Quick Facts:

	Ave	10Y	Low (year)	High (year)
HLA	82.15	82.43	76.83 (2020)	86.25 (2019)
Highs	101.1°F	101.3°F	98°F (2017, 2018)	109°F (2011)
Lows	60.46°F	60.60°F	52°F (2010)	73°F (2019)
Precip	3.03”	3.03”	0.04” (2015)	11.75” (2020)

 

 

September Temperatures

September’s 10-year temperature average is 82.43°F, our fourth-hottest month (behind August, July, and June) — September averages closer to all the top three months than it does to the next two (May and October). While September has never been warmer than the same year’s August, it does (rarely) beat June (2015, 2019, 2021) and once beat July (2019). September 2019 was the warmest September on record, averaging 86.25°F (beating 2015, which topped 2011). I couldn’t find when the coolest September was, but the coolest recent one was in 2020, dropping drastically from the previous year to 76.83°F.

According to a variety of sources I searched, the coldest temperature ever recorded in September was 42°F, on Sept. 24, 1994, while the warmest temperature September has ever seen was 110°F, on Sept. 1, 2000. During my 12 years of record keeping (2010-21), the coolest September day was Sept. 28, 2010, with a low of 52°F. The warmest was 109°F on Sept. 25, 2011. Only five daily record lows occurred during the past 12 years (most in 2011), while twelve daily record highs belong to the same period (also most from 2011).

September averages 3.1 hundred-degree days per year — days in which the high is 100°F or warmer — third of all months (behind August and July, and only barely ahead of June). In the past 12 years, September has ranged from zero such days (2017 and 2018) to 11 (2011). Once, in 2021, September had more 100-degree days than any other month, but only because July and August oddly had zero that year. As for ninety-degree days, September trails July, August, and June, with 20.9 such days each year. Most years, September sees 20 or more ninety-degree days. Three times, it beat June (2015, 2019, and 2021), and once it beat July (2021).

 

 

Precipitation

Rainfall in September varies more than any other month. It can be the wettest month of the year (11.75 inches in 2010) or the driest (0.14 inches in 2019). So far, the pattern seems to be a very dry year followed by three rainier ones. September averages 3.03 inches of rain, the third-wettest month (behind May and October).

September averages 6.8 days per month that exhibit precipitation — close to the average of all months.

Trends And Patterns

In the ten years I’ve been keeping track, September’s temperatures hovered fairly close to its average, until 2019 and 2020, which saw, respectively, a large increase and a large decrease — returning to normal in 2021. It does not match well with the yearly temperature averages or with other months. September’s rainfall and temperature track fairly closely with each other — our hottest Septembers are also our driest. However, September’s rainfall is not a good predictor of annual rainfall.

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