NEW YORK: The autumnal equinox arrives September 22 at 8:05 p.m. ET, marking the official start of astronomical fall in the Northern Hemisphere.
At the equinox, the sun is positioned directly above Earth’s equator, resulting in nearly equal periods of daylight and darkness across much of the world.
The word “equinox” comes from Latin and means “equal night.” In the Southern Hemisphere, the September equinox marks the beginning of spring.
Two definitions of fall
Astronomers consider Sept. 22 the end of summer and the beginning of astronomical autumn. Meteorologists and climatologists, however, define fall as beginning Sept. 1, grouping the year into three-month seasons based on annual temperature patterns.
Under the meteorological calendar, summer runs from June through August.
El Niño may keep temperatures elevated
The arrival of fall does not necessarily mean an immediate drop in temperatures. El Niño, combined with the effects of climate change, is expected to contribute to warmer-than-normal conditions in parts of the Northern Hemisphere this fall.
Forecasters expect the current El Niño to strengthen later this fall and potentially rank among the strongest events on record.
August was the warmest month globally on record for combined land and ocean temperatures, while the contiguous United States experienced its warmest year-to-date period on record. Ten states, including Texas, California and Arizona, recorded their warmest starts to a calendar year.
Days will gradually become shorter
Following the equinox, daylight hours will continue to decrease across most of the Northern Hemisphere until the winter solstice.
Earth’s approximately 23.5-degree axial tilt causes the Northern Hemisphere to gradually turn away from the sun, resulting in shorter days and longer nights as winter approaches
