Coastal precipitation enhancement over the Southeast U.S. due to mesoscale features induced by near-shore tropical cyclones

Landfalling tropical cyclones present a multitude of forecasting challenges, but accurately predicting the overall rainfall distribution is especially difficult. Unlike storm surge or high winds, which generally decrease in magnitude and impact away from the eye, substantial precipitation maxima and associated flooding problems can often be found far from the storm center. Significant topographic variations within 400 km of the southeast U.S. coast can also enhance a nearby tropical cyclone's precipitation distribution through the inception of cold-air damming and coastal fronts. Although most prevalent during early winter, cold-air damming along the eastern slopes of the Appalachians can be actuated by a proximate tropical cyclone in warmer months. The cold-air damming may then help strengthen a coastal front, which forms because of onshore flow at the coast.

Tropical Storm Marco (1990) was responsible for greater than 350 mm of precipitation at many locations near the southern U.S. Atlantic coast. The topography of the southeast U.S. played a major role in the overall rainfall distribution; much of the heaviest precipitation occurred because of mesoscale features which formed due to interactions between the southern Appalachians and Marco. While at tropical storm intensity and 400 km away, Marco expedited cold-air damming along the eastern side of the Appalachians, which in turn helped to strengthen a coastal front which formed just inland of the coast. These features and their effect on the storm-accumulated precipitation will be examined through the use of the NCEP/NCAR North American Regional Reanalysis (NARR), the NCEP Unified Precipitation Dataset (UPD), and surface observations archived at NCAR. Further analysis and figures are available at http://www.atmos.albany.edu/student/srock/marco.html.