For Long Island, the heat wave starts today with temps around 90 degrees. Temps will always be lower on the south shore and east end. Low 90's tomorrow and mid 90's Sunday with increased humidity creating a heat index of 100 to 105 degrees. Low 90's Monday and then upper 80's for the rest of next week. It will be humid all week next week with dew points mostly in the low 70's. There will be more clouds around for the 4th of July and can't rule out a couple of scattered showers. It looks like a cold front will be approaching next Saturday with clouds and showers/thunderstorms possibly by late afternoon, but it's 8 days away! The image below is the National Weather Service model blend. I think the temps are pretty accurate, but you can add a couple of degrees for the normally hotter areas, especially NW Nassau.
Image from weathermodels.com