Introduction Normally the West Pacific is moist.
Warm air rises over there and decends in the East Pacific.
This is the Pacific Walker Cell. Over the equator an Easterly wind blows. Together with Southerly winds along the Chilean and Peruvian coasts this causes upwelling of colder water. Most years around Christmas some warmer water appears along the Ecuadorian and Northern Peruvian coasts. Walker Cell circulation is shifted to quite an extent.