Inter-monsoon downpour causes some minor flooding
Fiona Low Straits Times 15 Apr 11;
THE daily double whammy of sweltering noon heat, followed by intense thunderstorms later in the day, can be expected until June as Singapore goes through what is known as the inter-monsoon season.
Such weather is 'typical' of the season - which extends from late March to May and then from October to November - said a spokesman for the National Environment Agency (NEA).
Heavy rains in the late afternoon yesterday caused minor flooding in several areas, said a spokesman for national water agency PUB.
Drains along Stadium Link leading to Old Kallang Airport Road overflowed. Parts of the East Coast Parkway and Tampines Expressway were also affected.
At Old Kallang Airport, several areas were flooded with ankle-deep water. The site is one of the venues for this year's Singapore Biennale and sees more than 400 visitors daily.
Staff from Toast Box cafe there said the outlet had experienced about three floods in the past week though yesterday's situation was the most serious.
However, a spokesman for the Singapore Art Museum, which organised the Biennale, said that no exhibits had been affected. Staff also provided umbrellas to shelter patrons from the rain.
The PUB said that the water in most areas subsided within half an hour.
The inter-monsoon season comes twice a year here - sandwiched in between the south-west (June to September) and north-east (November to March) monsoons.
Contrary to popular belief that the monsoon is defined by heavy rains, the seasons are in fact characterised by wind behaviour, said climate scientist Matthias Roth from the Department of Geography at the National University of Singapore.
During the monsoon season, constant strong winds blow from a uniform direction, either the north-east or the south-west.
The winds come from an area with higher atmospheric pressure - the Tibetan Plateau during the north-east monsoon and Australian region during the south-west monsoon - to an area with lower atmospheric pressure, where Singapore is.
The uniform direction of the wind also lends to more predictable weather as it follows a charted path.
The inter-monsoon period on the other hand, is characterised by weaker winds that do not come from a fixed direction, resulting in the more erratic weather seen now.
During the inter-monsoon season, the sun is also directly above the equator due to the tilt of the earth's axis. This accounts for a higher mid-day temperature for equatorial countries like Singapore.
Incidentally, the hotter temperature is also what causes the downpour later in the day.
As the surface heats up and warm air rises into the atmosphere, it cools down and the water vapour condenses to produce clouds, and eventually rain.
Therefore, higher temperatures in the afternoon will likely result in heavier rains later in the day as more hot air rises to form clouds.
However, the amount and possibility of rain also depends on other factors such as humidity levels, added Dr Roth.
Additional reporting by Leow Si Wan
