As the great Glenn Frey once sang: The heat is on.

The National Weather Service issued an excessive heat warning for most of Massachusetts that will be in effect from noon Friday until 8 p.m. Sunday.

“Saturday and Sunday will be the major scorchers,” forecasters tweeted.

Temperatures will reach the upper 80s to lower 90s Friday and then increase to upwards of 100 degrees on Saturday and Sunday, according to the weather service.

“It will not cool off much overnight, with lows in most areas only dropping to the mid 70s to near 80,” forecasters wrote.

With dewpoints in the 70s, it’s going to be humid, and forecasters said the heat index values — which is how hot it actually feels — will range from 90 to 100 on Friday and then climb to as high as 112 degrees over the weekend.


In the Boston area, Saturday will be mostly sunny and hot, with highs in the upper 90s and heat index values of up to 105 degrees. Sunday will be partly sunny with a chance of showers, with highs around 97 and heat index values of up to a sizzling 107 degrees.

The weather service said to take extra precautions if you spend time outside.

“When possible, reschedule strenuous activities to early morning or evening. Know the signs and symptoms of heat exhaustion and heat stroke,” forecasters wrote. “Wear light weight and loose fitting clothing when possible and drink plenty of water. Young children and pets should never be left unattended in vehicles under any circumstances. This is especially true during warm or hot weather when car interiors can reach lethal temperatures in a matter of minutes.”

Emily Sweeney can be reached at esweeney@globe.com. Follow her on Twitter @emilysweeney.