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About half the country is under active heat advisories on Monday, affecting more than 198 million Americans, according to . 

The extreme heat is expected in the Midwest, the Southeast and some parts of the Northeast. The heat alerts will remain in effect through Wednesday night in some places.

Many areas have already been experiencing heat waves. Tampa, Florida, usually cooled down by a sea breeze, hit a record high of 100 degrees on Sunday, .

Temperatures on Monday are forecast to be in the high 90s for multiple cities with feels-like temperatures over 100 degrees.  

Health-related illnesses can increase significantly during extreme heat. It's advised to drink plenty of water and stay in air-conditioned rooms, meteorologists said.

Some northern Midwest states also face severe storm threats on Monday. A derecho, an intense line of fast-moving thunderstorms, is expected early in the evening over parts of eastern South Dakota, .

It's then expected to move into parts of southern Minnesota and northern Iowa.

"Several wind gusts in excess of 75 mph, a few line-embedded tornadoes and instances of severe hail are also probable, according to the Storm Prediction Center," the NWS said.