"Dangerous heat continues over Texas, before building into neighboring states beginning Wednesday. Through next Monday, heat indices upwards of 120 degrees [Fahrenheit] and little overnight relief can be expected," the Weather Prediction Center said.
The dangerous heat will continue across much of Texas this weekend, with more widespread sweltering heat impacting most of the southern and south-central United States next week into at least the first few days of July, it said.
Meteorologists said the sweltering temperatures are due to a "heat dome," caused when a ridge of high pressure builds over an area, holding air inside as temperatures warm, resulting in what they describe as "uncomfortable or even dangerous levels," it said.
More than 55 million people from southern Arizona to the Florida coast are affected by the heat wave, with excessive heat warnings having been declared in cities including Baton Rouge and New Orleans, Louisiana, and Dallas, Texas, it added.
The dangerous heat wave will continue into the beginning of the July 4 holiday week, experts said, according to the Weather Prediction Center.
The weather events come as more than 3,600 flights were either canceled or delayed over severe weather, according to data provided by the FlightAware portal.
"Total delays within, into, or out of the United States today: 2,170. Total cancellations today: 1,473," the portal said.
Newark Liberty Airport near New York City continues to face the most significant challenges, as over 350 in- and outbound flights were canceled and more than 150 delayed, according to the tracker.
The US National Weather Service has warned of the possibility of severe thunderstorms across the United States. There is a "slight risk" of excessive rainfall over parts of the Northern Mid-Atlantic, it added.