Sweltering temperatures that are challenging records across the nation and contributed to several deaths have triggered heat advisories and warnings Wednesday in Philadelphia, Washington and the mid-Atlantic region.

The National Weather Service is predicting a heat wave with temperatures nearing 100 degrees. Forecasters said it will feel even hotter with high humidity and a ridge of high pressure parked over the East Coast and Southeast states through Thursday.

“We’re forecasting the high to be pretty close to the record” of 98 degrees set for Washington in 1999, said Brandon Peloquin, a meteorologist with the National Weather Service. The normal high temperature this time of year in the nation’s capital is about 82 degrees.

“As you can see that’s quite a bit higher than normal this time of year,” Peloquin said. “I’m not sure it really says much about what the summer is going to be like.”

Still, the official arrival of summer is still about two weeks away.

High temperatures contributed to the deaths of four elderly people in Maryland and Tennessee in recent days.

The National Weather Service issued a heat advisory for the Baltimore-Washington region and a higher-level excessive heat warning for Philadelphia, where similar temperatures are forecast. Heat advisories also were issued for parts of Ohio, Indiana and Michigan.

Air quality alerts also were issued across the region, including in New Jersey. Officials said ozone levels could cause problems for children, the elderly and those with respiratory problems. The state’s Health Department said men ages 65 to 84 years of age are the largest group hospitalized for heat exposure each year.

Public schools in Philadelphia and parts of New Jersey cut their school days short in response to rising temperatures.

In the District of Columbia, trash collection will begin an hour earlier than normal because of the extremely hot weather forecast. City officials warned residents not to open fire hydrants to cool off because it reduces water pressure and hampers firefighting.

As the heat wave has pushed east, it has crushed previous record highs in St. Louis and St. Paul, Minn., where the mercury reached 102 degrees on Tuesday and finally melted a giant snow pile in a Sear’s store parking lot.