Many people consider the autumnal equinox on Sunday as the official end of summer and the first day of fall. If you were waiting on the autumnal equinox for fall weather, though, you may have to keep waiting.
On the equinox, the Earth's axis is tilted neither toward nor away from the sun, resulting in a nearly equal amount of daylight and darkness at all latitudes, according to the National Weather Service. The day of the equinox can change from year to year because the time it takes for Earth to orbit the sun is slightly longer than our Gregorian calendar year. Thus, the autumn equinox can occur on the calendar between Sept. 21 and Sept. 24.
The autumnal equinox is not a day, per se, but instead is a moment in time that happens simultaneously across the Northern Hemisphere. This year it happens at 7:43 a.m. Sunday for those of us living in the Central time zone.
Normally, late September is when foliage begins to change color and the average daily temperature starts to drop from summertime levels in many areas in the Northern Hemisphere.
The equinox has no relationship to Houston's weather, and "fall" temperatures in Southeast Texas typically don't begin until late October. According to temperature data going back to 1889, the average maximum temperature for Sept. 22 in Houston is 87.5 degrees and the average minimum temperature is 68.9.
Houston's climate after the autumnal equinox isn't guaranteed to bring cooler or even warmer temperatures, either. The highest temperature recorded on Sept. 22 was 100 degrees in 2005, and the lowest minimum temperature recorded was 49 in 1983.
Sunday, the day of this year's fall equinox, should be a hot one with a forecast high temperature of 91 degrees, which with humidity will feel more like 99.
Sept. 22 is in the middle of peak Atlantic hurricane season, when the development of storms and hurricanes in the tropics is most likely to occur.
Although the fall equinox is not responsible for hurricanes, the Houston region is well aware of the possibility of a hurricane hitting on Sept. 22, as was the case in 2005 with Hurricane Rita.
On that day, one of the largest evacuations in U.S. history unfolded as Galveston, Houston and College Station each set daily record-high temperatures. As many as 49 people died, not by the hurricane, but mostly because of heat exhaustion and the evacuation of elderly residents. More died in the evacuation for Hurricane Rita than from the storm itself, according to the National Weather Service.