La Nina has arrived and will stick around — what that means for the dry Southwest

La Nina conditions — the opposite phase of El Nino — have emerged in the tropical Pacific Ocean over the past month.

La Nina conditions — the opposite phase of El Nino — have emerged in the tropical Pacific Ocean over the past month. (CNN Weather)

Estimated read time: 4-5 minutes

ATLANTA — Winter weather, ongoing drought conditions and even the remainder of hurricane season will see impacts from a recent cooling of sea surface temperatures in the Pacific.

La Nina conditions — the opposite phase of El Nino — have emerged in the tropical Pacific Ocean over the past month, the National Oceanic and Atmospheric Administration's Climate Prediction Center said Thursday.

La Nina typically brings conditions that are wetter and cooler than average to the Pacific Northwest and northern Plains, especially during the winter.

In contrast, La Nina means drier and warmer-than-average conditions usually prevail in the South. This could mean the drought-stricken Southwest will likely stay drier. La Nina also was present last winter and worsened the drought situation across the West and Southwest.

The Southeast is also typically drier during a La Nina winter, though before the season starts, it increases the possibility for tropical weather, including hurricanes.

La Nina will persist through winter in the US

La Nina — translated from Spanish as "little girl" — is a natural ocean-atmospheric phenomenon marked by cooler-than-average sea surface temperatures across the central and eastern Pacific Ocean near the equator that consequently impact weather across the world.

"La Nina is anticipated to affect temperature and precipitation across the United States during the upcoming months," the center said as it issued a La Nina advisory Thursday, predicting conditions are present and expected to remain.

The advisory replaces the La Nina Watch, which indicated favorable conditions for development that had been in place since July.

NOAA will release its winter outlook Oct. 21, and the presence of La Nina is expected to weigh heavily in the forecast for the season. The prediction center put the odds near 90% that La Nina would be in place through the winter of 2021-2022.

Both La Nina and El Nino occur every three to five years on average, according to NOAA.

La Nina's impact on the rest of hurricane season

During La Nina, weaker winds between the ocean surface and upper levels of the atmosphere impact global jet streams and can influence the track and severity of winter storms and hurricanes during warmer months.

"La Nina is associated with reductions in vertical wind shear in the Caribbean and tropical Atlantic," said Phil Klotzbach, a research scientist at Colorado State University. "Too much shear is typically what ends the Atlantic hurricane season, so La Niña can extend the active part of the season.

"Last year is a great example of this, as we had six hurricanes and five major hurricanes in Oct.-Nov.," he said. "While we certainly don't expect to see that much activity the remainder of this season, the development of La Nina does leave the window open for more late-season storm activity this year."

At the start of this hurricane season, seasonal forecasters said to look out for La Nina forming in October because it could make the second half of the season active.

Currently, conditions across most of the Atlantic are not conducive for hurricane formation. But this could change in the coming weeks.

La Nina and the climate crisis

While El Nino and La Nina events are regular aspects of global weather patterns, increased global temperatures may temper or change their effects.

La Nina tends to pull down global temperatures, but in recent years, the planet has warmed so fast, it's like hitting a small speed bump at 80 mph — it barely even registers.

It's likely too early to know how climate change will affect those patterns; research is beginning to show how a warming climate may amplify the effects of El Nino and La Nina. Climate change could increase the severity of weather events stemming from El Nino and La Nina patterns, according to a 2018 study on atmospheric conditions that ran simulations of climate conditions.

Top spots on the warmest years list used to be reserved for the strong El Nino years, but human influences have long since overwhelmed the planet's natural temperature regulators. For instance, La Nina was present during parts of 2020, but the year still tied with 2016, an El Nino year, as the hottest on record for the planet.

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