Peninsula-Scale Convergence in the South Florida Sea Breeze

Computations of peninsula-scale convergence in southern Florida reveal that daily-averaged surface convergence on sea-breeze days with relatively little rainfall is larger than on days with widespread rain. This negative correlation between surface convergence and area-averaged rainfall occurs as a result of significantly less surface convergence in the late afternoon and early evening on those days with considerable rainfall. The decrease in sea-breeze convergence during the late afternoon of the days with extensive rainfall is apparently a consequence of the downdrafts and thunderstorm-generated circus cloud cover produced by the deep convection that forms in the sea-breeze convergence zones. Before the typical midafternoon maximum of deep convection on sea-breeze days, there is no significant difference between the surface convergence averaged for days with widespread rain and for days with little rain. Important differences are observed, however, in the middle troposphere, where the sea-breeze days with widespread rain are more moist and have cooler temperatures than the days with little or no rain. The observations suggest that both the magnitude and timing of the convective response to the sea-breeze forcing during the afternoon are very sensitive to the moisture amount and some-what less sensitive to the thermal stability in the midtroposphere.