(NEW YORK) — As Tropical Storm Fred takes aim on the Florida Keys, a heat wave is gripping 33 states.

Heat wave

A heat wave is spreading to the Northeast as well as parts of the Midwest, South and Pacific Northwest.

By Thursday, the heat index — what the temperature feels like — could climb to 103 degrees in Boston, 105 in New York City and 109 in Philadelphia.

Excessive heat warnings have been issued in New York City and Philadelphia. Boston has declared a heat emergency Wednesday through Friday.

“When it is this dangerously hot during the day and the temperatures do not drop at night, your body doesn’t have time to recover,” Boston Mayor Kim Janey said. “I am urging everyone to drink lots of water and find ways to stay cool. Anyone who needs a place to beat the heat can come inside and rest in the air conditioning at one of our cooling centers.”

The dangerously high temperatures are also reaching cities including Chicago, Memphis, Dallas, Portland and Sacramento.

Tropical Storm Fred

Tropical Storm Fred formed overnight near Puerto Rico, where gusty winds and heavy rain are hitting through the morning.

A tropical storm warning is in effect for the Dominican Republic, where Fred is expected to reach Wednesday afternoon.

A tropical storm watch was issued for the southern Bahamas for Thursday and Thursday night.

By Friday night into Saturday morning, Fred is expected to move over the Florida Keys with heavy rain and gusty winds.

It’s possible Fred could strengthen as it heads into the Gulf of Mexico Saturday night into Sunday, though the forecast could change in the next few days.

Copyright © 2021, ABC Audio. All rights reserved.