Lots of rain where the water is warmest. Thermocline is deep in the western Pacific and shallow in the eastern pacific. A shallow thermocline means that waves can easily bring cold water up from below.
Pressures RISE in the western Pacific and FALL in the eastern Pacific.
Sort of the opposite of El Nino. Stronger than normal trade winds mean MORE warm water piled up in the western Pacific and MORE cold water upwelling in the eastern Pacific.