Dear Loves,
I got this question a lot because I am always talking about La Niña during my storm coverages. Today, I would like to explain what La Niña actually is.
NOAA, in a publication late last week, stated that La Niña conditions have developed, as sea surface temperatures anomalies (SSTAs) across the central and east-central equatorial Pacific on Niño-3.4 and Niño-4 regions were -0.6 °C and -0.7 °C, respectively. La Niña conditions in the equatorial Pacific are expected to continue, with an 87% chance of La Niña in December 2021-February 2022. PAGASA has it that La Niña has developed in the tropical Pacific a day after.
ENSO Status of Various Agencies:
- NOAA: La Niña present
- PAGASA: La Niña present
- BOM: La Niña Alert. La Niña conditions, with 70% to emerging by Winter 2021-22.
- JMA: Neutral conditions with 60% to emerging by Winter 2021-22, 40% to continue neutral conditions.
- KMA: Not stated but based on “forecast” on their site, it shows à La Niña development by Winter 2021-22.
- WMO (September): Neutral conditions with 40% to emerging by Winter 2021-22, 60% to continue neutral conditions.
What’s La Niña, and how does it happen?
La Niña is the cooling of the ocean surface and subsurface in the Central and Eastern tropical Pacific Ocean. La Niña events begin in autumn, mature during winter, spring, and early summer, then start to decay in late summer. Events generally end in the autumn. SST anomalies less than or equal to 0.5 °C (0.9 °F) in the Niño 3.4 region (comprising portions of Niño regions 3 and 4, from 170°W to 120°W longitude) are indicative of ENSO excellent phase (La Niña) conditions. Niño 3.4 SST anomalies are averaged over the three months ending with the current month, and that value is called the Oceanic Niño Index (ONI). If the ONI exhibits warm or cool phase conditions for at least five consecutive deals, it officially becomes an El Niño or La Niña event.
What are the Effects of La Niña?
Over Australia, parts of Oceania and portions of South and Southeast Asia generally have above-average rainfall amounts that cause massive flooding events. It also causes increased tropical activity, as La Niña is characterized by lower-than-normal air pressure over the Western Pacific. It also brings heavy rains to the Pacific Northwest and Canada while bringing drought to the Southern US down to the west coast of South America caused by higher-than-normal air pressure over the Central and Eastern Pacific that causes less tropical activity in these areas.
That is all the information you might want to read to understand the effect of La Niña. Thanks to F13 for providing the sources for this article.
