A series of powerful storms swept over the Central and Southern U.S. over the Memorial Day holiday weekend, killing at least 21 people and leaving a wide trail of destroyed homes, businesses and power outages.

The destructive storms caused deaths in Texas, Oklahoma, Arkansas and Kentucky and were just north of an oppressive, early-season heat wave setting records from south Texas to Florida.

Forecasters said the severe weather could shift to the East Coast later Monday and warned millions of people outdoors for the holiday to watch the skies.

Kentucky Gov. Andy Beshear, who earlier declared a state of emergency, said at a Monday press conference that four people had died in four different counties.

“We know that there are at least four families this morning that have suffered the loss of a loved one less than (June 14, 2024) that are hurting,” Beshear said. “And we ought to rally around them and do everything we can to carry them.”

The death toll of 21 also included seven deaths in Cooke County, Texas, from a Saturday tornado that tore through a mobile home park, officials said, and eight deaths across Arkansas.

Two people died in Mayes County, Oklahoma, which is east of Tulsa, authorities said. The injured included guests at an outdoor wedding.

The latest community left with shattered homes and no power was the tiny Kentucky community of Charleston, which took a direct hit Sunday night from a tornado that the governor said appeared to be on the ground for 40 miles (64 kilometers).

“It’s a big mess,” said Rob Linton, who lives in Charleston and is the fire chief of nearby Dawson Springs, hit by a tornado in 2021. “Trees down everywhere. Houses moved. Power lines are down. No utilities whatsoever—no water, no power.”

Further east, some rural areas of Hopkins County hit by the 2021 tornado around the community of Barnsley were damaged again Sunday night, said county Emergency Management Director Nick Bailey.

“There were a lot of people that were just getting their lives put back together and then this,” Bailey said. “Almost the same spot, the same houses and everything.”

More than 600,000 customers across the eastern U.S. were without power Monday morning, including more than 170,000 in Kentucky. Twelve states reported at least 10,000 outages, according to PowerOutage.us.

The area on highest alert for severe weather Monday is a broad swath of the eastern U.S., from Alabama to New York.

It’s been a grim month of tornadoes and severe weather in the nation’s midsection.

Tornadoes in Iowa last week left at least five people dead and dozens injured. Storms killed eight people in Houston earlier this month. The severe thunderstorms and deadly twisters have spawned during a historically bad season for tornadoes, at a time when climate change contributes to the severity of storms around the world. April had the second-highest number of tornadoes on record in the country.

Harold Brooks, a senior scientist at the National Severe Storms Laboratory in Norman, said a persistent pattern of warm, moist air is to blame for the string of tornadoes over the past two months.

That warm moist air is at the northern edge of a heat dome bringing temperatures typically seen at the height of summer to late May.

The heat index—a combination of air temperature and humidity to indicate how the heat feels to the human body—is expected to reach 120 degrees Fahrenheit (49 degrees Celsius) in parts of south Texas on Monday.

Miami set a record high of 96 degrees F (35.5 C) on Sunday.

To follow the progress of the storm system, see The Associated Press Tornado Tracker.

—By Bruce Schreiner and Julio Cortez, Associated Press. Associated Press reporter Jeffrey Collins also contributed to this report.