Summertime Precipitation Regimes Associated with the Sea Breeze and Land Breeze in Southern Mississippi and Eastern Louisiana

Abstract

This study assesses the monthly climatology of the timing and placement of convective precipitation events induced by sea and land breezes in the Louisiana?Mississippi?Alabama region, and determines possible reasons for the monthly differences. These objectives were achieved through surface wind climatologies and radar composites from 2003 to 2005, supplemented by statistically significant tests. It is shown that June had an easterly?southeasterly wind regime, whereas July and August featured more southerly flow. These wind regimes may have influenced monthly diurnal wind patterns along the coast. While all months showed a typical pattern of sea-breeze evolution, the land breeze demonstrated monthly variations off the Mississippi and Louisiana coasts. July and August feature a westerly land breeze from Louisiana, while the Mississippi land breeze was stronger in August than in July. A daily wind speed minimum offshore from Mississippi indicates a local transition of influence from the land breeze to the sea breeze, and precedes the peak of the sea breeze at the coastline by about 2 h. During the nighttime hours, radar composites show that precipitation is most prevalent offshore of the Louisiana and Mississippi coastline. By 1100 central daylight time (CDT), precipitation is observed over coastal regions. Local afternoon precipitation is widespread throughout the inland areas, while precipitation is minimal offshore. Statistical significance tests show that areal precipitation coverage (APC) increases in mid- to late summer on the Mississippi coast are due to higher precipitable water and, to a lesser extent, additional CAPE. Greater offshore APC in July and August results from the influence of the local land-breeze setup. Convergence of a land breeze from eastern Louisiana and a stronger land breeze from Mississippi provides the additional lift needed to generate convection over a greater area.