August has arrived. What kind of weather do we normally expect in the Tennessee Valley?
Today marks the arrival of August. We are on the downhill slope of not only the year, but summer as well. Meteorological summer goes through the end of August, and astronomical summer ends later in September.
So, what exactly can we normally expect from the weather across the Tennessee Valley during August? It turns out, statistically speaking, what we expect in an average July carries through August as well. Our average monthly high temperature is 91 degrees, with an average monthly low of 69 degrees. Our high temperature averages in the lower 90s right through until the end of the month, when statistically speaking, we finally see it slide back down into the upper 80s as we get ready to head into September. We can definitely get much hotter than our "averages" though, and August is one of the months when we are most likely to get into the triple digits if we are going to. Our record high for the month is 108 degrees, set back in 1930. It's surprising to see, but we can occasionally have bouts of cooler air too. This is most noticeable at night when the infrequent drier air moves into the area and overnight temperatures cool. Our record low for the month in our area is 47 degrees! That record was set back in 1917.
You wouldn't know it without actually looking at the statistics because of the summer pop-up storms and the occasional tropical systems we have, but historically speaking, August is also our recorded driest month on average in the Tennessee Valley. Our "normal" rainfall total for the month of August is 3.15". October comes in second driest on average with 3.43", and September in third place with 3.72". All the other months of the year normally average over four inches of measurable precipitation. That certainly doesn't mean we can't have wet Augusts or Augusts with flooding events even, but this is a long term look at recorded averages that date back over the last 30 years or so. Our record maximum rainfall for the month is 10.60 inches, set back in 1894, and the record minimum rainfall for August was only 0.15 inches, which happened in 1990.
When it comes to any severe weather threats across the Tennessee Valley in the month of August, they are still present in a few ways. We can still see the complexes of thunderstorms that have the potential to produce damaging straight-line winds. Some of these are occasionally long-tracking and intense enough to be formally classified as derecho events. If one of these complexes develop the day before off to our northwest and develop a mesoscale area of low pressure that remains after the storms die off, that low pressure can sometimes approach our area the next day and give enough wind shear for the rare but not completely unheard of tornado threat in August. You're much more likely to see that happen earlier in summer, but it can happen this deep into the warmer months. In addition, our pop-up summer storms on a hot, humid afternoon can and do sometimes grow strong enough to produce damaging straight-line winds and occasionally even hail (much less frequent). Aside from these scenarios, we also run the risk of low-topped mini supercells carrying a tornado risk (usually EF0-EF2, but we have an occasional EF3 on record as well) in association with the remnants of landfalling tropical storms and hurricanes.
Speaking of the tropics, August also marks our begin into the peak of the Atlantic hurricane season. Historically, August is when we begin ramping up toward the peak of the season on September 10th. Our number of tropical storms and hurricanes significantly shoot up as we head through the month. Our chances of a hurricane obtaining major status (Category 3+) also significantly increase. Some of our most impactful hurricanes in history, such as Katrina, Andrew, Camille, and the Galveston hurricane of 1900, have formed in the month of August (the Galveston hurricane formed late month and made landfall in Texas in September of that year). August is when we enter the Cape Verde season, when tropical waves rolling off the west coast of Africa have a higher chance of developing into organized tropical systems and making their long tracks across the Atlantic basin. While some of these recurve harmlessly out to sea, a good number of them don't... either tracking through the Caribbean toward the Gulf of Mexico or toward the Bahamas and the Atlantic side of the United States.