Could Isaac Help the Illinois Drought?

As of noon on Monday, August 27, the track of Hurricane Isaac could pass through Illinois on Saturday (first map). Of course, it won’t be a hurricane – just a tropical depression. Even so, large rainfall amounts are expected to fall in parts of Illinois and Missouri (second map).

Back in 2008, I wrote about the impact of Hurricanes Ike and Gustav as the remains of those two systems dumped an impressive amount of rainfall across Illinois.

Perhaps a better comparison is with the drought of 2005. Like this year, Illinois was faced with a severe drought. However, the remains of four tropical systems brought needed rainfall into the region, especially southern Illinois (third map). The four tropical systems were Tropical Storm Arlene in June, Hurricane Dennis in July, Hurricane Katrina in August, and Hurricane Rita in September. In fact, the total rainfall from these four systems ranged from almost 8 inches in southern Illinois to about an inch in northern Illinois (fourth map). You can read more about the impact of tropical storms in 2005 in this article and this report (starting page 47).

Five day track forecast from the NWS issued Monday at noon, CDT. Click to enlarge.
Five day potential precipitation map, ending Saturday morning, from the NWS. Click to enlarge.
Tropical storm tracks in 2005 for Arlene, Dennis, Katrina, and Rita. Source: Illinois State Climatologist. Click to enlarge.
Precipitation contribution from four tropical systems that passed through Illinois in the 2005 growing season – Arlene, Dennis, Katrina, and Rita. Source: Illinois State Climatologist. Click to enlarge.
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Tropical Storm Hermine Reaches Illinois

The remains of Tropical Storm Hermine have reached Illinois this morning. Rainfall amounts of 1 to 3 inches are possible and flash flood warnings have been issued. Check the National Weather Service as this event unfolds.

While we don’t often use the words “tropical” and “Illinois” in the same sentence, the remains of tropical storms and hurricanes have reached us before. Most of these systems came on shore in Texas and Louisiana and weakened considerably as they moved northward. Usually, the severe weather is gone by the time they reach Illinois but they can produce large amounts of rain than can lead to flooding.

The passage of four tropical systems alleviated drought impacts, particularly in southern and central Illinois during the 2005 growing season. The four systems were Tropical Storm Arlene, and Hurricanes Dennis, Katrina, and Rita. An article in the Illinois State Academy of Science by me described that situation in more detail.

More recently, in September 2008 the remains of Hurricanes Ike and Gustav produced heavy rains and flooding in Illinois. More on that particular situation can be found on my website.