UPDATE: Serious flooding in Montclair Thursday, with cars trapped.

A tornado warning had been in effect for northeastern Essex County for about a half-hour Thursday evening, ending at 6:30 p.m. While that warning has cleared, the National Weather Service warns an isolated tornado in the area remained possible into the evening.

At 5:59 p.m., a severe thunderstorm capable of producing a tornado was was located over Caldwell, moving northeast at 20 mph, the National Weather Service said. The storm was expected to be near Bloomfield at 6:10 p.m.

A tornado warning is considered more severe and urgent than a tornado watch. While a Watch only indicates tornadoes are possible, a warning indicates a tornado has been sighted or indicated by weather radar.

Under a warning, "There is imminent danger to life and property," the NWS says in its explanation of the terms.

It urges during a tornado warning to move to an interior room on the lowest floor of a sturdy building, and avoid windows. If in a mobile home, a vehicle or outdoors, it says move to the closest substantial shelter and protect yourself from flying debris

While the tornado warning had cleared by 6:30 p.m., a remaining hazardous weather outlook warned "An isolated tornado is not out of the question." That outlook said showers and thunderstorms into the evening may produce damaging winds and heavy rainfall.

Tornado warnings also remained in effect for parts of New Jersey further south. At 6:34 p.m., the NWS said a "confirmed large and extremely dangerous tornado was located over Mercerville-Hamilton Square, or near Trenton, moving southeast at 25 mph."

"You are in a life-threatening situation," the NWS warned the Trenton area. "Flying debris may be deadly to those caught without shelter. Mobile homes will be destroyed. Considerable damage to homes, businesses, and vehicles is likely and complete destruction is possible."

Flash flood warning

The NWS has additionally issued a flash flood warning for the area.

At 6:47 p.m., doppler radar indicated thunderstorms producing heavy rain in Lindurst. Between 1 and 2.5 inches of rain had fallen, and additional rainfall amounts up to 1 inch are possible in area, the NWS said.

Flash flooding was expected to begin shortly in Montclair and several surrounding areas, including Bloomfield, Orange, Caldwell, Fairfield, East Orange, West Orange, Belleville, Livingston, Nutley, Verona, Cedar Grove, West Caldwell, Glen Ridge, North Caldwell and Roseland, the NWS said.

The impact would be on small creeks and streams, urban areas, highways, streets and underpasses as well as other poor drainage and low-lying areas, the NWS said.

— Louis C. Hochman