ARLINGTON, Va. − Excessive heat advisories, watches and warnings blanketed the first day of summer Thursday for more than 100 million Americans from Chicago to Caribou, Maine − where it was even too hot for soft ice cream.

Meteorologists are blaming a heat dome, a powerful high-pressure system that traps hot air over a region and prevents cool air from getting in while causing ground temperatures to remain high.

The searing heat rolling across the northeastern tier will make its way to the mid-Atlantic in coming days. This Washington, D.C., suburb is facing the prospect of 100 degrees by Sunday. High temperatures here are forecast to remain above 90 degrees for the next two weeks.

New England is under siege. The National Weather Service forecast a high of 98 degrees for a second consecutive day in Boston. The same temperature on Wednesday broke a record of 96 degrees for the date that stood for more than 100 years. Worcester, Massachusetts, and Providence, Rhode Island, also broke 100-year-old records, and Hartford, Connecticut, was forecast to see 97 degrees, one day after the same temperature broke a record of 95 set in 1995.

"Millions (are) at the mercy of a prolonged stretch of 90-degree Fahrenheit temperature," AccuWeather Meteorologist Renee Duff said. "The longevity of the intense heat will put additional strain on residents and electrical infrastructure."

Developments:

∎ In New York City, Mayor Eric Adams was opening cooling centers − and promoting local parks. "Temperatures are still rising, so find safe ways to stay cool," he said in a social media post. "@NYCParks provide great options from our beautiful beaches to refreshing sprinklers and shady benches."

∎ The temperature in and around Pittsburgh could feel like 110 degrees through Saturday. The heat index in northwest Ohio and northern Indiana could reach 102 through Friday.

∎ Kroger supermarkets are providing a great way to cool off. To celebrate the official start of the summer season, Kroger is giving away 45,000 pints of ice cream. Visit FreeKrogerIceCream.com and download a limited-time, single-use digital coupon available only on Thursday while supplies last.

Here comes the heat:Cities have been getting ready for the heat onslaught

Too hot for soft ice cream in Caribou, Maine

Caribou, Maine, near the Canadian border, has been in the news the last few days for its soaring heat index, which surpassed 103 degrees Wednesday and easily bested an almost 50-year record of 101 degrees. Hannah Embelton, 22, who serves ice cream at a local shop, told the Associated Press her customers were staying away from soft serve because it melts too quickly.

“We usually never get the brunt of all this heat and humidity because we are so north," she said. "How hot it is − that is all everyone is talking about.”

World could again break record for heat this summer

The dangerous heat is not limited to the United States. Cities on four continents are scorching, an early sign that a season of record-breaking heat could surpass last summer as the warmest in 2,000 years. The World Meteorological Organization says there is an 86% chance that one of the next five years will eclipse 2023 to become the warmest on record.

In Saudi Arabia, where nearly 2 million Muslim pilgrims are finishing the haj in Mecca this week, hundreds have died during the journey amid temperatures 120 degrees. Egyptian medical and security sources said Thursday that at least 530 Egyptians alone had died.

In India, New Delhi on Wednesday registered its warmest night in at least 55 years, with India's Safdarjung Observatory reporting a temperature of 95.4 degrees at 1 a.m.

Alberto makes landfall in Mexico

Tropical Storm Alberto, the first named storm of 2024, made landfall in Mexico and was 25 miles wes ot the Mexican town of Tampico and 255 miles south of Brownsville, Texas, at 8 a.m. ET Thursday, according to the National Hurricane Center. It was rolling west at 13 mph, driving 45 mph winds. Three deaths in Mexico were blamed on the storm. But officials there were also crediting Alberto which delivering much-needed rains to the drought strickent region. 

Along with sustained winds near 45 mph, the storm is forecast to dump up to 20 inches across parts of northeast Mexico with nearly a foot of rain expected throughout southern Texas. Such high rainfall totals will likely produce "considerable flash flooding and urban flooding" as well as possible mudslides across northern Mexico, the NHC said.

Tropical Storm Alberto makes landfallin Mexico; danger looms for Texas

How do you stay safe in the heat?

The weather service is urging people to avoid the outdoors in the heat of the day. If that isn't an option, look for shade and drink plenty of water. Temperatures inside closed-up cars can reach deadly heights in minutes, so children and pets absolutely cannot be left in them.

People at greatest risk are young children, elderly people, outdoor workers and those with chronic diseases, mental illness or people taking certain medications that make it difficult to regulate their body temperatures, experts say. Additionally, those without access to reliable AC are at risk, as are others who live in areas called urban heat islands that have little green space and are warmer because of more pavement and buildings.

− Michael Loria

Here's how to keep cool:Stay safe during this week's heat wave that is hitting millions

Contributing: Christopher Cann, USA TODAY; Reuters