A long-awaited La Niña has finally appeared, but meteorologists say the periodic cooling of Pacific Ocean waters is weak and unlikely to cause as many weather problems as usual.

A La Niña advisory is in effect. La Niña occurs when the ocean's surface temperatures in the central and east-central equatorial Pacific reach a specific cooler-than-average level, as circled below. In addition, the response of atmospheric circulations globally are also considered.