(CNN) It was close to 90 degrees Friday afternoon when the subway lines in part of New York stopped running and stations became packed with frustrated travelers.

The metro area, home to 20 million people, is one of several major population centers under an excessive heat warning that lasts until Sunday night, making it an especially stressful time to have to find alternative ways home or out to eat.

The subway problems were eventually resolved after a computer problem was fixed, but New York Mayor Bill de Blasio was steamed.

"This kind of meltdown during a heat wave is UNACCEPTABLE," he tweeted. "The (Metropolitan Transportation Authority) owes every single New Yorker an explanation for this. We've known about this dangerous weather for DAYS. There's no excuse for why they aren't prepared."

New York, which declared an emergency because of the heat, is not alone in sweating this weekend out.