Characteristics of Extreme Summer Convection in the Tropical Americas

Temporal and spatial characteristics of extreme convection over Central America, the Caribbean and Northern-South America are analyzed using the summer months of 14 years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar version 7 data and European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis fields. The 3-dimensional reflectivity field is analyzed to identify three types of extreme systems: storms with deep convective cores, storms with wide convective cores and storms containing broad stratiform regions.

The preferred locations of deep convection (convective cores extending ≥ 10 km in height) are centered mainly over land in the regions of western Mexico, South Florida, Cuba and Northern Colombia and Venezuela. Wide convective regions (contiguous convective cores over a horizontal area ≥ 1,000 km2) extend over both land and ocean regions near the location of deep convective systems, while broad stratiform regions (contiguous stratiform echo over areas ≥ 50,000 km2) occur mainly over the Tropical Pacific and Atlantic oceans within the confluence of the intertropical convergence zone. Regions of extreme deep convection are located in a climatological minimum of precipitation. On the other hand, regions of robust mesoscale convective systems (i.e., wide convective and broad stratiform regions) correspond well with the climatological heavy precipitation. Composite analysis, in seasonal and diurnal time scales, of the synoptic conditions leading to the forms of extreme convection provide insights into the forcing mechanisms in which these extreme systems occur in the tropical Americas. In addition, statistical analysis of rain amounts is used to account for how much of the total precipitation is due to a particular type of extreme convection in relation with their size, location, topography and synoptic characteristics. These results are compared with similar analyses of extreme convection over the subtropical regions of continental South America, South Asia, and for tropical oceanic regions.