Almost 40M Americans under warnings or advisories because of heat

While many Americans along the Gulf Coast are bracing for torrential rain and a possible hurricane, millions of others are dreading the oppressive heat to come in the next few days.

More than 6.5 million people are under an excessive heat warning, including residents of Phoenix, according to the National Weather Service. Above normal temperatures in the Arizona capital could factor into heat indexes close to 120 degrees on Friday and Saturday, CNN meteorologist Dave Hennen said.

On Wednesday the temperature alone was headed toward 110 degrees and Thursday will be hotter, the weather service said.

About 32.9 million people are under a heat advisory in states from Alabama to Texas, the weather service said.

Cities like Dallas, Oklahoma City, Little Rock, Memphis, St Louis and Birmingham could be see 110 to 115 heat indexes, Hennen said.

Medical experts say it is important during heat waves to stay hydrated by drinking plenty of fluids.

But don’t load up on sugary or alcoholic drinks because that would make you lose more body fluid. Don’t be tempted to gulp down cold water as that could cause stomach cramps, according to the CDC.

Make sure your beverage will also replace the salt and minerals you have lost due to sweating — sports drinks can do the job.

CNN’s Nina Avramova contributed to this report.