Water Vapor Fluxes over the Intra-Americas Sea: Seasonal and Interannual Variability and Associations with Rainfall

Abstract

The seasonal and interannual variability of moisture transports over the Intra-Americas Sea (including the Gulf of Mexico and the Caribbean Sea) is evaluated using the NCEP?NCAR global reanalysis. The seasonal variability of these moisture transports is consistent with previous studies and shows distinctive winter and summer regimes. Boreal winter moisture is mainly delivered to the central United States from the Pacific with some contribution from the Gulf of Mexico. It is during the boreal summer that the moisture flow over the Intra-Americas Sea is most effective in supplying the water vapor to the central United States via the northern branch of the Caribbean low-level jet. The increase of intensity of this jet during July is associated with an increase in evaporation over the Intra-Americas Sea, consistent with midsummer drought conditions over this region. During both summer and winter, the interannual variability of the inflow of moisture from the Intra-Americas Sea into central United States is associated with Caribbean low-level jet variability. The source of the varying moisture is mainly the Gulf of Mexico and the North Atlantic area just east of the Bahamas Islands and the sink is precipitation over east-central United States. The main teleconnection pattern for these interannual variations appears to be the Pacific?North American, although in boreal winter ENSO and possibly the North Atlantic Oscillation may also play a role. During boreal summer, associations with ENSO mainly involve the zonal moisture exchange between the Intra-Americas Sea/tropical Atlantic and the tropical Pacific.