Heat wave moving Northeast!

• The heat index is expected to exceed 105 degrees in 23 states
• Heat advisories are expected to last through at least Tuesday
• Excessive heat is extremely hazardous to human health
• Heat-related death reported in Illinois

(CNN) -- A dangerous heat wave slowly began to ease in the nation's heartland even as it spread into the Northeast, the National Weather Service said.

Twenty-three states and the District of Columbia were under heat advisories Tuesday.

Excessive heat warnings are in place from western Oklahoma to Connecticut, and from the Deep South to the Ohio Valley.

In these areas, the heat index, or how hot the body feels due to the combined effects of heat and humidity, will reach between 110 and 115 degrees this week.

Stillwater, Oklahoma, and Fort Smith, Arkansas, notched Monday's high temperatures across the United States, topping at 107 degrees, the weather service said. At least a dozen cities, hit the century mark, with many others well into the 90s.

A 51-year-old man in Granite City, Illinois, died Sunday due to the excessive heat, the Madison County coroner said. Mitsunari Uechi was found unresponsive in his mobile home, where the air conditioning was not working. Police described the residence as "extremely hot," Coroner Stephen Nonn said in a statement.

Uechi was transported to Gateway Regional Medical Center with a body temperature of 104 degrees. He was later pronounced dead, according to the coroner.

Nonn noted that Uechi "suffered from chronic medical problems that placed him in a higher risk for heat-stress related illness."

Several high-temperature records have been broken recently.

Wichita, Kansas, hit 111 degrees Sunday. The National Weather Service says temperatures of 111 degrees have occurred there only 10 times since July 1888.

High pressure over the Plains is keeping the weather pattern stable, allowing heat to build and expand up the Eastern Seaboard.

Some relief is expected by midweek as the high pressure system weakens and shifts slightly southeast. This will allow thunderstorms to develop in the central Plains.

Excessive heat is extremely hazardous to human health. According to information on the National Weather Service website, heat disorders can develop when the body heats too quickly to cool itself safely, or when a person loses too much fluid or salt by sweating or dehydration.

Signs of heat exhaustion include heavy sweating, pale and clammy skin, weak pulse, fainting and vomiting.

The agency suggests that people protect themselves from heat disorders by reducing activity during the hottest part of the day, wearing lightweight clothing and drinking plenty of water.

The agency also asks that people abstain from caffeinated or alcoholic drinks. Even meat and other proteins can increase metabolic heat production.

The states under heat advisory are:

-- Alabama -- Arkansas -- Connecticut -- Delaware -- Georgia -- Illinois -- Indiana -- Kansas -- Kentucky -- Louisiana -- Maryland -- Mississippi -- Missouri -- New Jersey -- New York -- North Carolina -- Ohio -- Oklahoma -- Pennsylvania -- South Carolina -- Tennessee -- Texas -- Virginia