Abstract
Summer convective regimes over south Florida can be broadly, classified as either sea breeze or disturbed. Sea-breeze circulations develop on one or both coasts on most days with relatively little high cloudiness during the morning hours. The sea breeze strongly modulates the development of deep convection and produces a sharp midafternoon peak in rainfall. Disturbed days, which are characterized by extensive high cloudiness near sunrise, also have a rainfall maximum during the afternoon. Relationships between rainfall and thermodynamic and kinematic variables on disturbed and sca-breeze days have some significant differences. Comparison of rainfall records from the south Florida peninsula with observations from the Florida Keys, where sea-breeze circulations are relatively weak, indicates that the sea breeze accounts for about 35-40% of south Florida peninsula rainfall during the summer months.
Area-averaged rainfall and the time variations of peninsula-scale surface divergence and hourly rainfall on sea-breeze days are affected by the value of midtropospheric humidity, and lower tropospheric lapse rate, wind speed, and wind direction measured at 0700 EST. Days with relatively high humidity and steep lapse rates typically have deep convective activity that tends to develop sooner and reach its peak earlier than normal. Also, on such days surface convergence is significantly less than average in the late afternoon and early evening.Physical and dynamical processes that might account for the smaller values of surface convergence in the late afternoon are discussed.
The magnitude of the low-level wind speed (1000-800 rob) observed at 0700 EST does not greatly affect the timing of peninsula.scale rainfall. Sea-breeze days with weaker than average low-level wind speeds haverelatively large values of surface convergence and more rainfall during the afternoon. There are two sea-breeze regimes for low-level wind speeds > 5 m s-L When the low-level wind blows parallel to the peninsula, the sea-breeze circulation is strong and area rainfall is greater than average. When the wind blows across the peninsula, the sea breeze is absent or weak and rainfall is below average.
