The National Weather Service says it will feel like 100 degrees in parts of the Philadelphia region as the second heat wave of the year persists for a fourth day.

The steamy conditions in turn have the potential to spawn heavy showers and thunderstorms after 4 p.m. in the city and environs.

The service has issued a heat advisory for the I-95 corridor from Wilmington to Trenton.

While the high temperature for the day is expected to be only about 90, dew points in the 70s will make it feel more like 100 degrees in the afternoon.

“The combination of hot temperatures and high humidity will combine to create a situation in which heat illnesses are possible,” the weather service said. “Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors.”

It also will be hot and humid at the Shore, with an expected high of 87 and a chance of showers and thunderstorms after 1 p.m.

Things will remain unsettled into the weekend, but a cold front will bring some relief Sunday night.

The high temperatures for Saturday and Sunday are expected to be in the upper 80s, so the heat wave that began Tuesday will likely end Friday. But the humidity will linger.

Come Monday, it should be mostly sunny with a high around 86 in Philadelphia and there’s no further precipitation in the forecast until Thursday.