34°C but feels like 42°C: Why S'pore weather feels extra hot in May

Mothership Explains: Urban development, humidity and your location in Singapore each play a part in making the weather feel like "literal hell" in May.

Joshua Lee| June 02, 2022, 11:21 AM

Follow us on Telegram for the latest updates: https://t.me/mothershipsg

It's 7am. You step out of your house, ready for the commute to work, only to find yourself starting to perspire heavily in places you never even knew you could perspire from.

And before you know it, you're walking around with swampy pits and Airism shirts that are perpetually stained with sweat spots.

It's quite normal for temperatures in Singapore to soar in the months of April, May, and June. But the past two months seemed especially hot.

In April, the temperature peaked at 36.8°C, the second highest temperature recorded in Singapore ever. Last month, Singapore also recorded the highest temperature for May: 36.7°C.

Why so hot???

First off: It's terribly humid in Singapore all year round.

Situated at the equator, Singapore experiences high temperatures as it receives the most direct sunlight. The surrounding water evaporates at a high rate, giving rise to an abundance of water vapour.

Since we are an island, this water vapour gets carried inland by the sea breeze. Warm air is also able to hold more water vapour than cool air.

The Meteorological Service Singapore provides some rather helpful information about the relative humidity in Singapore.

Typically in the mornings (just before sunrise), over 90 per cent of the air is saturated with water vapour. By the afternoon, if there's no rain, this figure drops to around 60 per cent.

Compounding the humidity is the urban heat island effect. Urban structures around us -- like buildings, roads, and pavements -- retain heat very well. Too well, in fact.

A 2006 study estimated that the excess heat generated by the urban heat island in Singapore could reach about 7°C.

Aside from solar radiation, the urban heat island effect in Singapore is also caused by the heat generated by motor vehicles, factories, and even household appliances like air-conditioners.

A CNA programme illustrated the urban island heat effect in 2019 by comparing temperatures in rural Lim Chu Kang and Orchard Road. The latter was four degrees warmer.

The inter-monsoon season

But aside from these factors which are constant throughout the year, what made May 2022 particularly hot?

The answer to that is the inter-monsoon season.

On March 16, 2022, the Meteorological Service Singapore forecast the onset of an inter-monsoon period.

As the name suggests, the inter-monsoon periods fall between (inter) two monsoon seasons -- the Northeast Monsoon season (around December to early March) and the Southwest Monsoon (around June to September).

Singapore has two inter-monsoon periods: Late March to May; October to November.

During an inter-monsoon period, Singapore experiences what meteorologists call "light and variable winds" which refer to very, very gentle breezes that come from different directions.

It sounds idyllic but in real life, it means that the winds aren't strong enough to ventilate the heat and humidity that we stew in.

Combine all of the above together and you get days like this:

Feels like we're suffocating in this heat.

Your location in Singapore also makes a difference.

The southern part of Singapore usually experiences lower temperatures because of the sea breeze that blows in from the Singapore Strait, reported The Straits Times.

The northern part of Singapore lies furthest away from the Singapore Strait and is backed by Malaysia's land mass, and hence it gets less of the cooling sea breeze.

This means northern locations like Sembawang, Admiralty, and Woodlands typically experience higher temperatures, especially during the inter-monsoon periods.

But here's a little bit of good news

Now that we're in June, you can expect some respite from the heat thanks to the Southwest Monsoon.

While the Southwest Monsoon season typically brings less rainfall compared to the rest of the year, it brings stronger winds and the occasional Sumatra squall, which is a line of thunderstorms that moves eastwards over Southeast Asia.

When a Sumatra squall moves over Singapore, typically overnight or in the morning, we experience sudden, gusty winds and heavy rain that can last up to two hours.

Satellite imagery of a Sumatra squall moving over Singapore. Credit: MSS

Just yesterday (June 1), the Meteorological Service Singapore forecast more showers in the first half of June, compared to the second half of May, with low-level winds blowing in from the southeast.

Unfortunately, you can expect warm and humid weather to continue in these two weeks, with temperatures expected to reach up to 35°C on days with no rain.

The met service is also expecting a mass of dry air to blow over Southeast Asia from the Indian Ocean, bringing fair and warm weather over Singapore in these two weeks.

There you have it: The reason why this season tends to be extra hot and humid.

In fact, it might get even hotter in future, in line with global trends.

Singapore is heating up twice as fast as the rest of the world -- at around 0.25°C every 10 years -- thanks to a combination of the island's natural humidity and the city state's urban developments.

In 2019, a senior research scientist with the MSS Centre for Climate Research Singapore warned that Singapore's maximum daily temperature could reach 37°C by the year 2100.

The average daily maximum air temperature has risen over the years. Credit: SingStat.

Welp. Time to stock up on Airism t-shirts, maybe.

Mothership Explains is a series where we dig deep into the important, interesting, and confusing going-ons in our world and try to, well, explain them.

This series aims to provide in-depth, easy-to-understand explanations to keep our readers up to date on not just what is going on in the world, but also the "why's".

Related article

Top image credits: Interwebs, iPhone weather app