U.S. Tornadoes: The Month of September by the Numbers

There’s little doubt as we get into September that the off season for tornadoes is upon us. The month is the 7th most active all-time, but the month tends to be somewhat hit or miss, with bigger months and lower months intermixed throughout the record.

While tornadic activity in September is comparable in overall numbers to that in the transition to spring, there is still some “warm season memory,” meaning more territory than coming out of the cold season is at play for tornadoes during the month.

September Tornado Climatology (1950-2011)

Total tornadoes: 3,004 (-921 from August)
Climatological average (1991-2010): 73.9 (-9.3 from August)
10-year average (2002-2011): 88.4
10-year median (2002-2011): 59
Long-term average (1950-2011): 48.5
Monthly high: 295 (2004)
Monthly low: 1 (1952) / 8 (2009), lowest recent
Total fatalities: 125
Total injuries: 2,848

Raw tornado counts by day continue their decline, and the low range from day to day seen in earlier summer month shows signs of growing — highlighting the importance of outbreaks toward overall counts in September. While September has considerably fewer overall tornadoes compared to March, over half of September days see a tornado touchdown in the U.S. on (1991-2010) average compared to less than 40% in March.

As with many months, the states of Texas and Florida lead the pack. This is primarily due to Texas’ size and Florida’s proclivity for air mass tornadoes (waterspouts moving ashore, landspouts, etc.). Tropical activity also adds to these counts, but more often than not, it’s at the margins. Other southern states, including Louisiana and Mississippi likely rise several spots thanks to tornadic activity from landfalling tropical systems, as we’ve examined in northern Gulf of Mexico systems and with Isaac specifically.

Significant tornadoes (or those F2/EF-2+) made up 16.2% of all September tornadoes during the period in the United States, but they caused 85.3% of the deaths. The deadliest September tornado is an F3 that hit the town of Crozet in Albemarle County, Virginia. This tornado, spawned by the remnants of Hurricane Gracie, killed 11 people and was one of numerous tornadoes that day.

Related: September Tornado Climatology (TornadoTitans.com – Plains focus)

U.S. Tornado Climatology by Month

All: Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
Significant: Jan | Feb | Mar | Apr| May | Jun | Jul | Aug | Sep | Oct | Nov | Dec

SPC tornado data obtained at the Tornado History Project. Images can be selected for larger versions. Get updates about U.S. Tornadoes on Twitter and Facebook. Official 2012 data will be available during spring 2013.