Frequency Of Tornadoes From Remnants Of Tropical Systems

Yesterday was the 6 year anniversary of Tropical Storm Arlene's passage (or at least its remnants) through Indiana.  While these events can bring us heavy rain from time to time, they are usually fairly forgettable.  However, Arlene is a bit of a stand out because it produced 2 tornadoes south of Indianapolis.  That got me thinking - how often do tropical remnants produce tornadoes here?

In an attempt to answer that question, I scanned the National Hurricane Center's records since 1950 (since that is about the time that tornado record keeping began to improve).  It was assumed that a remnant tropical system would've at least needed to reach the latitude of Kentucky to have a substantial chance of producing a tornado in Indiana.  I found 23 such systems which I am not going to list here.  I then chose to narrow the criteria to systems in which the remnant circulation passed through Illinois or Indiana, thus achieving greater latitude and putting us along or east of the track.  I found 14 of those systems and they are listed below:


1960 Tropical Storm #1
1961 Hurricane Carla
1965 Hurricane Betsy
1968 Tropical Storm Cindy
1979 Hurricane Bob
1979 Tropical Storm Claudette
1988 Hurricane Gilbert
1995 Hurricane Erin
2005 Tropical Storm Arlene
2005 Hurricane Dennis
2005 Hurricane Katrina
2005 Hurricane Rita
2008 Hurricane Gustav
2008 Hurricane Ike


In order to determine whether these tropical events produced any tornadoes in our area, I examined tornado records to coincide with the general timeframe that the remnant circulation passed through the area.  In a few cases, tornadoes occurred 1 or 2 days after the remnants passed and it was determined that those tornadoes were caused by a different weather system.  Out of the 14 storms listed above, I can only find 2 storms which were undoubtedly directly responsible for tornado production in the state - Tropical Storm Arlene in 2005 and Hurricane Gustav in 2008.  As previously stated, the remnants of Arlene produced 2 tornadoes, while the remnants of Gustav generated a tornado in Jasper county.

A potential third tornado case is Hurricane Gilbert in 1988.  The remnants of Gilbert moved northeastward through Missouri and Illinois, apparently in association with a significant trough/low pressure system in the Midwest.  5 tornadoes occurred in central and southern Indiana, but it is unclear if these tornadoes were directly caused by Gilbert or the larger weather system.

I have drawn the approximate tracks of Gilbert, Arlene, and Gustav below.    

So, to answer the question of how frequent these types of tornadoes are...not very frequent.  Depending on whether one includes Gilbert, there are either 3 or 8 tornadoes and either figure computes to well less than 1% of Indiana's tornadoes occurring from the remnants of tropical systems.  It is possible if not probable that these events have been underreported to some extent, but the same is probably true for other tornadoes which means that the percentages wouldn't change much.