A few days after the official arrival of summer, extreme heat began to bake much of Maine on Monday, with temperatures expected to rise further Tuesday, prompting warnings from forecasters and the opening of cooling centers across the state.

The National Weather Service said much of inland Maine was under a heat advisory Monday, while a more serious extreme heat watch was set to go into effect Tuesday, when the heat index is forecast to reach over 100 in many areas.

Kennebec County is expected to be one of the hotter areas, Jon Palmer, a meteorologist with the National Weather Service in Gray said.

Tuesday is expected to reach 98 degrees in central Maine, with the heat index value — what the temperature actually feels like — as high as 106 degrees.

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“The sea breeze is not really going to be present,” he said. “The heat is going to expand all the way to the coast and we are going to see a high heat index even in Portland and Portsmouth and portions of the Midcoast. The hottest areas are going to be around Kennebec County in Augusta, Waterville.”

Parts of Cumberland and Oxford counties were under a heat advisory until 8 p.m. Monday, the weather service said. Inland temperatures Monday were expected to hover around 90, with heat indexes nearing 100 thanks to humidity, while coastal temperatures were nearer to 80.

STAYING SAFE

To stay safe during these dangerous temperatures, the Red Cross recommends three essential actions: stay hydrated, stay cool and stay connected.

Drink a cup of water every hour, and if working or spending time in the sun, drink one cup of water every 20 minutes and take breaks in the shade.

Staying connected involves checking in on family, friends and pets to ensure they have access to water and shade, or asking others for help if needed. The Red Cross said checking in can be as simple as a text or call.

The Red Cross and National Weather Service both warned Mainers to look for signs of heat exhaustion or heat stroke.

“Once you start to get to the point where you feel like you [don’t] have the ability to sweat anymore, that is one of the warning signs,” said Chris Legro, a meteorologist at the National Weather Service office in Gray.

Other warning signs include a headache that won’t go away or simply not being able to remember the last time you hydrated, especially if outside for an extended period, Legro said.

Everyone should take precautions in extreme heat — which is the leading cause of weather-related deaths, according to the World Health Organization — but those with preexisting health conditions, children and older adults should take extra care, Legro said.

Pets can also experience heat illnesses, and Mainers can help prevent them by keeping their pets out of parked cars and ensuring they are hydrated and in cool areas.

Symptoms of heat illness in pets can include heavier panting, difficulty breathing, weakness and increased heart rate, according to the American Society for the Prevention of Cruelty to Animals.

Mainers should also avoid taking their pets out on hot asphalt, which can burn paws, or on long walks that can overheat them.

PLACES TO COOL OFF

Avoiding long exposure to the temperatures and staying inside with air conditioning is crucial. If there is no A/C at home — a common situation for many Mainers — the Red Cross recommends going to someplace like the mall, a library or a cooling center. Mainers can also make use of swimming holes, movie theaters or even beer caves at local convenience stores.

Cooling centers are established during extreme heat warnings and are in large, air-conditioned public buildings to allow community members to escape the heat, charge their devices, and access water and restrooms. Some offer places to shower, and many — especially libraries — have free Wi-Fi.

The Maine Emergency Management Agency lists cooling centers on its website. Here is a list of several across Maine that are open this week:

Androscoggin County

• Auburn Community Resource Center, 121 Mill St., Auburn – Open Tuesday from 9 a.m. to 3 p.m. and Wednesday from 9 a.m. to 1 p.m., offering cooling
• Auburn Public Library, 49 Spring St., Auburn – Open Monday until 7 p.m. and Tuesday and Wednesday from 9 a.m. to 6 p.m., offering cooling
• Auburn Senior Community Center, 48 Pettengill Park Road, Auburn – Open Tuesday from 8 a.m. to 8 p.m., offering cooling
• Auburn Recreation Hasty Gymnasium, 48 Pettengill Park Road, Auburn – Open Wednesday from 8 a.m. to 4:30 p.m.
• Durham Eureka Community Center, 606 Hallowell Road, Durham – Open Tuesday from 8 a.m. to 8 p.m., offering cooling, charging and water
• Lisbon Police Department lobby, 300 Lisbon St., Lisbon – Open as needed 24/7, offering cooling, charging and water
• Redemption Hill Church, 64 Lisbon St. (enter from Park Street door), Lewiston – Open Tuesday from 8 a.m. to 6 p.m., offering cooling

Kennebec County

• Augusta Civic Center, Cumberland Room, 76 Community Drive, Augusta – Open Tuesday from 9 a.m. to 5 p.m., offering cooling
• Waterville City Hall Annex, 46 Front St., Waterville – Open Tuesday from 10 a.m. to 6 p.m., offering cooling

Knox County

• Flanagan Community Center, 61 Limerock St., Rockland – Open Monday and Tuesday from 12 p.m. to 8 p.m., offering cooling
• South Thomaston Public Library, 54 Spruce Head Rd. – Open Monday from 12 p.m. to 4 p.m. and Tuesday and Wednesday from 12 p.m. to 7 p.m., offering cooling
• Rockland Public Library, 80 Union St., Rockland – Open Monday and Tuesday from 10 a.m. to 8 p.m., offering cooling
• Rockland Town Hall, 270 Pleasant St., Rockland – Open Monday and Tuesday from 7:30 a.m. to 5 p.m., offering cooling
• Union Town Office, 567 Common Road, Union – Open Monday through Wednesday from 8 a.m. to 4 p.m., offering cooling

Lincoln County

• Boothbay Harbor Town Office meeting room, 11 Howard St., Boothbay Harbor – Open Tuesday from 8:30 a.m. to 4:30 p.m. and Wednesday from 8:30 a.m. to 12 p.m., offering cooling, water and seating
• Central Lincoln County YMCA Cooling Center, 575 Maine St., Damariscotta – Open Monday through Friday from 5 a.m. to 8 p.m., offering cooling, Wi-Fi and games
• Newcastle Fire Station Community Room, 86 River Road, Newcastle – Open Monday until 7 p.m., offering cooling, bathrooms, water and Wi-Fi

Oxford County

• Canton Town Office meeting room, 94 Turner St., Canton – Open Monday and Wednesday from 8 a.m. to 4 p.m., Tuesday and Friday from 8 a.m. to 12 p.m. and Thursday from 8 a.m. to 6 p.m., offering cooling

Sagadahoc County

• Topsham Town Hall, Russell Room, 100 Main St., Topsham – Open Tuesday from 8:30 a.m. to 4:30 p.m., offering cooling and charging.

Staff Writer Emily Duggan contributed to this report.