Officials in Lehigh and Northampton counties are urging residents to be careful while temperatures climb to 100 over the next several days.

The Lehigh Valley and surrounding areas will be under an extreme heat warning from Wednesday until Saturday night when highs are expected to be in the upper 90s and low 100s. With humidity, it will feel much warmer.

Officials in both counties are recommending residents stay in air-conditioning as much as possible. In Northampton County, seniors can go to any of the senior centers to cool down during the heat wave.

People should also wear lightweight, light-colored, loose-fitting clothes, as well as a wide-brimmed hat, sunglasses and sunscreen, officials said. Blinds, curtains and shades should be closed during the hottest parts of the day, Lehigh County officials said in a news release.

Older adults, family members, neighbors and anyone else who might be vulnerable to extreme heat should be checked on.

“Knowing what to do to protect yourself and loved ones from extreme heat can save lives,” Jorge Martinez, CEO of the American Red Cross of Greater Pennsylvania, said in a news release. “We’re asking everyone to check on friends and neighbors, especially older adults, people with chronic conditions, outdoor workers and athletes. You could make all the difference by sending a text, making a call or knocking on their door.”

Knowing the signs of heat illness, including heat cramps, heat exhaustion and heat stroke, is important as well, the Red Cross said.

Those suffering from heat cramps will have heavy sweating and muscle pain, and they should rest in a cool place and drink water every 20 minutes, officials said.

Symptoms of heat exhaustion include heavy sweating, weakness, cool and clammy skin, muscle cramps, dizziness, fainting, nausea and vomiting. Those who suffer heat exhaustion should stop what they are doing, get to a cool place and hydrate. They should seek medical attention if they are vomiting or don’t feel better in an hour, according to the Red Cross.

Heat stroke, which can be deadly, is signaled by high body temperature, rapid heartbeat, confusion, headache, dizziness, fainting, nauseua or vomiting. People should call 911 if heat stroke is suspected. Those experiencing heat stroke should move to a cool place and use a wet cloth or cool bath to cool down.

Officials said hydration is very important during the heatwave, and that people should drink a cup of water every 20 minutes, even if they do not feel thirsty. Sugary, caffeinated and alcoholic drinks should be avoided.

The Red Cross said it is monitoring the heat wave, and will respond if needed.

Seniors may go to the following senior centers in Northampton County:

• 520 E. Fourth St., Bethlehem, from 8:30 a.m. to 1:30 p.m.

• 4131 Lehigh Drive, Cherryville, from 9 a.m. until 2 p.m.

• 901 Washington St., Easton, from 9 a.m. to 1 p.m. Tuesday, Wednesday and Thursday

• 15 Wood St., Nazareth, from 8 a.m. until 1:30 p.m.

• 720 Old York Road, Bethlehem, from 9 a.m. until 3 p.m.

• 1800 Sullivan Trail, Suite 140, Easton, from 7:30 a.m. until 3:30 p.m.

• 4 E. Fourth St., Bethlehem from 8 a.m. to 1 p.m.

• 323 Northampton St., Hellertown, from 9:30 a.m. until 2 p.m.

• 707 American Bangor Road, Bangor, from 7:30 a.m. until 3:30 p.m.