Warm season lightning distributions over the Florida Peninsula as related to synoptic patterns

Abstract

Cloud-to-ground lightning data from the National Lightning Detection Network are examined over the Florida peninsula during the warm seasons of 1989 through 1998. The lightning data are stratified according to the location of the subtropical ridge (i.e., north of Florida, south of Florida, and within Florida) as well as other common flow types. Each day is placed into a flow regime based on radiosonde-derived low-level winds at three stations within the study area. Maps of lightning flash density are generated for each flow regime over hourly, daily (24 h), and nocturnal periods. Results for the 24-h period indicate that complexities in the Florida coastline produce four areas of relatively large flash densities: near Tampa, Fort Myers, West Palm Beach, and Cape Canaveral. Nocturnal lightning is found to occur mostly offshore-related to the Gulf Stream, coastline orientations, the prevailing flow, and land breezes. The location of the subtropical ridge with respect to the Florida peninsula is found to play an important role in the spatial and temporal distribution of lightning. For example, when the large-scale flow is from the southeast, the east coast seas breeze and its associated lightning are relatively weak. However, the west coast sea breeze is strong and remains near the coastline, producing the most lightning near Tampa. Conversely, when the large-scale flow is from the southwest, there is relatively little convection along the west coast, but major lightning activity occurs along the east coast.