An examination of the evolution of precipitation-enhancing mesoscale features associated with a landfalling tropical cyclone

Landfalling tropical cyclones (TCs) provide a challenging forecast scenario because of their potential to cause heavy rainfall both near and far from the storm center. For landfalling TCs, the primary cause of precipitation near the cyclone center is ascent associated with the TC's circulation, while distant rainfall totals are often significantly augmented by locally forced mesoscale features. These mesoscale phenomena, which include coastal fronts, orographic enhancement, and cold air damming, are directly influenced by land/sea thermal boundaries and/or significant terrain variations. This presentation will focus on the temporal and spatial evolution of coastal fronts and cold air damming events which are induced or enhanced by the presence of a nearby tropical cyclone and lead to especially large rainfall totals.

Atlantic Tropical Storm Marco (1990) was chosen for intensive study because two distinct instances of coastal frontogenesis, cold air damming, and orographic enhancement significantly affect the final precipitation distribution. Marco was a major contributor to the more than 500 mm of precipitation which fell in parts of Georgia and South Carolina; however, much of the heavy rainfall in these regions occurred distant from Marco in a region of coastal frontogenesis and convection. An overview of the synoptic and mesoscale setup surrounding Marco and the heavy inland precipitation will highlight the importance of the two coastal fronts and cold air damming in the overall rainfall pattern. Then, a thorough examination of the evolution of these mesoscale phenomena will be presented through various kinematic and dynamic diagnostics in both surface and near-surface fields. Finally, these results will be amalgamated to show how the presence of Marco led to a strengthening of the inland coastal fronts and cold-air damming, which thus increased precipitation totals distant from the storm center.