A tornado watch means conditions are favorable for tornadoes to develop during severe thunderstorms.
UPDATE: Storms leave thousands of homes without power
The National Weather Service has issued a tornado watch for five counties in the northeastern region of New Jersey, effective now through 10 p.m. Friday, and a severe thunderstorm watch for the entire Garden State.
A tornado watch -- posted for Bergen, Essex, Hudson, Passaic and Union, as well as New York City -- means conditions are favorable for the development of funnel clouds during severe thunderstorms. If any funnel clouds are spotted on radar or in the sky, the watch will be upgraded to a warning.
At 4:40, a flash flood warning was issued for central Monmouth County. The flooding could affect travel on the Garden State Parkway, according to the NWS. The warning will expire at 8:30.
A flash flood warning was also issued for Cumberland County until 8:45.
The tornado watch was issued at about 1:30 p.m. Friday, ahead of stormy weather that is expected to sweep across the Garden State later in the afternoon and evening as a strong cold front moves in from the west.
Early Friday morning, the weather service said there was a "small chance of isolated tornadoes, mainly from the New York City metro area on west and north," but no formal watches were posted until the early afternoon.
Also in the afternoon, the national Storm Prediction Center upgraded the risk of severe thunderstorms for the northern half of New Jersey -- from Trenton, along the I-95 corridor and up to High Point -- from "slight" to "enhanced."
That means it is more likely severe thunderstorms will develop Friday afternoon and evening in those regions of the state, but there's still a slight risk of nasty weather in southern New Jersey and along the Shore.
As of 2:05 p.m., a strong thunderstorm cell was moving into parts of Mercer County and was heading toward southern Middlesex County and north-central Burlington County, the National Weather Service said.
@GarySzatkowski Hainesport where I am right now pic.twitter.com/4mHjr5CQHP
-- NJ Weather Blogs (@NJWeatherBlogs) July 1, 2016
Decent size hail that fell in Hainesport #NJ. @NWS_MountHolly pic.twitter.com/MmXLrQ9EaO
-- NJ Weather Blogs (@NJWeatherBlogs) July 1, 2016
The storms that develop late Friday are expected to move out of the region by 3 a.m. Saturday, setting up a stretch of dry weather for the holiday weekend.
Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com. Follow him on Twitter @LensReality. Find NJ.com on Facebook.