Mainers should prepare Thursday for a day that rivals a summer scorcher, with forecasters predicting record-setting heat in Portland and unhealthy ozone levels for the entire coastline.

The Maine Department of Environmental Protection also issued an air- quality alert for Thursday, warning people with respiratory problems to limit strenuous outdoor activity.

Eric Sinsabaugh, a meteorologist with the National Weather Service in Gray, said he expects Portland to shatter a heat record set 68 years ago.

“We will crush that record,” Sinsabaugh predicted, referring to the record high of 82 degrees set in Portland in 1949. Sinsabaugh is forecasting a high of 93 degrees in Portland on Thursday. “The good news is that while it will be very hot, the humidity should be fairly low.”

Sinsabaugh said a “huge, sprawling ridge of high pressure that’s affecting the entire East Coast,” will produce the extreme heat.

The DEP said the air-quality alert will begin at 11 a.m. and remain in effect through 11 p.m. The most vulnerable individuals when ozone levels are elevated are the very young, elderly and people with respiratory conditions such as asthma or bronchitis.

Martha Webster, an air-quality meteorologist with the Maine DEP, said it’s not too early in the season for the state to be concerned about poor air quality. An ozone alert was issued April 11 by the DEP for the area around Cadillac Mountain in Acadia National Park.

“It’s not unheard of, but it’s not often that we have ozone levels this high so early in the year,” Webster said.

Webster said ozone levels started to build on Wednesdsay and will peak Thursday, with unhealthy levels of ground level ozone affecting the entire coast. The air quality alert extends 15 miles inland, she added.

Ozone levels are higher during the afternoon and evening while particulate pollution levels tend to be higher in the morning and evening, according to the Maine DEP. Ozone can reach high levels from late March through the end of September.

By Friday, the heat and poor air quality should subside, leaving most of the state to enjoy a mostly sunny day with highs in the 70s.

Dennis Hoey can be contacted at 791-6365 or at:

[email protected]