February 2, 2023

La Nina is behaving badly and could impact Caribbean hurricanes


This map shows the tracks of all tropical cyclones in the 2020 Atlantic hurricane season. The points show the location of each storm at 6-hour intervals.
Source – Master0Garfield. Public Domain (CC0 1.0)

La Nina is a natural but potent weather event linked to more drought and wildfires in the western United States and more Atlantic hurricanes. 

But for some strange reason, La Nina has defied the climate models this year and is sticking around for a third straight year, according to the Associated Press.

The cold anomalies associated with the La Nina phase are for now stable, extending their weather influence into the Summer season. And this is not the first time this extension of the cold phase has happened.

Scientists are noticing that in the past 25 years the world seems to be getting more La Ninas than it used to and that is just the opposite of what their best computer model simulations say should be happening with human-caused climate change.

“They (La Ninas) don’t know when to leave,” said Michelle L’Heureux, head of the National Oceanic and Atmospheric Administration (NOAA) forecast office for La Nina and its more famous flip side, El Nino.

You can nicely see the cold anomalies returning in the central and western tropical Pacific. Peak cold anomalies are now focused more on the eastern regions, where the trade winds have re-intensified, creating a stronger upwelling effect. NOAA – 29 April, 2022.

A recent update from NOAA’s Climate Prediction Center explained:

“Though La Niña is favored to continue, the odds for La Niña decrease into the
late Northern Hemisphere summer (58% chance in August-October 2022)
before slightly increasing through the Northern Hemisphere fall and early
winter 2022 (61% chance).

During the last four weeks, equatorial SSTs were below average across most of the Pacific Ocean. Equatorial SSTs were above average near Indonesia and the western Atlantic Ocean.”

This trend could be significant says L’Heureux. There’s a small chance that this effect could be random, but if the La Nina sticks around this winter, as forecast, that would push the trend over the statistically significant line, which is key in science, she said.

L’Heureux’s own analysis shows that La Nina-like conditions are occurring more often in the last 40 years. Other new studies are showing similar patterns.

Flooding in Puerto Rico during a tropical storm in 2011.
Source – DHS/FEMA, Public Domain

Why is this Important for the Caribbean?

ENSO is short for El Nino Southern Oscillation. This is a region of the equatorial Pacific ocean, that changes between warm and cold phases. Typically there is a phase change around every 1-3 years.

During normal conditions in the Pacific ocean, trade winds blow west along the equator, taking warm water from South America toward Asia. To replace that warm water, cold water rises from the depths, a process called upwelling.

El Niño and La Niña are two opposing climate patterns that break these normal conditions. This is what makes up the El Niño-Southern Oscillation cycle. El Niño and La Niña events occur every two to seven years, on average, but they don’t occur on a regular schedule.

Nevada bans non-functional grass because of exceptional drought
The exceptional drought in the American West has lowered the water level in Lake Mead to just 37 percent capacity.
Image -WildfireTigress
(CC BY-SA 4.0)

During an El Nino, the pressure over the tropical Pacific is lower, with more rainfall and storms in this region. The warmer waters cause the Pacific jet stream to move south of its neutral position. With this shift, areas in the northern U.S. and Canada are dryer and warmer than usual.

But in the U.S. Gulf Coast and Southeast, these periods are wetter than usual and have increased flooding.

The La Nina phase is a “cold event.” During La Niña events, trade winds are even stronger than usual, pushing more warm water toward Asia. Off the west coast of the Americas, upwelling increases, bringing cold, nutrient-rich water to the surface.

This, in turn, pushes the jet stream northward. This tends to lead to drought in the southern U.S. and heavy rains and flooding in the Pacific Northwest and Canada. 

During a La Niña year, winter temperatures are warmer than normal in the South and cooler than normal in the North. La Niña can also lead to a more severe hurricane season.