Heat warnings and advisories were in effect Wednesday for the District of Columbia, Virginia, North and South Carolina, New Jersey, Maryland, Delaware, and parts of Pennsylvania, New York and Georgia, the National Weather Service said.
Business was booming at ice cream shops and water parks.
"The heat is definitely driving people to the water," said Emily Ball, manager at Wild River Country in North Little Rock, Ark.
The weather also has driven up demand for electricity to run fans and air conditioners, straining electric utilities from California to New York, where the New York Independent System Operator said usage hit record levels Tuesday for the second week in a row.
The Tennessee Valley Authority, the nation's largest public utility, said demand in its seven-state region stretching from Mississippi to Virginia hit an all-time record Tuesday of 31,935 megawatts — breaking the record set just the day before. The average temperature across the Tennessee Valley when the record was set Tuesday was 95 degrees.
A cold front promised relief Wednesday for Arkansas and other states. By late Wednesday morning, rain and thunderstorms marking the front stretched from Texas to northern New York state.
The front touched off storms Tuesday that battered parts of northern Ohio with hurricane-force wind. At least 30,000 FirstEnergy Corp. customers were without power Tuesday night.
Cooler air behind the front promised highs only in the 70s Wednesday in northern Ohio and elsewhere in the upper Midwest.
Ahead of the front, however, New York's Central Park cooled only to 80 degrees during the night and headed for a high Wednesday in the upper 90s. Meteorologists warned of a third straight day of dangerously hot and humid weather in parts of the Southeast.
Florence, S.C., hit a record high of 101 on Tuesday, toppling the old record of 99 that had been on the books since 1949, the weather Service said. Raleigh-Durham, N.C., also peaked at a record 101, and Lumberton, N.C., roasted at 102.
The heat has been blamed for at least 28 deaths in the Phoenix area, most of them homeless people, along with at least four in Missouri, two young children left in hot cars in Oklahoma, and one each in Kentucky, Ohio and Mississippi.
The heat also was blamed for at least 1,200 cattle deaths in Nebraska.
Farmers across the Midwest have been using everything from electric fans to cold showers to protect their livestock from the oppressive heat.
Tracy Swank, who raises sheep near Toledo, Ohio, said she has been opening more barn doors to increase air flow and filling more troughs and buckets with water.
"Animals are pretty resilient. They'll adjust, but you still have to give them plenty of water and provide some shade," she said.