Recent theory suggests that ocean-atmosphere interactions in the western Pacific warm pool are of fundamental importance to interannual variations associated with El Ni¿o and the Southern Oscillation (ENSO). The warm pool encompasses the highest mean sea surface temperatures (SSTs) in the world ocean, intense atmospheric deep convection and heavy rainfall, and the formation of thick salt-stratified barrier layers that help to sustain the high SSTs. This study shows that the eastern edge of the warm pool is characterized by a strong zonal salinity front throughout 2002--2004. The analysis also indicates a tighter empirical relationship than previously observed between the eastern edge of the warm pool, high SSTs, the presence of barrier layers, and the fetch of westerly wind bursts. These results suggest that such a frontal region is a critical in controlling ocean-atmosphere interactions in the western Pacific warm pool and highlight the importance of the upper ocean salinity in climate variability.