The Western Hemisphere warm pool (WHWP), centered in the Intra-Americas Sea between North and South America, plays a key role in climate from the eastern Pacific to Africa. Although smaller than the Indo-Pacific warm pool, the WHWP has a much larger annual cycle and significant interannual anomalies. Almost nonexistent during the boreal winter, in summer the WHWP becomes the dominant tropical heat source for the Western Hemisphere, energizing a Hadley circulation from the WHWP into the Southern Hemisphere. In the summer following many (but not all) El Niño events the WHWP may be twice its normal size, due to inter-ocean forcing of the Atlantic from the Pacific, through the troposphere. In years with large warm pools there is a stronger Hadley flow and greater than normal subsidence over the subtropical southeast Pacific Ocean, and therefore may be a factor in the termination of El Niño events. The WHWP is a major source of summer moisture carried into North America and the eastern North Pacific by the eastern Atlantic trade winds and is thus a key factor for understanding the North American summer monsoon system.

The balance of heat transports that annually form and destroy the WHWP is not well understood. Heat budget analyses have been hampered by large discrepancies between the various surface heat flux data sets based on observations and model reanalyses. We approach this problem through a sequential procedure that allows us to disqualify as being physically inconsistent, four of seven surface heat flux climatologies considered, enabling us to greatly narrow the range of uncertainty in the surface forcing. This approach also allows us to estimate total oceanic fluxes within narrower ranges than heretofore possible and to characterize the seasonal onset and decay of the WHWP.