The term 'tropical' refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe, and their formation in maritime tropical air masses. The term 'cyclone' refers to such storms' cyclonic nature, with anticlockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere. Depending on its location and intensity, a tropical cyclone can be referred to by names such as 'hurricane', 'typhoon', 'tropical storm', 'cyclonic storm', 'tropical depression', or simply 'cyclone'.
The storm dropped heavy rainfall along its path, peaking at over 40 inches (1000 mm) in Texas. The worst of the flooding occurred in Houston, where nearly $5 billion (2001 USD) in damage occurred. There, 30,000 became homeless after the flooding destroyed 2,744 homes. 23 people died in Texas.
Throughout its entire path, Allison caused $5.5 billion (2001 USD) in damage and 41 deaths. Aside from Texas, the places worst hit were Louisiana and southeastern Pennsylvania. Allison is the only tropical storm to have its name retired without ever reaching hurricane strength.
Tropical Storm Allison over Mississippi as a Subtropical Storm on June 11, 2001. Despite the eye feature, Allison only has winds of 45 mph. The picture is a radar reflectivity image from Mobile, Alabama.