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Punishing heat expands with 216 million people in America expected to endure temps of 90 or above

New York City could endure its longest heat wave since 2013, and Philadelphia is forecast to hit 100 degrees for the first time in 10 years.

The punishing heat expands its footprint Thursday, with heat alerts now up for more locations across the mid-Atlantic, including Washington, and the desert Southwest, including Phoenix.

These heat alerts encompass 97 million people.

When factoring in the number of people who will experience highs above 90 Thursday, including those outside the heat alerts, that number skyrockets to 216 million.

For parts of the Plains, high temperatures will climb above 100 once again for cities such as Dallas, Oklahoma City and Houston. Across the South, high temperatures in the upper 90s to near 100 degrees combined with high humidity will lead to heat index values of 110-115. And across the mid-Atlantic and the Northeast, highs in the mid-90s combined with high humidity will lead to heat index values of 98-108.

The soaring temperatures will also result in records being set. Thursday through Saturday, record highs will be possible for cities such as Houston, Memphis, Tennessee, and San Antonio.

On Sunday, numerous records will be possible across the Northeast including Washington, Philadelphia, New York and Providence, Rhode Island.

Heading into the weekend, while some regions will get a break from the heat, other regions, like the southern Plains, won't feel relief anytime soon.

For the Midwest, temperatures will climb into the weekend but a cooling trend arrives Sunday into early next week.

Across the Northeast and New England, the heat wave will last the next five days but breaks on Tuesday.

New York City may face its longest heat wave in a decade. The last time the city saw seven straight days in the 90s was in 2013.

Philadelphia is forecast to hit 100 degrees Sunday (which would set a daily record high), and when combined with the high humidity, it will make it feel more like 105 degrees. The last time Philadelphia hit 100 degrees was in July 2012.

Further south, for cities like Dallas, the heat will extend through next week with no real end in sight.

While the combination of heat and humidity is dangerous on its own, it's helping to fuel life-threatening flash flooding and the risk for severe thunderstorms.

Early Thursday, a compact cluster of thunderstorms trained over parts of northern Tennessee, including the Knoxville area, where 2 to 8 inches of rain fell in a short amount of time sparking flash flooding and water rescues. That cluster of storms is forecast to move south into northern Georgia through Thursday morning, where additional flash flooding is a concern.

In addition to the isolated flash flood threat from slow-moving thunderstorms, strong to severe storms will also be possible the next three days.

On Thursday, 26 million people are at risk for severe storms across two areas, New England and the Southeast. Hail and high winds will be the greatest risks, but an isolated tornado cannot be ruled out.

On Friday, pockets of strong storms could impact portions of the Midwest and the Northeast.

By Saturday, there could be a significant severe weather event for 12 million people across parts of the Great Lakes and the Upper Midwest. Very large hail, significant damaging winds and tornadoes will all be possible.