The El Niño/La Niña-Southern Oscillation (ENSO) is a description of climate patterns over the Pacific Ocean. Under ENSO normal conditions
- Normal equatorial winds warm as they flow westward across the Pacific.
- Cold water is pulled up along west coast of South America.
- Warming water is pushed toward west side of Pacific.
- Sea surface is warm in the west.
- Hot air rises in western Pacific, travels eastward and cool air descends on South America.
Changes in these conditions lead to El Niño or La Niña phenomena. For more details, see the excellent Wikipedia article on ENSO.
Every month the National Weather Service issues a discussion of ENSO conditions. The link gives you the current discussion and I have not found a way to look at older discussions. So I am keeping an archive of them here.