The summer heat is intensifying, so hot that forecasters put nearly 100 million Americans under extreme heat warnings or advisories this week.

Forecasters say Arkansas, Louisiana, Oklahoma, Tennessee and Texas are expected to bear the brunt of the highest temperatures.

According to the weather service, "extreme heat" will continue throughout the week and spread across the northeast on Wednesday.Most of the extreme heat warnings cover most of the Southern Plains and the lower Mississippi River valley.Several heat advisories have also been put in place for parts of the Northeast, from Philadelphia to Boston. In those areas, the heat index is expected to reach 100 degrees.

In addition to higher temperatures, the risk of fire is also increasing in many states. The Weather Service placed parts of Louisiana, Nebraska, Oklahoma and Texas under red flag warning. These warnings mean that weather conditions, such as high heat, low humidity and strong winds, are providing the perfect mix for wildfires with dry vegetation that can rapidly spiral out of control.

The weather service is advising people to take extra precautions when going out and do things like drinking plenty of fluids, staying in air-conditioned rooms and out of the sun.