A dangerous heat wave is underway in Philadelphia. It could be the city's worst in 15 years.

A dangerous heat wave is underway in Philadelphia and the surrounding suburbs this week, just as the long holiday weekend is set to draw people outside for Fourth of July celebrations.

A NEXT Weather Alert is in effect through Sunday. Temperatures each day could surpass 100 degrees, and with the humidity, it could feel closer to 105-110.

This is likely the worst heat wave the region has seen since 2011, and we're chasing potentially all-time record high temperatures in Philadelphia.

This is part of a heat wave covering half the nation that will shatter heat records from the Rockies to the East Coast.

An extreme heat warning is in effect in much of the Philadelphia area. Kent, Cape May, Atlantic and Cumberland counties are under an extreme heat watch, according to the National Weather Service.

Heat health emergency in Philadelphia

Philadelphia is under a heat health emergency from 11 a.m. Wednesday through 8 p.m. Sunday, the city announced.

The PCA Heatline (215-765-9040) will be available between 8:30 a.m. and 8:30 p.m. during the emergency, according to the city. City health department nurses will be available to speak with callers about medical problems related to the heat.

This map on the city of Philadelphia's website shows cooling center locations, which will be open during the emergency. Residents are also encouraged to visit any of the over 150 Philadelphia Parks & Recreation's spraygrounds and pools.

The city's older adult centers all have air conditioning and are open between 4 p.m. and 7 p.m., Monday through Friday, and 12 p.m. and 5 p.m. on weekends.

Philadelphia Water Department shutoffs are suspended during a the health emergency. Shutoffs for non-payment will resume after the emergency ends.

If you see someone experiencing homelessness who needs help, you can call the city's homeless street outreach hotline 24/7 at 215-232-1984.

What could be impacted by the heat?

All outdoor plans could be impacted by the heat, including America 250 events, the World Cup match on Saturday at Philadelphia Stadium, and the FIFA Fan Festival at Lemon Hill.

The extreme heat could also impact air travel in Philadelphia and cause roads and railways to buckle.

Cars will quickly overheat, and power outages and rolling brownouts are possible.

The heat will hit the elderly, children, people with chronic illnesses, outdoor workers and pets the hardest. The cumulative effect of consecutive hot days and nights is also likely to lead to increased health emergencies. 

Urban heat island effect

All big cities, including Philadelphia, absorb heat and retain it for days. This makes it hotter during the day and reradiates heat at night, which keeps temps hotter.

The highest humidity during this heat wave will be at night and in the morning. That is why hot and humid nighttime conditions make a heat wave even worse.

After thousands died in the great 1995 heat wave, including more than 700 people in Chicago, large cities have implemented more cooling centers, hotlines, wellness checks, etc.

Many deaths are due to heat stroke from outdoor activities and people who have to stay home and have no AC, especially in rowhomes that retain so much heat. Pets are also in danger during these extreme temperatures and need shade and cool water.

Zoos have special protocols for the animals during extreme heat.

How to prepare for the heat

Before the heat wave takes full effect, be sure you have somewhere cool to rest, organize special care for pets, check on neighbors and family, limit time outdoors, check fluid in cars and stay hydrated.

Swimming pools, movie theaters and shopping malls are places you can stay cool.

Cars become death traps in the heat. No people or pets should ever be left in the car. The heat can reach 125 degrees in minutes and cause death, so always check your back seat before leaving a car.

Buildings with no AC will heat up and retain the heat. That cumulative effect of the heat after 3-5 days could be deadly for some.

Philly-area heat records since 1984

• There have only been 64 100-degree days in Philly since 1894 (per the NWS).
• We've had only one 100+ day in 14 years. That was last June 24, 2025.
• The hottest day on record for Philly is 106 on Aug. 7, 1918.
• The hottest July temperature on record is 104 on July 3, 1966.
• Back-to-back 100-degree days have only occurred 14 times. The last back-to-back 100-degree days were in July 2011.
• Three consecutive 100-degree days have only happened twice in Philly history during July of 1993 and July of 1966.
• We have NEVER had four consecutive 100-degree days.
• Records we are chasing: July 1 record is 102 from 1901, July 2 is 103 from 1901, July 3 is 104 from 1966.