The Alabama Climate Report

Brought to you by the Office of the Alabama
Climatologist

Volume 10, Number 6 - September 2019

No one will argue the point that September 2019 was hot … very hot (and dry – indeed the driest!).  It was so hot I went back to the record books to see how this month compared with Septembers all the way back into the late 19th century.  As it turns out, by a few measures, this was the hottest of our last 125 Septembers, but overall, not the hottest.  In a relatively rare occurrence, September 2019 was the hottest month of the year, beating out the three summer months of June, July and August.  Depending on where you are in Alabama, this has happened about three or four times before.

Back to the record books.  The signature year for September heat was 1925 when the state suffered through heat that included the highest temperature every recorded in the state at Centerville, 112°F.  This month the top temperature was 105°F recorded at a station often found to be the hottest, Andalusia.  The average statewide temperature in September 1925 was 83.1° so that September 2019 came in third at 80.2 °F.  1921 was hot too at 80.9 °F.

If we focus on just the average of the daily high temperatures, this month was the hottest ever recorded in many places in the southern portion of the state like Montgomery (97.0°F), Selma (97.0 °F), Mobile (94.3 °F) with Tuscaloosa tying 1925 at 95.5 °F.  The official values from NOAA for the state indicate 2019 was the 2nd hottest in terms of daily high temperatures (93.4 °F) well behind the scorcher of 1925 at 96.8 °F.  What was particularly miserable was the stretch of days above 90°F with stations like Muscle Shoals (see below) and Montgomery hitting at least 90°F on every day this month.

Because it was so dry this month, the nighttime temperatures fell to levels a little lower than those in 1925, so that the average temperature (average of daily highs and lows) in the stations mentioned above was warmer in 1925 than 2019.  The more northern stations were cooler than 1925 in both daily highs and daily average temperatures.

To say it was “dry” is an understatement.  NOAA reports this month’s statewide total of 0.45 inches was so low that it garnered the award for driest in the 125 years for which we have records.  This value is a paltry 12% of the normal of 3.78 inches.  Several stations reported zero for the month (which has happened on rare occasions in the past.)

There was a downpour in the Mobile area on the 19th that dropped over 3 inches to boost totals there, and a couple of storms over and east of downtown Huntsville on the 10th and 11th left enough to push a few monthly totals over 1.5 inches. But the statewide average was less than half an inch.

One concern that is often swept under the rug in reports of extremes today is the use of weather stations, often airport stations, that have experienced the effects of city-growth for climate comparisons.  By some measures, these stations tend to be a bit warmer than the rural areas in which most of our weather records were derived, especially in the pre-WWII era before being moved to the airports (around which cities tend to expand).  So comparing an airport station today with a rural station from 1925 may not give the best information. 

During 2007 to 2009 my office installed 15 high-quality, well-cited weather stations around the state to avoid the warming influence of general urban development around the traditional weather stations.  For September 2019, I compared the average daily high temperature between a subset of my stations that were near those which are commonly used for weather observations (Clanton, Greensboro, Mobile, Montgomery, Muscle Shoals, Scottsboro, Talladega, Troy, Tuscaloosa.) In every case, my stations reported cooler September temperatures than those at neighboring official stations.

In another case, the airport station in Muscle Shoals recorded temperatures exceeding 90°F on every day in September – the first time that has happened since records began in 1893.  But across town at my climate weather station, there were 12 days in the month that did not exceed 90°F.  So, you can see we have some discrepancy issues with our surface data.  These kinds of results support the claim that today’s weather reports often have a bit of non-climate warming due to city growth.  On the other hand, this also indicates that since most people live in cities, they really are experiencing hotter and hotter temperatures through the years.

Be that as it may, even with a little boost of heat from city growth around the weather stations, September 1925 was warmer in Alabama than 2019.  Can you imagine what it was like in 1925?  Hotter and without air conditioning – think about that.  All I can say is God Bless Alabama Power, PowerSouth, TVA and all the others who send electricity into our homes to make our personal climate so much better.

- John Christy
The Alabama State Climatologist