La Niña — which often means a busier Atlantic hurricane season, a drier Southwest and perhaps a more fire-prone California — has popped up in the Pacific Ocean.

The National Oceanic and Atmospheric Administration announced Thursday that a La Niña, the cooler flip side of the better known El Niño, has formed. Meteorologists had been watching it brewing for months.

A natural cooling of certain parts of the equatorial Pacific, La Niña sets in motion a series of changes to the world’s weather that can last months, even years. This one so far is fairly weak and is projected to last through at least February but may not be the two-to-three-year type sometimes seen in the past, NOAA Climate Prediction Center Deputy Director Mike Halpert said.