The overland reintensification of Hurricane Danny in July of 1997

The only landfalling tropical cyclone of the 1997 Atlantic hurricane season, Hurricane Danny came ashore near Mobile, Alabama on 18 July as a minimal category one hurricane on the Saffir-Simpson Scale. After traversing the southeastern United States over the next three days the storm began to re-intensify as a tropical cyclone while over land in Virginia and North Carolina. The fact that Danny was in close proximity to a lower tropospheric frontal zone when it began to re-intensify suggests the importance of lower tropospheric baroclinicity in the redevelopment of the tropical cyclone.

This study uses observations including surface, upper-air, radar, and satellite data along with numerical model simulations employing the NCAR/PSU MM5 mesoscale model to diagnose the spin-up of the lower tropospheric vortex.

Results will show that Danny reintensified due to an interaction with a lower tropospheric thermal boundary over Virginia. In addition, the upper-tropospheric synoptic scale flow was found to be favorable for development of a low-level cyclone. Notably, an upper jet located to the northeast of the storm was established to be an outflow jet for the developing low-level disturbance enhancing upward vertical motions in the center of the cyclone. Danny displayed characteristics of a tropical cyclone including a troposphere-deep warm core during the reintensification phase.