As a wave of heat hits New York, the city is opening several hundred cooling stations to mitigate the dangers of heat exhaustion and strokes, officials said.

The National Weather Service is predicting the city will experience heat indexes of more than 100 degrees for the next two days, peaking on Tuesday afternoon.

“That’s our trigger point,” a spokesman for the Office of Emergency Management, Jarrod Bernstein, said. “When we see two days in a row of more than 100-degree heat, that’s when we implement our heat contingency plans.”

The 300 to 400 cooling centers are air-conditioned spaces in community centers and senior citizen homes spread throughout the boroughs. Their locations can be found through the agency’s Web site or by calling 311.

The Office of Emergency Management is monitoring emergency room admissions, ambulance runs, and reports from the medical examiner’s office for heat-related illnesses and deaths, Mr. Bernstein said. Judging from those reports, the cooling centers may be kept open longer. If certain areas of the city have more trouble dealing with the heat, the agency will respond with additional resources, Mr. Bernstein said.

“This is a very serious public health risk,” Mr. Bernstein said.

According to a special heat advisory from the National Weather Service issued for the afternoon hours, a high-pressure system developing in the west is responsible for the “oppressive weather conditions.”

“Temperatures will climb into the mid-90s under hazy sunshine during Monday afternoon,” the advisory said. “Such temperatures when combined with increasing humidity levels, will let the heat index climb to between 100 and 104 degrees during the afternoon hours.”

New York City’s proclivity to humid summer days makes for tough heat conditions, according to the Office of Emergency Management.

Health officials are asking that people wear lightweight clothing, stay hydrated, avoid caffeinated and alcoholic beverages, and check on neighbors, especially the elderly and sick. The Office of Emergency Management’s “Beat the Heat” guide is available on the agency’s Web site and can be requested in the mail through 311.

Spray caps for fire hydrants are available to city residents, but they must be signed out from firehouses by someone who is at least 18 years old. Mr. Bernstein said residents should reduce pressure on electricity companies by running laundry machines and other appliances during the off-peak hours.

Although the heat is expected to be the worst of the summer, a reprieve may not be far off. Late Tuesday, a cold front will likely produce thunderstorms with gusty winds, according to the National Weather Service.