Air quality worsened to nearly unhealthy levels yesterday, marking the start to a weekend that would likely remain hazy, forecasts by the weatherman show.
At 6pm yesterday, the 24-hour Pollutant Standards Index, a measure of air quality here, was 98 in southern Singapore - just shy of the 101 threshold indicating unhealthy air quality.
The National Environment Agency (NEA) said in a statement that it detected hot spots in both Sumatra and Kalimantan in Indonesia.
But based on wind direction, it is smoke haze from Sumatra that has been affecting Singapore.
Some 156 hot spots were detected in Sumatra, mainly in the central and southern parts of the Indonesian island.
"Moderate to dense smoke haze continued to emanate from persistent hot spots there, and hazy conditions persisted in Singapore and some parts of Peninsular Malaysia," said the NEA.
There were more hot spots in Kalimantan, with a total of 1,043 detected there yesterday.
The NEA said that widespread smoke haze was observed over many areas in Kalimantan, with some of the pollution blown over to western Sarawak and the surrounding sea areas.
Weather scientist Koh Tieh Yong of the Singapore University of Social Sciences said hot and dry con-ditions are likely to continue in South-east Asia in the weeks ahead.
A persistent cold sea surface anomaly off the west coast of Sumatra is discouraging the for-mation of rain clouds over the region, he noted. This could worsen man-made forest fires in Sumatra and Kalimantan.
Associate Professor Koh added: "Over the past few days, near-surface air turbulence has slowly diffused the haze from the hot spots in Riau and Jambi to our island, compounding the direct transport by winds from hot spots in south Sumatra."
He said: "There is a good chance that hazy days in Singapore will recur in the next few weeks, except when the local rainfall washes out the particulate pollutants."
The NEA said that there may be brief showers in Singapore, but the weather over Sumatra and Kalimantan is forecast to remain generally dry.