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More rainy days ahead in Singapore, triggered by two weather phenomena

People in Singapore should brace themselves for wetter weather over the next few months.

The Republic's weather service says two phenomena, one in the Pacific and the other in the Indian Ocean, are set to bring more rain clouds over the region.

One of the phenomena, La Nina, affects global temperatures and brings drought to some places and floods to others. The United Nations said earlier this month that La Nina is likely to continue for months, and possibly even into 2023.

La Nina refers to the large-scale cooling of surface temperatures in the central and eastern equatorial Pacific Ocean that occurs every two to seven years. In South-east Asia it normally triggers above-average rainfall and flooding. The present La Nina episode started in 2020 and has continued largely uninterrupted.

The Meteorological Service Singapore (MSS) said in a report earlier this year that La Nina contributed to last year's heavy rainfall across the island, the second highest on record after 2007 - which was also a La Nina year.

A second weather phenomenon, called the Indian Ocean Dipole (IOD), is also set to make the weather ripe for rain. An MSS spokesman said a negative IOD was predicted to develop during June to August.

When the IOD is in a negative phase, winds intensify along the equator towards South-east Asia and Australia, bringing warm waters around the region and providing lots of energy and moisture to form rain clouds.

"With La Nina conditions and a potential negative IOD, these climate drivers point towards wetter than average rainfall for Singapore for the June to August 2022 period," the spokesman told The Straits Times.

MSS said the prevailing La Nina conditions were predicted to weaken during June to August. "Thereafter, there is some uncertainty as to whether the weak La Nina conditions will persist through the rest of the year or return to El Nino-Southern Oscillation (Enso) neutral conditions."

La Nina and its sister phenomena El Nino are the cool and warm phases of the recurring Enso climate pattern across the tropical Pacific.

The pattern shifts back and forth every two to seven years, and each phase triggers global changes in temperature and rainfall. El Nino events typically bring warmer and drier conditions to South-east Asia.

MSS said La Nina events typically have the strongest effect on Singapore during the south-west monsoon season (June to September), leading to higher than average rainfall.

But the effect on Singapore's temperature is less pronounced compared with the effect on rainfall, the weather agency added.

Combined, La Nina and a negative IOD event can bring wetter than average rainfall to Singapore during the south-west monsoon, MSS said, adding that one of the wettest south-west monsoons occurred in 2010, when there was a strong La Nina and negative IOD.

Despite La Nina's typically cooling impact on the region, Singapore has been suffering weeks of sweltering weather. April and May this year have seen some of the highest temperatures recorded in Singapore.

For the rest of this month, the wet weather might help to slightly ease the warm and humid conditions felt in recent weeks, MSS said in its latest fortnightly outlook.

"On most days, the daily temperature is forecast to range between 24 deg C and 33 deg C. There could still be a few warm days with daily highs exceeding 34 deg C," it said.

While both weather phenomena are naturally occurring events, climate scientists say global warming is supercharging the world's weather towards greater extremes.

"Human induced climate change amplifies the impacts of naturally occurring events like La Nina and is increasingly influencing our weather patterns, in particular through more intense heat and drought and the associated risk of wildfires - as well as record-breaking deluges of rainfall and flooding," secretary-general of the UN World Meteorological Organisation, Professor Petteri Taalas, said earlier this month.

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