Triple-digit temperatures prompted more heat advisories across much of the southern U.S. on Sunday, triggered severe thunderstorms that knocked out power to hundreds of thousands of people from Oklahoma to Mississippi and produced gusty winds that raised wildfire threats in Arizona and New Mexico.

A suspected tornado struck near Scranton, Arkansas early Sunday, destroying chicken houses and toppling trees onto houses, the National Weather Service said. There were no immediate reports of serious injuries.

Louisiana Gov. John Bel Edwards declared a state of emergency for north and central Louisiana after strong winds and severe weather caused widespread power outages on Saturday. On Sunday, indicated more than 740,000 people were without power in Oklahoma, Texas, Louisiana, Arkansas, and Mississippi, according to PowerOutage.us.

The National Weather Service warned that potentially record-breaking temperatures would continue over southern Texas and the western and central Gulf Coast and that storms producing damaging winds, hail and possibly tornadoes could strike the lower Mississippi Valley.

In Florida, the weather service issued another heat advisory Sunday, this time mainly for the Florida Keys. Forecasters said heat index readings – the combination of high temperatures and oppressive humidity – could reach between 108 degrees Fahrenheit (42 Celsius) and 112 degrees (45 C) in places such as Key Largo, Marathon and Key West.

“These conditions will cause increased risk of heat illness for people outdoors or in non-air conditioned spaces,” the weather service said in a bulletin.

In the Southwest, where fire crews are battling multiple wildfires in Arizona and New Mexico, forecasters said triple-digit temperatures and gusty winds would lead to critical fire weather over the next couple of days. Sunday promised to be the hottest day of the year in Arizona, with highs up to 110 degrees (43.5 C) in Phoenix.

Winds were forecast to gust from 30 mph to 40 mph (48-64 kph) on Sunday east of Flagstaff, Arizona along the Interstate 40 corridor and up to 50 mph (80 kph) on Monday, creating potentially critical fire weather across much of northeast New Mexico.

A large brush fire that broke out Friday afternoon south of Tucson, Arizona shut down a state highway on Saturday. Arizona 83 reopened on Sunday and no homes were in immediate danger, authorities said.

Much of Nevada was under a high-wind advisory with gusts up to 55 mph (88 kph) with blowing dust that could hamper visibility on highways, the weather service said.

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Associated Press writers Kim Chandler in Montgomery, Alabama and Curt Anderson in St. Petersburg, Florida contributed to this report.

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