Feature

Flooding Rains in U.S. Southeast Like Those of a Tropical Storm
09.23.09
 
September 23, 2009

Totals for the 8-day period from September 14 to 22, 2009. > View larger image
The TRMM-based, near-real time TMPA rainfall totals for the 8-day period from September 14 to 22, 2009 show the highest rainfall amounts in central Tennessee, central Alabama, north central Mississippi, and north central Georgia, around the Atlanta metropolitan area.
Image Credit:SSAI/NASA, Hal Pierce
Flooding Rains in U.S. Southeast Like Those of a Tropical Storm

So far at least 9 people are dead and others are missing across the southeastern United States as a result of severe flooding brought about by several days worth of heavy showers and thundershowers. Normally at this time of year, slow moving or stalled out tropical storms or hurricanes bring the amounts of rainfall and flooding seen in this week's event, but not this time.

Atlanta, Georgia was especially hard hit with reports of over 15 inches of rain in the metro region. The culprit was a persistent area of low pressure located over the lower Mississippi River Valley that pumped copious amounts of moisture up from the Gulf of Mexico northeastward over the Southeast, providing fuel and a trigger for the numerous showers and thundershowers. A stagnant upper-air pattern allowed the area of low pressure to persist for several days in the same location.

Armed with both a passive microwave sensor and a space-borne precipitation radar, the primary objective of the Tropical Rainfall Measuring Mission satellite (better known as TRMM) is to measure rainfall from space. For increased coverage, TRMM can be used to calibrate rainfall estimates from other additional satellites.

The TRMM-based, near-real time Multi-satellite Precipitation Analysis (TMPA) at the NASA Goddard Space Flight Center, Greenbelt, Md. is used to monitor rainfall over the global Tropics. TMPA rainfall totals for the 8-day period from September 14 to 22, 2009 for the southeastern U.S. and the surrounding region show the highest rainfall amounts in central Tennessee, central Alabama, north central Mississippi, and north central Georgia, around the Atlanta metropolitan area.

Nearly the entire southeastern U.S. from the Gulf Coast to the Ohio Valley and from the southern Mississippi Valley to the southern Appalachians received at least 50 mm of rain (~2 inches, medium green) with a good portion receiving at least 100 to 150 mm (4 to 6 inches, shown in light green and yellow areas, respectively). Embedded within these regions are locally higher amounts exceeding 250 to 300 mm of rain (~10 to 12 inches, shown in orange and red, respectively). The highest TMPA rainfall totals for the Atlanta region are on the order of 350 mm (~14 inches).

To see an animation of the calculated flood potential for this event, Updated Tuesday 23 September 2009, visit: http://trmm.gsfc.nasa.gov/trmm_rain/Events/usa_flood_potential_2009092306.mpg.

Heavy rain amounts (from satellites) and flood potential calculations (from a hydrological model) are updated every three hours globally with the results shown on the "Global Flood and Landslide Monitoring" at: http://trmm.gsfc.nasa.gov/publications_dir/potential_flood_hydro.html on the TRMM web site pages. TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Text Credit: Steve Lang, NASA/SSAI, Goddard Space Flight Center