Rainy weather in S'pore could persist till March 2021 because La Nina

La Nina conditions are expected to intensify in the upcoming months.

Zhangxin Zheng | November 30, 2020, 11:53 AM

La Nina-like conditions have descended upon the Southeast Asia region since August 2020, with further cooling in September, according to Meteorological Service Singapore (MSS).

These conditions include changes in the sea surface temperature, cloudiness, and winds over the tropical Pacific Ocean.

MSS updated on Nov. 12 that La Nina is expected to last till March 2021.

Expected to last till March 2021

According to MSS, the model predictions from international climate centres show that the La Nina conditions will strengthen from moderate to strong in the next two months.

La Nina conditions will weaken from February 2021 onwards but will persist till March.

What is La Nina?

La Nina is the sister phenomenon of El Nino.

El Nino is usually associated with hot and dry weather in Southeast Asia.

La Nina and El Nino are opposite phases of a climate phenomenon called the El Nino Southern Oscillation (ENSO).

El Nino vs La Nina

During an El Nino event, Southeast Asia sees hotter weather and less rain in general.

But during a La Nina event, the opposite happens.

Singapore's location

Singapore is situated in the western Pacific.

This location is between the Pacific Ocean, to the east, and the Indian Ocean, located to the west.

Why El Nino produces less rain & hotter weather

The western Pacific is much warmer than the east under normal conditions.

Predictable trade winds mainly blow from east to west.

Warm water is confined around the maritime continent where Singapore is located.

But trade winds weaken during El Nino and the warm water moves towards the central Pacific Ocean to the east.

The rain clouds follow, taking away rain and resulting in hotter weather.

Why La Nina brings more rain

During La Nina, the opposite happens.

Trade winds intensify, concentrating the moisture supply and stimulates rain clouds formation over the maritime continent.

El Nino and La Nina are caused by changes in atmospheric pressure and sea surface temperatures in the tropical Pacific Ocean.

Can't predict if there will be more rain yet

Based on the sea surface temperature anomaly indicator of the equatorial region, Nino3.4 index, the amount of rainfall from December to March currently has a weak correlation with ENSO.

Therefore, Nino3.4 index is not a good predictor of rainfall amount for Singapore in the coming months.

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Top photo by Zheng Zhangxin