The first day of fall begins on Tuesday, say meteorologists

Sick of summer heat? Fall starts Tuesday, according to meteorologists.

"Meteorological" fall (aka autumn) is defined as the months of September, October and November in the Northern Hemisphere (it's spring in the Southern Hemisphere).

Most people consider the first day of autumn to be the autumnal equinox, which this year is September 23, according to WeatherBug meteorologist Mark Hoekzema. This is because, astronomically, the sun will be directly overhead of the equator as the Earth`s tilt begins to point the Northern Hemisphere away from the sun.

So astronomical fall is still more than three weeks away. People often say the "official" start of the seasons are the astronomical dates.

Meteorologists and climatologists need specific dates for the four seasons, so it makes sense for the seasons to follow our familiar monthly schedule. Scientists require set time periods to calculate averages and do year-to-year and decade-to-decade seasonal comparisons, Hoekzema said.

Thus, the three hottest months of June, July and August constitute summer, while the three coldest months of December, January and February are winter.

As for fall, September is more of a "fall-ish" month, while December is more wintry, so the meteorologists seem to have it right.

Unfortunately for those longing for crisp, cool fall weather, it'll be hard to find on Tuesday. Temperatures will be warmer than average for much of the country, which will be accompanied by stifling humidity.

The one cool spot will be the Pacific Northwest coast, where rain and temperatures in the 60s and 70s are forecast, according to the National Weather Service.