Precipitation enhancement through mesoscale features induced by a landfalling tropical storm

Landfalling tropical cyclones (TCs) pose a multitude of forecast challenges, including high winds, storm surge, and heavy precipitation. Of these, extreme precipitation and associated flooding are usually the primary cause of damage overall, but their effects can also be felt well inland. Prediction of the rainfall distribution from a landfalling TC is inherently difficult independent of storm intensity, because precipitation maxima are often found at large distances from the center of the storm.

To focus on the features which cause heavy precipitation areas far from the TC center, a list was compiled of named tropical cyclones landfalling between 1972 and 1998. It was decided that weaker tropical cyclones would be more likely to elucidate the features which caused the enhanced precipitation. Tropical Storm Marco (1990) was selected for further study because it exhibited significant rainfall totals over 300 km from the storm center although it never reached hurricane intensity.

This study will analyze TS Marco and the mechanisms which influenced its total precipitation distribution. Three dominant mesoscale phenomena were found to have a major role in the final rainfall pattern: orographic enhancement, cold-air damming, and coastal fronts. The combination of the mesoscale frontal circulation (created by the cold-air damming and coastal front) and large-scale jet dynamics served to further increase overall rainfall totals. Published literature has traditionally shown cold-air damming and coastal fronts to be mostly cool-season phenomena, but this work shows that these features can also be induced by a nearby tropical cyclone. Using archived imagery, upper-air analyses, surface observations, and cross-sections, it will be shown that these factors significantly increased precipitation over near-coastal areas of the southeast U.S. Further analysis and figures are available at http://www.atmos.albany.edu/student/srock/marco.html.