More rain likely in Southeast Asia in upcoming months as experts detect La Nina-like conditions

Less rain is expected to fall on Singapore for the rest of September, but wetter weather could be expected in the months ahead.

The weatherman has declared the onset of La Nina-like conditions in the region this month, after being on watch since July for the climate phenomenon that brings rainier weather to Southeast Asia.

La Nina is the "crybaby" sister to El Nino — the phenomenon usually associated with hot and dry weather in South-east Asia.

"La Nina-like conditions have been detected in the west Pacific. These include characteristic changes in the sea surface temperature, cloudiness, and winds in the tropical Pacific Ocean," the Meteorological Service Singapore (MSS) of the National Environment Agency told The Straits Times in response to queries last week.

This follows a Sept 14 update by the United States' National Oceanic and Atmospheric Administration (NOAA), which had also concluded that La Nina conditions are present.

But the MSS spokesman noted that as La Nina events typically occur over several months, more observations are needed before a La Nina event can be declared.

La Nina and El Nino are opposite phases of a climate phenomenon known as the El Nino Southern Oscillation.

Both phenomena are caused by changes in atmospheric pressure and sea surface temperatures in the tropical Pacific Ocean, and have opposite effects on the weather over the maritime continent, which includes Singapore and Indonesia.

Under normal conditions, the western Pacific — where countries like Singapore and Indonesia sit — is much warmer than the east.

The reason lies in the way the winds blow. In the tropical Pacific Ocean, winds mainly blow from east to west.

These predictable trade winds, as they are known, keep warm water confined around the maritime continent.

But during an El Nino, the trade winds weaken. This means the pool of warm water is no longer confined to the region.

As the warm water moves towards the central Pacific Ocean, the rain clouds follow.

This is why during an El Nino event, South-east Asia experiences less rain, and hotter weather.

But during a La Nina event, the opposite happens.

The trade winds intensify, causing warm water to be more tightly confined around the maritime continent. This concentrates the moisture supply which fuels the formation of rain clouds that brings more rain.

But weather scientist Koh Tieh Yong from the Singapore University of Social Sciences (SUSS) noted that the rainfall experienced in the first half of this month is not likely to have been influenced by La Nina.

Instead, the increased rainfall is likely due to the observed stronger winds blowing from the tropical Indian Ocean, which caused more rain clouds to form over South-east Asia, bringing more rain, he added.

Associate Professor Koh noted that as a La Nina event is still some way from fruition, its influence on September weather here is weak.

This means that for this month, other factors - such as atmospheric oscillations in the Indian Ocean - could have a stronger influence on weather here.

Singapore sits between the Indian Ocean, located west of the country, and the Pacific Ocean, to its east.

"Watch out for La Nina's potential occurrence in the Pacific and the associated wetter regional weather in next two months (Oct-Nov) instead," he added.

This article was first published in The Straits Times. Permission required for reproduction.