Heat wave and extreme weather hold U.S. in their grip, killing at least 13 in the Midwest (VIDEO)

A heat wave that has the U.S. in its grip has been responsible for at least 13 deaths in the Midwest so far, according to msnbc. The extreme heat, coupled with stifling humidity, is moving toward the East Coast and is expected to hover over the country at least until the weekend, AFP reported.

The National Weather Service put 18 states under a heat warning, watch or advisory, with the heat index, a combination of temperature and humidity, exceeding 100 degrees Fahrenheit in most places, according to BBC News.

In the Midwestern Great Lakes region, extreme highs are expected for Wednesday and Thursday.

More than 1,000 heat records in the U.S. have been broken this month, according to officials.

According to msnbc:

"This is unusual," said Pat Slattery, spokesman for the Weather Service. "There's no sugar-coating anything here."

A stagnant air mass over the central plains is the cause of the extended heat-wave, which has been hammering the country, according to the National Weather Service.

An increase in deaths of illegal immigrants crossing the border into the U.S. from Mexico has also been blamed on high temperatures, the U.S. Border Patrol said.

Roads in Oklahoma were reported to be buckling in the extreme heat, and that state had its 38th day of triple-digit temperatures so far this year on Monday.

The Midwestern states of Illinois and Indiana were bracing for temperatures and humidity indices above 115 degrees Fahrenheit, after the heat index on Monday reached 124 degrees Fahrenheit in some parts of northwestern Illinois, according to AFP. On Wednesday, Chicago is expecting a heat index above 105 degrees, an unusual occurrence.

According to ABC News, the heat is affecting poor and homeless people in particular across the Midwest. In Minneapolis, the Salvation Army's Harbor Light Center provides people who need it refuge in air conditioning or water to rehydrate them. Chicago is taking special precautions after a heat wave in 1995 killed more than 700 people in less than a week. If temperatures rise above 90 degrees now, an emergency plan kicks in; the plan includes visits to the elderly and others who are particularly vulnerable. City officials also offer rides to one of Chicago's six cooling centers.

The National Weather Service is also reporting that severe thunderstorms, hail and high winds are possible through the weekend, AFP said.

In Arizona, dust storms sweeping through Pinal and Maricopa counties in the Phoenix area on Monday evening towered nearly 4,000 feet high, caused airplane flight delays and left 2,300 people without electricity, according to Arizona Central.

The storms moved at about 10 to 20 miles per hour and cut visibility in some areas to as low as 60 feet, according to the National Weather Service. Meteorologists said the dust storm was between 3,000 and 4,000 feet high.

In Minnesota, normally a temperate state, heat indexes hit 122 degrees Fahrenheit, BBC News reported.

Last month, NOAA released data showing that 30-year temperatures across the U.S. had risen by about 1.5 degrees Fahrenheit, according to AFP:

"The climate of the 2000s is about 1.5 degree Fahrenheit warmer than the 1970s," said Thomas Karl, director of NOAA's National Climatic Data Center.

Forecasters said the heat wave was likely to hang on through the the end of the month.