The haze that shrouded yesterday's skies is expected to persist today, due to winds blowing in smoke from Sumatra, Indonesia, where forest fires are still raging.
Air quality is forecast to be in the low to mid-sections of the unhealthy range and may enter the high section if denser haze is blown in, the National Environment Agency (NEA) said yesterday.
Air quality is considered unhealthy when the 24-hour Pollutant Standards Index (PSI) reading is in the range of 101 to 200.
Reduced visibility is also expected if PM2.5 concentration - referring to particles which are 2.5 microns or smaller - remain elevated, it added.
Singaporeans may get some relief towards the end of this month, with the south-west monsoon season coming to an end.
The inter-monsoon period that follows typically brings more rain and light, variable winds to Singapore and the region and should ease the haze situation, according to the Meteorological Service Singapore.
However, it added that Singapore could still be affected by the haze, depending on the location and extent of the fires in Sumatra and Kalimantan, the direction of the prevailing winds and the frequency of rain.
Yesterday, the 24-hour PSI entered the unhealthy range in the afternoon.
By 7pm, the 24-hour PSI was between 103 and 127. The three-hour PSI - an indicative reading not tied to a health advisory - rose to 177, from below 100 in the morning.
The total number of hot spots detected in Sumatra yesterday was 58. NEA noted that parts of central and southern Sumatra are still affected by moderate to dense haze, and some of the haze has spread to the Straits of Malacca and the sea south of Singapore.
On Saturday, haze caused by intensified forest and land fires in Indonesia's Central Kalimantan spread to the Sulawesi island to its east for the first time this year.
A multinational task force which has been fighting the fires in Sumatra for the past week has met with some success. But dry weather in Indonesia, made worse by an extended El Nino season, has made it harder to completely douse the blazes.
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