PHILADELPHIA — The first big heat wave of the summer is here, bearing down on all parts of the U.S., following temperatures that blistered the West Coast in June. Typically heat waves occur twice every summer. Meteorology director Jeff Masters of Weather Underground says expect the current bout of oppressive heat to last a bit longer than the usual three days. Look for relief by Saturday.

1. HEAT WAVE HIGHLIGHTS. Temperatures in the Northeast are five to ten degrees above normal, with New York City experiencing the highest above-normal temperatures of any place in the country. The hottest summer in U.S. history — an average 73.83 degrees for the season — occurred during the Dust Bowl in 1936. The 2011 and 2012 summers tied for second hottest but were only one-tenth of a degree cooler than the record.

2. ODD BEHAVIOR. While the Northeast is burning up, Texas and Oklahoma recorded their all-time lowest temperatures for July 15. And in parts of Alaska, the readings were warmer Monday than parts of Texas. Alaska’s eastern interior was in the low 80s, while Abeline, Texas, recorded a cool 68 degrees.

3. BAD HAIR WEEK. Besides making everyone uncomfortable, humidity is hard on a hairdo. Curly hair tends to frizz and flat hair tends to get, well, flatter. Alyssa Johnson of Pulse Beauty Academy near Philadelphia says the solution is to use special hair products to “seal” hair against the dense, moist air.

4. BASEBALL’S HOT AIR STATS. It is not a myth but a matter of physics that baseballs fly farther in hot, humid air. Physics professor Alan Nathan of the University of Illinois at Urbana-Champaign, explains. “The higher the temperature, the less air resistance, so the ball flies farther.” Each increase in temperature by 10 degrees can increase the flight of a ball by 2.5 to 3 feet. A ball hit during the heat wave could fly 15 feet farther than a ball hit in 40-degree weather in, say, April in Chicago.

5. HOT PHONES NOT SO SMART. Most smartphones are designed to withstand extreme temperatures — many of them shut themselves down when they sense too much heat. But the batteries that power phones are still fairly vulnerable. Engineering professor Yury Gogotsi at Drexel University says high temperatures can cause batteries to die faster than normal and can lower a battery’s life expectancy.