in one hour (or one inch in six hours) would be enough to overwhelm storm drains and small creeks. So we are not talking about "biblical" rainfall here. It's just that it won't take much to snarl traffic and possibly cause property damage.

2.) Severe Weather / Tornadoes... Our atmosphere feels tropical, rife with humidity. Add in plenty of instability and wind shear, as Debby's center approaches, and you get an elevated risk of dangerous, twisting storms. In particular, a couple quick spin-up tornadoes are possible at some point Friday. Damaging straight-line winds or downbursts are a possibility too. Best chance would be from mid-afternoon on, along the western edge of the state.

3.) Wind... Friday is going to be a windy day, especially once thunderstorms are in the neighborhood. Top gusts around inland New Jersey are expected to peak around 40 mph. Near the coast, the southeasterly wind will be stronger, up to about 50 mph. That is strong enough to blow down trees and power lines, and make driving difficult at times too.

4.) Rough Surf / Coastal Flooding... A high risk of rip currents is posted for the Jersey Shore once again Friday, with 3 to 6 foot ocean waves forecast. In addition, there will be just enough of an on-shore push of ocean water (storm surge) to spark alarm bells for minor coastal flooding. That basically equates to "the usual spots," which tend to flood anytime there is a big storm around. The most vulnerable spots for elevated tidal waters will be Ocean County and up the Delaware River basin.

Advisories

A Tornado Watch is in effect for 17 of New Jersey's 21 counties until 2 p.m. Friday. That serves as a formal heads-up that the ingredients are present for severe weather, including possible tornadoes. (I fully expect that watch to be re-upped/expanded/extended much later than the afternoon.)

Counties under the Tornado Watch include: Atlantic, Burlington, Camden, Cape May, Cumberland, Essex, Gloucester, Hunterdon, Mercer, Middlsex, Morris, Passaic, Salem, Somerset, Sussex, Union, and Warren. (Basically everything except the northeastern edge of the state: Bergen, Hudson, Monmouth, and Ocean)

In addition, a Flood Watch covers the following 11 NJ counties until 1 a.m. Saturday:
Northwestern Burlington, Camden, Gloucester, Hunderston, Mercer, Middlesex, Morris, Salem, Somerset, Sussex, and Warren. That area has the highest risk of both pre-saturated soils and heavy downpours on Friday.

A Wind Advisory cautions of wind-driven power outages, damage, and driving difficulties due to 40-50 mph gusts. The advisory is in effect:
—Now until 8 p.m. for Northwestern Burlington, Camden, Gloucester, Hunderton, Mercer, Middlsex, Morris, and Somerset counties.
—From 11 a.m. until 8 p.m. for Sussex and Warren counties.
—Now until 11 p.m. for Atlantic, Southeastern Burlington, Cape May, Cumberland, Monmouth, Ocean, and Salem counties.
—From Noon until 11 p.m. for Hudson county.

And a Coastal Flood Advisory has been issued for a few shore points subject to about a foot of tidal water rise. Advisories are posted:
—Until 6 a.m. Saturday for Ocean county.
—From 1 p.m. to 5 p.m. Friday for Salem county.
—From 4 p.m. to 10 p.m. Friday for Northwestern Burlington, Camden, and Gloucester counties.

Weekend Forecast

By the time you wake up Saturday morning, Debby will be but a distant memory. Beautiful weather takes over for the weekend.

Saturday will become mostly sunny, with lower humidity levels. (I don't want to call it "low" humidity just yet, as dew points may still be in the sticky 60s for part/most of the day.)

It will be a dry weather day, with an occasional breeze. And definitely warm, with high temperatures in the lower to mid 80s.

Sunday also looks pleasant, with partly sunny skies and lower 80s.

Most of next week will also feature great weather. Comfortable 60s in the morning. Warm lower 80s in the afternoon. With low humidity and general mixes of sun and clouds. I can't rule out a few sprinkles and showers along the way, but the vast majority of New Jersey will stay dry.

Next opportunity for a more widespread storm system now appears to be at the end of next week. We will also have to watch the tropical Atlantic closely for our next development there, as we approach the climatological peak of hurricane season.

Be smart and stay safe out there.

Dan Zarrow is Chief Meteorologist for Townsquare Media New Jersey. Follow him on Facebook for the latest forecast and realtime weather updates.