Long Island weather: Heat advisory extended through Friday for all of LI

The National Weather Service has expanded and extended its heat advisory to all of Long Island and the region through 8 p.m. Friday, as the heat index is predicted to soar near 100 degrees.

The weather service also extended an air quality alert for the region to Friday, effective 11 a.m. to 11 p.m.

"One more hot and humid day is forecast on Friday with forecast heat indexes reaching the mid to upper 90s with isolated areas getting to near 100," the weather service said in a Thursday night briefing. "Heat advisory is in effect for our entire forecast region until 8PM Friday."

Thursday was another scorcher and the second of three days of dangerously hot weather.

Temperatures hit the low 90s Thursday but with humidity, the heat index was between 95 or 100 — and possibly to 105 in "isolated" spots, the weather Service said.

A heat advisory was originally to run through 8 p.m. Thursday for Nassau and northwest Suffolk but the weather service extended and expanded it, along with the air quality alert, on Thursday.

A backdoor cold front on Friday — which means it swings in from the east, the opposite of the usual direction — will usher in cooler weather in the form of storms Friday night and into Saturday.

"There will be a greater chance of showers and thunderstorms Friday afternoon into Friday night with more showers forecast for the start of this weekend," the weather service said.

Then, finally, relief.

Saturday, daytime highs will drop into the 70s and stay in the 70s and low 80s through Wednesday. Showers will be possible almost every day.

The recent heat can be blamed on a high pressure system sitting off the mid-Atlantic coast that is "bringing in a more humid air mass," the weather service explained.

With Joan Gralla