Tri-state residents are being warned to brace for the hottest and longest heat wave of the summer so far.

The temperature hit 90 degrees in Central Park Sunday, marking the start of the steamy stretch. Bridgeport, Islip, Newark and LaGuardia also all had temperature readings in the 90s, and heat advisories have been issued for most of the tri-state for the rest of the week.

Meteorologists say the heat index — what it actually feels like outside — is expected to be at or above 95 degrees. On Monday, the heat index could reach 102 in Central Park.

Isolated thunderstorms are possible for each day of the heat wave ahead, which is expected to break by next weekend, when a cold front makes its way into the area.

New York City’s Office of Emergency Management warned of potential heat illness, advising seniors and people with health conditions to stay in air conditioned areas. The OEM says all New Yorkers should avoid strenuous activity and drink plenty of water.

The OEM says city cooling centers at senior centers, libraries and community centers will be open Sunday through Thursday.

Con Edison says it’s prepared for possible power outages and will have extra crews on call for the duration of the heat wave. The utility company implemented a $1.2 billion upgrade to their power delivery system earlier this year, which should ensure “the undisturbed flow of electricity to consumers,” according to a spokesperson.

During one heat wave stretching from late July to early August in 2006, about 40 people died from heat stroke in New York City, most of them in homes without air conditioning. Health officials later concluded that 100 more deaths during that time were related to the heat.

(AP)