A storm system expected on Saturday could bring New York City and New Jersey an isolated tornado threat, damaging winds and multiple rounds of flooding downpours, with the sharpest danger arriving late in the day.
The National Weather Service said the system could contain wind shear strong enough to spin out a twister, but the greater concern is straight-line wind. NOAA's Storm Prediction Center placed New York City and points west into most of New Jersey under an enhanced risk of severe weather, a level three out of five, signaling a more likely chance of storms that can turn damaging fast.
That risk matters because the storms could pack widespread winds above 60 mph, strong enough to bring down tree limbs and knock out power. The best chance for that kind of weather is late in the afternoon and early in the evening, when people are most likely to be on the move and outdoor plans are hardest to change at the last minute.
The flood threat is broader and lasts longer than the wind threat. Flood watches have already been issued for Saturday in New York City and New Jersey, and torrential downpours may cause serious ponding on roadways while rivers rise. Rainfall rates could reach two inches per hour at times, which can overwhelm drainage quickly even where the strongest wind does not strike.
There is still a built-in split in the forecast. The tornado threat is isolated, not widespread, while damaging straight-line winds are more likely. That means the most common severe-weather problem may not be the one that grabs the most attention, and the areas most exposed to flooding will depend on where the heaviest bands of rain stall during the day and into the night.
The severe weather threat is expected to diminish late Saturday night, leaving Sunday pleasant. Until then, the key window is late Saturday afternoon through the evening, when both the wind and tornado risks are most concentrated and the flooding risk is still building.
