A Northeast heat wave sent temperatures soaring into the summerlike 90s, tying or breaking all-time May records in a few places, including Philadelphia.

This was a four-day heat wave that stretched from May 17-20 with over 70 daily record highs tied or set in the East from Georgia to Maine. Some of the high temperatures during the hottest three days of the heat wave are plotted on the map above.

(MORE: Heat Wave Impacts)

May Monthly Records

Three cities who either tied or set new records for the entire month of May.

Philadelphia soared to 98 degrees on May 19, topping their previous all-time May record of 97 degrees set from May 30-31, 1991. That's also 11 days earlier than that previous May record in Philly and either as hot or hotter than their hottest temperature recorded in 11 of the past 13 years since 2013.

Newark, New Jersey (99) and Reading, Pennsylvania (97) also tied their May monthly record highs on May 19.

Boston (96) had their hottest May day since May 31, 1944, just one degree off their all-time May record from 1880. The following day, Atlantic City (97) had its hottest May day since 1969, just 2 degrees shy of their all-time May record.

While not monthly records, Erie, Pennsylvania (90), and Syracuse, New York (91), had their first high in the 90s of the year, just four days after shivering with a high of only 51 just four days earlier.

Daily record highs highs were set as far north as Bangor, Maine (89 and 87 degrees on May 19 and 20). Portland, Maine, soared to 92 degrees on May 19, about a month earlier than they typically see their first 90s of the year.

(MORE: 5 Things To Know About Staying Safe In A Heat Wave)

Why So Hot?

A zone of sinking air moving eastward at a turtle's pace began in the West and was responsible for record warmth from coast-to-coast. This temporary bubble of high pressure set up near the East Coast, and coupled with warm southwesterly winds, sent temperatures soaring in much of the East.

Fortunately it was only modestly humid in the Northeast, with dew points only as high as the 60s expected, rather than the oppressive 70s often found in summer.

(MORE: What Does The Dew Point Mean?)

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.