PHILADELPHIA-AREA residents didn't need a Memorial Day barbecue to feel grilled yesterday.

It was both the heat and the humidity that brought on that first taste of real summer weather on a holiday that marks the unofficial beginning of summer.

It felt more like late July than late May, National Weather Service meteorologist Greg Heavener said yesterday. Yet, we've had early heat waves three years in a row.

"Last year the first heat wave came between June 1 and June 5," Heavener said. "And in 2009, we had a heat wave in April, from April 25 to 27."

The National Weather Service office in Mount Holly, N.J., issued a heat advisory for Trenton, Philadelphia and Wilmington yesterday. The advisory also included New Jersey's Camden, Gloucester and Mercer counties and northern Burlington County as well as New Castle County in Delaware and Montgomery, Chester, Bucks and Delaware counties in Pennsylvania.

Under a heat advisory, a period of hot temperatures combined with high humidity can create situations that lead to heat illnesses, said the weather service.

Folks who gathered yesterday for picnics, parades and other festivities in Bridesburg, Society Hill, Port Richmond and elsewhere broiled on a mostly sunny day with temperatures in the low 90s.

During an excessive heat advisory, people should drink plenty of fluids, stay in air-conditioned places if possible, stay out of the sun, and check up on elderly relatives and neighbors.

Temperatures are expected to be in the low 90s today and tomorrow. There is a chance of showers and thunderstorms tomorrow and tomorrow night.

On Thursday, there is a chance of showers in the morning, but temperatures are expected to cool off with highs in the low 80s.

Heavener said the heat wave this week is only the second time in 25 years that the Philadelphia region had above-average temperatures in April or May following a La Nina winter.

During a La Nina winter, the surface temperatures are cooler than normal around the equatorial Pacific Ocean, he said.

Although drinking fluids is advised during a heat wave, alcohol doesn't count, Heavener said.

"Alcohol does cause dehydration, but we know people are going to drink on a holiday weekend," he added. "Moderation is the best."