Temps could be as high as 90 degrees with high humidity, which will help fuel the storms, expected to begin sometime in the late afternoon, forecasters from the National Weather Service and Accuweather say.
The clustered storms could start around 4:30 p.m. in Central PA and hit North Jersey around 8:30 p.m.
While not all areas are expected to get storms, the ones that do hit could be damaging with gusty winds, lightning and hail possible.
"One noticeable difference, in addition to the heat, will be significantly higher humidity levels on Wednesday, compared to this past weekend," AccuWeather Meteorologist Matt Benz said.
Temperatures could feel 5 to 15 degrees higher than they actually are during the midday hours because of the humidity.
AccuWeather forecasters urged people to limit physical exertion and stay hydrated if they are spending time outdoors.
Rain and storms should clear up overnight with Thursday shaping up to be the nicest day of the week. Temps are expected to be in the low 80s and skies are sunny.
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