More wind usually common in January and February
SINGAPORE – It has been windier than usual lately – but such conditions are normal for this time of the year.
“Climatologically, Singapore experiences the strongest average wind speed in January and February,” a spokesman for the Meteorological Service Singapore (MSS) under the National Environment Agency told The Straits Times.
The long-term average monthly surface wind speed recorded at the Changi climate station showed wind speeds of about 3m per second in January and February. In other months of the year, the long-term average wind speed usually do not go past 2.5m per second.
Windier conditions are common during the dry phase of the north-east monsoon season, which Singapore is currently in the midst of.
During the north-east monsoon season, winds blow from the north or north-east. This wind direction is driven by differences in atmospheric pressure on the Asian and Australian continents.
As the Asian continent in the northern hemisphere is experiencing winter during this period, air is cooler and sinks, resulting in a high pressure system there.
But in the southern hemisphere, summer conditions in Australia mean there is warmer air. Because warm air rises, a low pressure system develops.
Associate Professor Koh Tieh Yong, a weather and climate scientist at the Singapore University of Social Sciences, explained that as the season progresses, the northern hemisphere gets colder while the summer hemisphere gets warmer, enhancing the pressure gradient.
“The growing pressure difference between the hemispheres drives stronger and stronger winds which are able to penetrate further south, pushing the rain bands located at the head of the winds southwards,” said Prof Koh.
“By February, the winds would have strengthened by quite a bit as experienced in Singapore,” he added.
This is why Singapore experiences two phases to the north-east monsoon. It goes through the wet phase from December to late January, followed by a dry phase till early March. “This is due to the southward shift of the monsoon rain band over the course of the season,” said an MSS spokesman.
She added that Singapore has been in the dry phase of the northeast monsoon since early this month.
Prof Koh said the ongoing La Nina event – which is a climate phenomenon that brings more rain here – implies a stronger thermodynamic drive for the monsoon system, leading to stronger seasonal winds on average.
Following a woman’s death on Feb 18 after a tree fell on her in Marsiling Park, there was speculation on social media that the recent winds had caused it to fall.
However, Dr Lahiru Wijedasa, a former senior arborist with Singapore Botanic Gardens, said that multiple factors could have contributed to the tree falling.
He also said that photographs and videos taken of the tree at the Marsiling site had shown that the tree likely had structral issues. “If the tree was structurally compromised, it would eventually have fallen whether or not it was windy,” he said.