The National Weather Service has issued a tornado watch that stays in effect until 10 PM in 16 counties from southeast to northwest New Jersey.

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Other counties in the advisory are Cape May, Atlantic, Camden, Cumberland, Gloucester, Hunterdon, Mercer, Middlesex, Monmouth, Morris, Salem, Somerset, Sussex and Warren.

A watch is essentially an indication that conditions leading to a tornado can develop. A warning is an indication that conditions exist, but haven't fallen into place. An alert means the likelihood of one.

NWS describes typical signs as dark, low-lying and possibly rotating clouds, a dark, almost-greenish sky, large hail and noise resembling a freight train.

Weather officials also recommend having an emergency kit and a family communication plan ready. If the watch evolves into a warning, it's a signal to take shelter immediately.