If you have been holding your breath for the haze to hit Singapore and wonder why it has not, it is because of favourable wind conditions and recent rains.
Over the last two weeks, prevailing winds have blown largely from the south south-west or the south south-east, instead of south-west, which would have transported the haze from Sumatra to Singapore.
Satellite images on the National Environment Agency's (NEA) haze portal showed that winds last month carried a plume of haze caused by fires in Sumatra, Indonesia, north towards the west coast of Peninsular Malaysia, giving Singapore a miss. This caused unhealthy levels of haze on June 24 in several areas, including Selangor and Putrajaya.
Recent rains also lowered the number of fire hot spots in Sumatra, the NEA haze portal showed.
Weather researcher Winston Chow of the National University of Singapore's geography department said recent rains were normal for the ongoing south-west monsoon, but these could end once the El Nino weather phenomenon - linked to drier weather - kicks in later this year as forecast.
"The prevailing winds are also rather variable for now. They should get more south-westerly as we progress into July, August, September," he said. If so, and if fires are present in Sumatra, the haze may hit Singapore, he added.
In Parliament yesterday, Nominated MP Nicholas Fang asked Minister for the Environment and Water Resources Vivian Balakrishnan if the recent weather would prompt a change in the ministry's haze assessment. But Dr Balakrishnan said Singaporeans are well aware that the haze can arrive "unpredictably and very quickly".
"It takes about six hours from the onset of the plume in Riau to be brought across... the narrow straits to us," he said.
The Government has warned that the haze could be imminent for several reasons. The dry season from June to September in Sumatra generally leads to burning as farmers clear land to grow crops. This season's low rainfall could be worsened by El Nino.And the period coincides with the onset of the south-west monsoon, which is likely to carry smoke plumes from Sumatra.
Yesterday, six hot spots were detected in Sumatra. Thundery showers are expected this morning, as well as tomorrow and Thursday. Air quality is expected to be in the moderate range.