Philadelphia is entering the most dangerous phase of a period of extreme heat that started Wednesday.

Here’s what you need to know about the hot weather.

The forecast

The National Weather Service has extended an excessive heat warning beyond the region’s urban core to cover Eastern Pennsylvania and all of New Jersey and Delaware. It is in effect until 10 p.m. Sunday.

The service says the most-dangerous heat and humidity will occur from mid-afternoon into the early evening each day for the next three days. And don’t expect any real relief at the Jersey Shore.

Heat index values area expected to be in the 102- to 107-degree range Friday afternoon and the 108- to 113-degree range on Saturday afternoon and Sunday afternoon.

The air temperature could hit 100 degrees on Saturday for the first time in seven years in Philadelphia.

A cold front packing thunderstorms and potentially heavy rainfall should bring relief by Tuesday.

Utilities

Are utilities are bracing for a surge in electricity usage. Money-saving tips, courtesy of PSE&G and NRG, include:

  • Don’t cool an empty house or business. Set your thermostat higher when you are away.
  • Close blinds and draperies facing the sun to keep out the sun’s heat.
  • Don’t cool unused rooms. Close the vents and shut the door.
  • Ceiling fans cool fast and cost less than air conditioning. In hot weather, set your ceiling fan to spin quickly and counterclockwise (to push air downward toward the floor.)
  • Set your air conditioner fan to the “auto” rather than “on” position.
  • Use the microwave and toaster oven to cook or warm food, or grill outside. Using the oven in the heat of summer forces your air conditioner to work harder.
  • Seal holes and cracks around doors and windows with caulk or weather-stripping.
  • Check air filters replace as necessary.

Staying cool

Residents are urged to drink plenty of fluids, stay in air-conditioned rooms, stay out of the sun, and check up on relatives and neighbors.

“We strongly urge the public to visit older friends, relatives and neighbors to ensure that air conditioners or fans are working and homes are adequately ventilated. In a heat wave, the majority of the victims are older people and those with pre-existing medical conditions,” Health Commissioner Thomas Farley said.

Due to the excessive heat, all public pools in Philadelphia will operate on a free swim schedule until further notice. A listing of all public pools in Philly can be found here.

Heading to the Shore? Check out which New Jersey and Delaware beaches are open, and which are closed or under advisory.

Some neighborhoods get hotter than others, too. Using a map the Inquirer published last summer, you can see which Philly neighborhoods tend to be warmer or cooler than others, due to a number of factors.

Heat health emergency

Philadelphia has declared a heat health emergency. In these situations — the current heat emergency is in place through 11 p.m. Monday — the city activates several tools to aid residents.

During a heat health emergency, you can call the city’s Heatline, a special helpline number, at 215-765-9040. Operators will give you tips for staying cool and you can talk to health department nurses about heat-related issues.

Some cooling centers — like recreation centers, libraries, and senior centers — will also stay open later during a heat health emergency. Find your nearest center here.

Additionally, residential utility shutoffs are discontinued until the emergency passes.

A heat health emergency was last in effect in Philly in July 2018.

Signs of heat-related illness

Early warning signals:

  • Decreased energy, loss of appetite, faintness, lightheadedness, and nausea
  • People experiencing these symptoms should go to a cool environment, drink fluids, remove excess clothing, and rest.

Serious signs of heat stress:

  • Unconsciousness, rapid heartbeat, throbbing headache, dry skin, chest pain, mental confusion, irritability, vomiting, diarrhea, muscle cramps, staggering, and difficulty breathing.
  • People experiencing these symptoms should get immediate medical attention. While waiting for help, move the person to a cool area, remove excess clothing, spray with water, and fan the person.

Transportation

Extreme heat also can have an impact on transportation, particularly overhead power lines that supply electricity to SEPTA Regional Rail, N.J. Transit, and Amtrak trains.

No major problems have been reported.

SEPTA said that for passenger convenience due to the heat, there will be no A-B skip/stop service this week on the Market-Frankford Line. SEPTA has also done this in periods of extreme cold.

Helping out

Prolonged heat waves can be especially dangerous for people living on the street. The city urges residents to call 215-232-1984 if they see someone who needs shelter from the heat or other homeless services.

Pets

Also remember that the heat can affect pets and that it is against the law in Philadelphia to leave dogs outside without protection from the sun when it’s hot.

Staying in the loop

You can get notified of a heat health emergency and other city alerts through the city’s free text notifications, ReadyPhiladelphia. Text READYPHILA to 888-777 to sign up.