In this Aug. 15, 2003, file photo, Andrew Kelly, 15, plunges into the Mousam River to cool off from the heat in Springvale. Credit: Robert F. Bukaty / AP

The dog days of summer aren’t over yet, with this latest heat wave set to drive the heat index up to 100 degrees Fahrenheit across Maine.

Nearly all of Maine except for the Down East coast and the western border region has been placed under a heat advisory through Thursday evening.

The mercury is climbing into the 90s across much of the state, while the dew point is close to 70 percent. That paired with the ample sunshine will make for a sweltering combo, according to the National Weather Service office in Gray.

The heat will feel like nearly 100 degrees in Penobscot County from Bangor to Millinocket. In Aroostook County, it will feel like 97 degrees across a wide swath of country from Houlton to Presque Isle, while from Caribou to Madawaska it will feel like 93 to 95 degrees, the weather service’s Caribou office reported.

Coastal Hancock and Washington counties will feel a bit cooler with the heat index sitting in the mid-80s. But the Maine Department of Environmental Protection has warned of elevated ozone levels along the coast.

Meanwhile in southern Maine, Portland is forecast to see the heat index hit 101, while the midcoast from Belfast to Brunswick will see it range across the low to mid-90s, according to the weather service’s Gray office.

With those sweltering temperatures, weather officials urge Mainers to avoid strenuous outdoor activities, drink plenty of fluids and seek out a cool shelter if needed.

There is at least one place in Maine that will be spared the brunt of Thursday’s heat. Eastport’s heat index is forecast to top off about 69 degrees during the afternoon, according to the weather service’s Caribou office.

The heat will continue to dominate in Maine through the weekend, when temperatures should fall back within a normal range by Sunday.