We’ve made it into the first few days of September. That also means we’ve slipped our way into meteorological fall. While astronomical fall this year will be Monday, September 22nd, meteorological fall begins at the start of the month simply for making it easier to keep up with weather records and climatology. As you would expect, September is a month of transition here in the Tennessee Valley. Our average daytime high for the month is 86 degrees, but that starts at almost 90 at the beginning on the month and then comes in shy of 80 as we head out of September into the beginning of October. Our average overnight monthly 63 degrees, but that begins at 68 at the start of the month and is down to 58 as we end the month. September is no stranger to either hot or chilly weather. Using records from the Northwest Alabama Regional Airport in Muscle Shoals (our region’s main official NWS climate record site), that reporting station has been as hot as 108 in September 1925 and as chilly overnight as 36 back in September 1901. September and October are two of our driest months, based on long-term averages. September in particular only averages just over 3 and a half inches of precipitation. Historically, a large part of what rain we do get during September can often come from landfalling tropical systems, but we can and do start to see cold fronts come down this time of year… and just like has been the case this year, they can sometimes bring rounds of heavy showers and thunderstorms.
In terms of severe storms, September usually isn’t a very active month. We can occasionally see the summer type pulse thunderstorms that can produce downbursts of damaging winds. We can also occasionally see a cold front bring a line or cluster of storms with damaging winds. In terms of tornadoes, September doesn’t see a lot here. With the exception of a rare early season cold front and upper-level system with enough wind shear for a tornado threat (September 2006 comes to mind), just about the only way you will see a tornado threat this time of year in the Tennessee Valley is with a landfalling tropical system. These tornadoes are typically short-lived, fast-moving, and don’t do extreme damage… but they are still a threat when they do sometimes occur.
Speaking of tropical systems, September is historically the most active month for tropical storms and hurricanes in the Atlantic basin. The climatological peak of the Atlantic hurricane season falls on September 10th. While a lot of storms in September either recurve in the open Atlantic or target the East Coast, we also get our fair share of tropical storms and hurricanes in the Caribbean and Gulf. Major hurricanes (Category 3 and higher) making landfall on the northern Gulf Coast are a significant threat in the month of September during those years when the Gulf is active. These systems do affect our area after landfall as well. The remnants of tropical systems making landfall on the northern Gulf Coast often move northward into our area, bringing heavy rain and flooding, damaging winds, and spin-up tornadoes.
