An excessive heat warning goes into effect at noon today with heat index values expected to reach triple digits in each of the next three days.

The National Weather Service's latest forecast calls for heat index of 109 today, 113 on Saturday and 104 on Sunday.

The highest values will be in the afternoons, but overnight low temperatures will also be very warm and the air oppressively muggy. Saturday will be the hottest day.

The heat goes comes just as the National Oceanic and Atmospheric Administration Thursday announced that June averaged 60.6 degrees (15.9 Celsius), about 1.7 degrees (0.9 Celsius) warmer than the 20th century average.

It beat out 2016 for the hottest June with records going back to 1880. NASA and other groups also concluded that last month was the hottest June on record.

"Earth is running a fever that won't break thanks to climate change," North Carolina state climatologist Kathie Dello said in an email. "This won't be the last record warm summer month that we will see."

It seems likely that July too will be a record hot month, said Berkeley Earth climate scientist Robert Rohde.

The United States set a record for most precipitation. The 12-month period from July 2018 to June 2019 was the wettest on record.

The first half of 2019 is tied with 2017 for the second hottest initial six months of the year, behind 2016. So far the year is 1.7 degrees warmer than the 20th century average.

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