Friday NJ weather: Big cooldown arrives with a bang

The Bottom Line

Friday will be the fourth and final day of New Jersey's latest heat wave. A cold front approaching from the west will fire off some strong thunderstorms in the afternoon and evening hours, which raises flooding alarm bells.

The weekend will start cool, cloudy, and potentially rainy. But it will end with another warmup.

The United States' next big weathermaker is Tropical Storm Ida, eyeing a Gulf Coast landfall Sunday night. The remnants of Ida could drag another round of (heavy) rain toward New Jersey around the middle of next week.

Heat

70s in the morning, 90s in the afternoon. Our heat wave comes to a steamy end Friday.

It will be Newark Airport's 39th 90+ degree day of 2021. That ties this year for 9th, since record-keeping began in 1931. The record is probably out of reach at this point (thankfully) — 54 in 2010.

Far NW NJ may tap into some cooler air on Friday, keeping thermometers out of the 90s. And the Shore will have an early sea breeze, limiting temperatures too. But most of the state will be in the 90-degree neighborhood by about lunchtime.

A Heat Advisory continues for most of the state — generally the NYC metro area, the Philly metro area, and the NJ Turnpike corridor — until 8 p.m. The heat index may hit 100 degrees yet again.

You know the drill. Stay hydrated and stay cool.

Thunderstorms

An approaching cold front will eventually put a definitive end to this stretch of hot, summer days. Of course, as usual, that frontal boundary will cause substantial atmospheric lift. Combined with the heat and humidity in the atmosphere, we are looking at a round of strong to severe thunderstorms.

Best timing for storms on Friday would be from mid-afternoon onward. Storms may pulse down a little bit as they come close to the (cooler, more stable) coast. And they may also lose some "oomph" after sunset. But we do have to keep a chance of storms in the forecast through Friday evening and Friday night too.

Thunderstorms will be scattered, but strong. There could be some wind gusts and wicked lightning in the initial storm cells. But the big concern here will be pockets of heavy rain. Not everyone will see 1 to 2 inches of rainfall — but if you do, and if your soil is saturated, flooding could occur quickly.

A Flash Flood Watch has been issued from 2 p.m. Friday through 2 a.m. Saturday for almost all of New Jersey. (Only exceptions are Sussex, coastal Atlantic, and Cape May counties.)

On that map, you can see a bright green rectangle in North Jersey. That is a continuing Flood Warning for the Passaic River, which is still running above flood stage from Tropical Storm Henri's heavy rainfall last weekend. That water is only going to get higher again if a heavy rain band pours down. So please stay alert and play it safe.

Weekend

For those who wanted a cooldown, you got it for Saturday. Cooler, somewhat drier air and cloud cover will keep temperatures in the 70s all day. That is considerably below normal for late August. An unfortunate way to start the penultimate weekend of the summer season.

In addition, the chance of rain will continue on Saturday, with the previously mentioned front stalled just south of New Jersey. I don't see anything incredibly heavy during the day. But it might be rather "miserable" at times. Best chance of rain will be southern and coastal New Jersey.

Conditions should improve somewhat by late Saturday. And Sunday looks to be the much better day of the weekend. Skies become partly sunny, and temperatures should return to the seasonable 80s. There is a chance of a shower or two on Sunday too, but they look pretty isolated.

Ida

Tropical Storm Ida is in the Caribbean Sea, aiming for western Cuba later Friday. As the storm enters the warm Gulf of Mexico, it is expected to undergo explosive growth. It is forecast to become a major hurricane (111+ mph winds) just before striking the Louisiana coast Sunday night. Not good at all.

We will have to watch closely where the remnants of Ida go after the storm's visit to the Gulf Coast. Models show at least some tropically-enhanced rainfall over New Jersey around the middle of next week — Tuesday night, Wednesday, Thursday. It's way too early for details — the accuracy and precision of tropical storm forecasts are shaky at 72+ hours. But this one is definitely worth watching.

There are two other tropical waves in the Atlantic that are also becoming more organized. The next names on the list are Julian and Kate.

I am technically still on vacation through Labor Day, Monday 9/6. But when potentially nasty weather threatens the Garden State, I can't help but jump in and do a quick write-up. Our entire weather team will continue to keep you updated on the latest forecast through the weekend, next week, and beyond!

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

​​