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.

W​eak La Niña conditions have formed and will likely persist according to an update released by NOAA Thursday. Here is what you can expect and how long it will last.

A long-awaited La Nina has finally appeared, but the periodic cooling of Pacific Ocean waters is weak and unlikely to cause as many weather problems as usual, meteorologists said Thursday. La Nina, the flip side of the better-known El Nino,

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