From the climatic point of view, the Americas warm pools are of interest given their play a prominent role in modulating the summer rainy season in the Mesoamerica and Caribbean. The annual precipitation cycle over this region exhibits a bimodal distribution in this region with maxima during June and September-October and relative minimum during July and August, known as the midsummer drought (MSD). This relative precipitation minimum is, as proposed by Magaņa et al. (1999), a result of air sea interaction processes over Mexican Pacific warm pool.

During 2001 boreal summer the field experiment known as ECAC (Climate Experiment in the Americas Warm Pools) took place in order to test the hypothesis about the Mid Summer Drought (MSD) in Mesoamerica. Four oceanographic/meteorological campaigns were conducted, three in the northeastern Pacific one in the Caribbean Sea.

The primary objective of this study is to examine atmospheric and oceanic conditions for the period of 7 to 27 July, which corresponds to the onset of MSD, where two campaigns took place simultaneously: one over northeastern Pacific and one in the Caribbean Sea. Emphasis is given to the surface radiation budget and surface fluxes analysis, and the maritime boundary layer structure. The impacts of variations of the low-level jet over Caribbean Sea on precipitation, easterly waves and hurricane activity are also discussed.