August 2021 winds down tonight, as Wednesday is the 1st of September. August is actually usually one of our drier months across the Tennessee Valley, but this August has been rather wet. The climate reporting station at the Northwest Alabama Regional Airport in Muscle Shoals has recorded 9.21 inches of rain for the month (and there is a chance for that to tick up a few 0.01's before midnight as showers from Ida's remnants gradually exit the area). That's almost 5 1/2 inches above what is considered normal for our area.
September brings a new month, but also brings with it new weather stats. So, what can we "normally" expect the weather to be like during an "average" September in the Tennessee Valley area? The short answer is continued warm and continued dry. However, we know it's much more complicated than that. September is the first day of meteorological fall, but the autumnal equinox doesn't happen until September 22nd. That is the first day of astronomical fall ("official" fall). Generally speaking though, for the month overall, our average daytime high is in the mid 80s, with our overnight low in the mid 60s.
However, you can tell by looking at more detailed stats for daytime highs through meteorological fall here, it's not instantly cooler at the beginning of the month. The average daytime high to start the month of September is only down to 89 degrees. That's only a single degree lower than our average expected high in July and August! We still have very warm weather this time of year. The record high for the month of September in our area was 108 degrees, set in 1925, and we've actually occasionally had 100 degree temperatures into October! On the flip side, we can start getting chilly in September as cold fronts start to bring cooler air down. That is especially true for overnight temperatures. Our monthly record low for September was 36 degrees, set back in 1901.
As mentioned earlier, September is normally a dry month, with our average rainfall being about 3.72 inches. That is because our heavier rain events typically are associated with the occasional landfalling tropical system that directly affects the immediate area. We otherwise have to rely on isolated pop-up thunderstorms, which are very random in nature, and aren't as common in September as they are late spring and through the heart of summer. However, the weather doesn't always behave by "averages", and those long term averages are often a set of extremes smeared out over time. The weather will do what the weather does, and we certainly can have synoptic and mesoscale weather systems that bring us heavy rain events, just like we can at any time of the year.
September marks the peak of the Atlantic hurricane season, with September 10th being the absolute peak. As we have already seen, tropical systems CAN AND DO affect our weather directly here in the Tennessee Valley, even though we are far removed from the coastline. Landfalling tropical systems that impact our area can bring flooding rains, damaging wind gusts, and tornadoes. As the maps above with the typical formation zones and climatological tracks show, September is a likely time for systems to form in the Caribbean and Gulf of Mexico and then track northward toward the northern Gulf Coast. Late August and September are also the most likely times for there to be a landfalling major hurricane (Category 3 or higher), especially on the northern Gulf Coast.
If there is any good news, it is that September is in a relative "down time" for our area in relation to tornadoes. We do still have tornadoes in September. However, they are most often associated with landfalling tropical systems, which CAN AND DO directly affect our area, but not every single year. Once we approach October, and especially November and into winter, we begin moving into the time when we start watching storm systems embedded within the main jet stream for severe weather threats. However, the weather will do what the weather is going to do, and it doesn't always play by the rules. Very occasionally, we CAN get tornadoes here outside of tropical systems, just not too often. Aside from that, we do still get severe thunderstorms with damaging wind concerns this time of year in much the same way we do in the heart of summer.