Severe storms descended on the Philadelphia region Thursday, bringing with them a flash flood threat, damaging winds, and the possibility of isolated tornadoes. Forecasters warned that the evening commute could be a mess as heavy downpours were expected to saturate roads and cause travel disruptions.
The threat level has escalated in parts of New Jersey. The National Weather Service’s Mount Holly forecast office elevated a wide swath of northern and central New Jersey from a “slight” risk to a “moderate” risk of excessive rainfall. Moderate is the second highest of four threat levels.
“This means that instances of flash flooding could be fairly widespread and potentially significant within this area,” the weather service said in an update Thursday afternoon. The moderate risk zone includes the Philadelphia metro region and extends northeastward into portions of central and northern New Jersey.
Warm temperatures and high humidity were expected to energize thunderstorms developing along a cold front, causing some storm cells to intensify. The strongest cells could dump rain at a very high rate, with some areas of the Garden State potentially getting 3 to 5 inches by Thursday night.
“Travel disruptions are increasingly likely for the evening commute as some roads may flood later today,” the agency noted.
A flood watch has been expanded to include 18 counties, effective from noon Thursday to 2 a.m. Friday. The watch stretches from Philadelphia to New York City, according to ABC News.
Adding to the danger, wind shear in the atmosphere could spawn tornadoes, especially in the southern half of New Jersey. The Storm Prediction Center put the chance of a twister touching down within 25 miles of any location at 5% to 9%. While that may not sound like a high probability, it’s fairly rare in New Jersey.
Forecasters said any tornadoes that form could be as strong as EF-2 on the Enhanced Fujita scale, packing top winds of 111 mph to 135 mph. The state also faces a moderate risk of severe wind damage from strong thunderstorms or tornadoes, meaning downed trees, snapped electrical lines, and scattered power outages are on the table.
The timing of the storms has been tricky. Initially expected to pop up in the early afternoon, the timeframe was delayed. The Storm Prediction Center said thunderstorms are likely to develop and intensify through 4 to 6 p.m., accompanied by the risk of a couple of tornadoes initially and increasing potential for strong to severe gusts spreading toward coastal areas into early evening.
For the broader Mid-Atlantic, the threat extends from Virginia up to Connecticut. Along the Interstate 95 corridor, heavy thunderstorms could bring damaging wind gusts, rainfall rates reaching 2.5 inches per hour, and total rain accumulation of 3 to 5 inches. The heaviest storms may begin around 3 p.m. in Philadelphia and Baltimore, then reach New York City around 5 p.m., though forecasters say the exact timing is uncertain.
Air travel could be affected as well. Officials at John F. Kennedy Airport warned Thursday that the weather might cause flight disruptions.
