As New Yorkers prepare to deal with record temps on Sunday — again — Mayor Bill de Blasio urged residents to take the weekend heatwave seriously.

“This is really serious. This is not business as usual,” the mayor said on Good Morning America Sunday morning.

Those who stay in the city Saturday roasted with the heat matching a 2011 record high — 96 degrees at Kennedy airport — and Sunday’s forecast called for the mercury to reach even higher.

Meteorologists are calling for a high of 99 Sunday, with a severely uncomfortable heat index as high as 107. The National Weather Service has issued an excessive heat warning until 9 p.m., suggesting people to stay indoors with air conditioning.

“The weather service called this one almost to the exact degree,” de Blasio said.