Allison, an early-season tropical storm developed from a tropical wave in the Gulf of Mexico during the first week of June 2001. It made first landfall south of Houston, Texas late on the 5th as a strong tropical storm. Over the next four days it delivered heavy rain that extended eastward to Alabama when a front stalled over the Gulf Coast states. Late on the 9th Allison moved southeastward back over the Gulf near the first point of landfall with its circulation weakened but still intact. Over the water, the surface circulation remained weak. Early on the 11th, Allison made second landfall on the coast of Louisiana. After it tracked inland, an eye-like feature became evident. Doppler velocity indicated wind speeds of over 25ms^-1 south of this eye-like feature. Infrared images showed increasing upper-level outflow associated with a subtropical jet. Surface stations at sea level fell suggested that the central pressure slightly from around 1003hPa at landfall to about 999hPa in southern Mississippi.

It is postulated that highly saturated ground conditions from the antecedent heavy rain over eastern Louisiana combined with overrunning from the stalled front plus favorable upper level outflow associated with the subtropical jet, contributed to the inland intensification of the circulation. In this paper, observations showing the inland intensification will be presented and compared with numerical simulation results for the intensification period using the Penn State/NCAR MM5 modeling system.