Eyewall evolution of Hurricane Katrina near landfall using NEXRAD reflectivity and radial velocity data

Hurricane intensity variation at landfall represents a crucial yet difficult forecast problem. On 29 August 2005, at 1310 UTC, Hurricane Katrina made landfall along the Central Gulf Coast near Buras-Triumph, Louisiana as a strong Category 4 (on Saffir-Simpson scale) hurricane with maximum sustained winds of 70 m/s and a central pressure of 918 mb. Fluctuations in eyewall structure were observed as Katrina approached the coast. At landfall, the eyewall quickly filled in and the storm's overall intensity decayed rapidly, losing hurricane-strength 160 km inland, near Jackson, Mississippi.

NEXRAD radar observations captured in detail Katrina's evolution before and during landfall. This study examines the evolution of the eyewall region of Hurricane Katrina as the system made landfall, using NEXRAD radar data from Lake Charles, Louisiana between 1000 UTC 29 August to 1400 UTC, before the Lake Charles radar went offline. NEXRAD level-II reflectivity and radial velocity data (five minute time interval) were analyzed using NCAR's SOLO radar analysis software, for the four hours prior to and during landfall.

A comparison of the eye's translational speed with the maximum inbound vs. outbound radial velocity in the eyewall revealed rapid changes in the eyewall windspeed as the storm approached the coast. The motion and echo top height of convective elements within the eyewall are placed in the context of the eyewall velocity fluctuations.

Observations further suggest a significant decrease in the translational speed of Katrina's eye as the storm approached land, as well as a significant decay of maximum surface wind speeds as the system progressed inland. An observed slight increase in maximum surface wind speeds moments after landfall, suggests that surface friction had immediate impacts on Katrina at landfall.