Abstract

After looping through east Texas and flooding the Houston metropolitan area with as much as 36" of rain over 4 days, Tropical Storm Allison moved back over the Gulf of Mexico, only to make landfall again over southern Louisiana. This second of three cases on this storm examines the predictability of its behavior over the southeastern United States, as Allison moved steadily east-northeastward from the Louisiana coast over the course of 3 days, before stalling over eastern North Carolina.

This portion of the storm's history was remarkable for:

• Maintenance of storm circulation
• Maintenance of some aspects of its tropical characteristics
• Inability of the mesoscale models at NCEP (both Eta-22 and 10-km nests) to capture the behavior of the storm

This case examines the behavior of the Eta model in forecasting the movement and precipitation from Allison as it moved through the Southeast.

Learning objectives

While going through the case study, consider these questions:

1. What does increased horizontal resolution "buy us" in prediction of movement and/or strength of systems like Allison?
   
2. How do precipitation schemes (both large-scale and convective) potentially affect the quality of the model forecast?
   
3. How might problems with the initial conditions have played a role in the forecast for Allison?
   

Credits

Stephen Jascourt for helpful discussions
Ying Lin for radar rainfall estimates
Eric Rogers for help with obtaining Eta-22 and Eta-10 model data

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