Air pollution levels levelled out in the moderate range yesterday, despite a sudden spike in the late afternoon. The evening Formula 1 practice sessions and concerts also started without any difficulty.
The swift deterioration in the afternoon, however, underscored how unpredictable the haze can be.
Experts had forecast that the weekend would be relatively haze-free, when a tropical storm blowing smoke towards Singapore met land.
The 24-hour Pollutant Standards Index (PSI) hovered within the moderate range (51-100) yesterday.
By 7pm, the 24-hour PSI was between 78 and 90. But the three-hour PSI - an indicative reading - rose to 127, from below 70 in the morning.
Air quality is considered unhealthy when the 24-hour PSI reading is in the range of 101 to 200, and very unhealthy when the readings are between 201 and 300. When it crosses 300, air quality is deemed hazardous.
Haze caused by peatland and forest fires in Indonesia's Kalimantan has continued to spread west to the sea south of Singapore, the National Environment Agency said.
Foreign Minister K. Shanmugam phoned his Indonesian counterpart Retno Marsudi yesterday to express his "deep concern" over the haze, highlighting that its recurrence had both immediate and long-term health impact on Singaporeans and others in the region.
Mr Shanmugam, who is also Minister for Law, emphasised that all ASEAN states should fulfil their obligations under the ASEAN agreement on transboundary haze.
Dr Erik Velasco, a research scientist from the Singapore-MIT Alliance for Research and Technology, confirmed that the typhoon that blew winds from the south-west - the direction of Sumatra, Indonesia - causing the haze to reach unhealthy levels earlier this week, has hit land. This led to the respite over the past few days.
The moderate haze yesterday may not hold if there is even a change of 30 degrees in wind direction, according to Dr Velasco.
Occasional hazy conditions are expected today, with winds blowing from the north-east or east.
The 24-hour PSI is predicted to fluctuate between the high end of the moderate range and the low end of the unhealthy range.
But participants of the Singapore Airlines Singapore Grand Prix are not too worried about their performance being affected.
Red Bull driver Daniel Ricciardo said: "It's not a real concern for me. As long as we can see 50m ahead, which as I understand is the case, I won't complain."
Force India driver Sergio Perez said: "It looks okay at ground level. I'm not sure if the fans are suffering but... there was haze last year too and I didn't feel anything different in terms of visibility and breathing."
Additional reporting by Sanjay Nair and Jonathan Wong
This article was first published on Sept 19, 2015.
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