Even though school has started almost everywhere and the foliage is taking on autumnal hues, the weather is refusing to shift into fall mode.

The hot sticky temperatures which have been around for most of the past month may be around for most of September, Mike Kistner, a meteorologist with the National Weather Service in Gray, said Sunday.

Kistner said children headed back to un-airconditioned classrooms after the Labor Day weekend will not find any relief until the end of the week.

Temperatures on Labor Day will hit 90 inland in southern Maine and the upper 80s along the coast. Skies will be sunny and the air humid. The average high for Portland at this time of year is 74.

“It will definitely pretty much feel like the middle of summer,” Kistner said.

Low temperatures will be in the lower 60s Monday night. Tuesday will be a repeat of Monday, but the lows will struggle to drop below 70 degrees.

Kistner said a high ridge from the south is responsible for the weather. He said Wednesday may be a little cooler. A cold front will move in Thursday, which could trigger showers and thunderstorms. Normal temperatures will return Friday.

Kistner said it is anyone’s guess whether the warm pattern will reappear. He said the service’s Climate Prediction Center is calling for above-normal temperatures through Sept. 20.