The warming, called an El Nino, is expected to lead to fewer Atlantic hurricanes.
For the US, it could bring more rain next winter for drought-stricken California and southern states, and even a milder winter for the frigid northern tier next year.
The National Oceanic Atmospheric and Administration today issued an official El Nino watch. NOAA Climate Prediction Center director Mike Halpert said the warming should be in place this summer.