The hottest two days of 2019 are expected Friday and Saturday.
Heat indices are forecast as high as 108 degrees in Niagara and Orleans counties, away from the influence of Lake Erie.
Forecasters at the National Weather Service issued excessive heat warnings from noon Friday to Saturday evening for those counties.
"Heat illnesses are likely for those spending prolonged periods outdoors or in non-air-conditioned locations," the weather service said.
Forecasters said young children and the elderly are most vulnerable to heat-related illnesses.
Warm and muggy conditions are forecast to persist overnight Friday. Temperatures aren't expected to drop out of the 70s, with high humidity.
That will prevent non-air-conditioned buildings from cooling off. The accumulation of heat will persist into at least Saturday.
Elsewhere, heat advisories are posted for the rest of Western New York.
Heat indices in places such as metro Buffalo, as well as the balance of Erie County, Genesee, Wyoming and the Southern Tier counties, could reach 100 degrees during the day Friday and Saturday. The heat index is a measure of temperature in addition to humidity.
High temperatures Friday and Saturday in Buffalo are forecast to be in the upper 80s. High humidity, however, will make it feel much warmer and more oppressive.
"Prolonged exposure or any strenuous activity may lead to heat related illnesses that require immediate medical attention," the weather service said.
Health professionals advise residents to drink ample fluids and avoid outdoor activities.
Cooling centers will be open in several locations.
Checking on home-bound friends and relatives is also encouraged. And under no circumstances should children or pets be left in parked vehicles for any period of time. Temperatures inside vehicles can turn deadly in minutes.
The heat is being generated by a strong ridge of high pressure.
Although it’s not unusual for the summertime in Western New York, the National Weather Service called the set-up a “perfect storm” of variables converging to create dangerous heat.
Besides above-average, low-level temperatures, the air mass also has extraordinarily high humidity and it’s coming at the “thermal solstice,” which means it’s Buffalo’s hottest part of the calendar, climatologically.
This type of heat, at this point in the summer, can be expected once every 10 to 20 years in Buffalo, forecasters said.