"Sweaty, it's sweaty out," said one woman in New York's Times Square. "There is not one person in this entire city who is not sweating now."
High temperatures are expected across the country - in St. Louis, Richmond, Tampa, Las Vegas and Houston.
Temperatures well over 90 degrees will be the norm for most of the nation today, reports CBS News correspondent Elaine Quijano. Factor in the humidity, and in many spots it will feel like the hundreds.
In Southern California Friday, lightning-sparked wildfires smoldered and temperatures soared to break records. A 90ºF record high was set in Westwood, breaking the previous record of 87ºF set in 1978. A 1998 record was tied in Long Beach, where the mercury hit 95 degrees. In the San Fernando, San Gabriel and Santa Clarita valleys, the highs soared past 100.
The National Weather Service issued an excessive-heat warning through Saturday night for mountains and valleys.
"It's gonna be bloody hot and humid," weather service spokesman Bill Hoffer said.
Health authorities said officials said a fourth death in central New York State has been attributed to the high temperatures. Dustin Roberts, 23, was found dead in his Seneca Falls apartment by a friend Tuesday, having succumbed to heat stroke.
In Atlantic City, N.J., all bets were off after mechanical problems left some casinos without air conditioning, sending gamblers scrambling for relief.
But along Lake Shore Drive in Chicago, fitness fanatics were undeterred by the sweltering heat, with temperatures hitting above 90 degrees and humidity at nearly 90 percent this week.
Forecasters say the heat is so intense, even in the desert Southwest, temperatures could approach record-setting levels there this weekend.
All of that will make its way East in the coming days - enough heat to make the summer of 2010 a scorcher compared to last year.
"This summer has been a lot hotter," said Bernie Rayno of Accuweather. "The heat has covered a larger area, and we're not done yet.
And for many, that means cool comfort trumps fashion. As our Times Square denizen says, "If you've got a long sleeve shirt that's designer that you want to rock today, don't do it!"
At least the U.S. is not alone: A heat wave across much of Europe is causing crops to wither, forest fires to ignite and roads to melt, while Moscovites are sunbathing.
The air-conditioning systems on board the high-speed trains of Germany's national rail operator Deutsche Bahn broke down several times. With locked windows, dozens of passengers were afflicted with heat exhaustion after spending hours trapped in temperatures of up to 50ºC (122ºF).
U.S. climate scientists said Thursday that June was a record-setting month in the temperature department, keeping the planet on a course for a hot year.
Worldwide, the average temperature in June was 61.1ºF (16.2ºC) - 1.22º F (0.68ºC) warmer than average for the month of June, said the National Oceanic and Atmospheric Administration in Washington. This year has had the warmest average temperature for the January-June period on record - 57.5ºF (12.2ºC).
Russia's worst droughts in a century have destroyed almost 25 million acres of crops in central and
European areas, authorities said. A state of emergency has been declared in 18 Russian provinces, where fire has engulfed more than 64,000 acres of forest.
Germany's Potato Industry Union, meanwhile, said it expects losses of 30 percent in this year's harvest.
"The situation is worse in many places this year than in the drought years of 2003 and 2006," said Martin Umhau, the head of Germany's Union of Potato Industry.
Meanwhile, drowning deaths were up in Eastern Europe as people flocked to seas, lakes and rivers in search of a break from the blistering heat. More than 230 people died in the last week alone across Russia, with 21 perishing over two weeks in Latvia, according to officials, who lamented the tendency of heavy drinking while sunbathing. Last year, about 3,000 people drowned in Russia.
Blood reserves were dropping in Germany, with fewer donors able to travel to blood banks.
"We now only have reserves for one to three days," German Red Cross spokesman Friedrich-Ernst Dueppe told the news agency DAPD.