Portland’s July Fourth holiday heat wave starts Thursday with a relatively mild high in the low 90s, but then the fireworks really get going with an excessive heat warning kicking in until late Sunday.

The National Weather Service predicts “dangerously hot conditions,” including a string days at 100 or over and warm nights cooling only into the mid-60s and low 70s. Fire danger also picks up as the heat dries out vegetation, forecasters say.

The hottest day is expected to be Sunday at 104 .

The excessive heat warning runs from noon Thursday until 11 p.m. Sunday. No rain is expected at least through the middle of next week.

Here’s the rundown:

Thursday: Sun, a high of 91, winds up to 10 mph and an overnight low around 65.

Friday: Sun, a high near 100, winds up to 10 mph and an overnight low around 69.

Saturday: Sun, a high near 102, winds up to 5 mph, an overnight now around 71.

Sunday: Sun, a high near 104 and an overnight low around 69.

The heat continues into the week with 101 predicted for Monday, 99 on Tuesday and 90 Wednesday.

One place for relief if you can get there: The Oregon coast will stay mostly in the 70s and 80s during the day through the hot spell, but weather service meteorologists say the relief will extend only a few miles inland.

-- Margaret Haberman; mhaberman@oregonian.com; 503-221-8375