SINGAPORE - The sky may occasionally turn hazy over Singapore on Friday (Sept 4), with the 24-hour Pollutant Standards Index (PSI) fluctuating between the high end of moderate and low end of the unhealthy range, the National Environment Agency (NEA) warned on Thursday evening.

Thundery showers are also forecast for Singapore in the late morning and early afternoon on Friday.

Skies were grey on Thursday as Singapore experienced hazy conditions from early morning. At 1pm, the 24-hour PSI was at 80-87, which is within the moderate range. At 8pm it had increased slightly to 82-94. Air is considered unhealthy when the index crosses 100.

The haziness is due to the spread of smoke haze from Sumatra under weakening wind conditions over Singapore. The number of hotspots detected in Sumatra decreased to 111 on Thursday from 395 the day before, the NEA said.

Given the haze forecast, people here are advised to reduce outdoor activities and physical exertion to limit the ill effects from haze exposure. The NEA added that the elderly, pregnant women and children should minimise prolonged or strenuous outdoor physical exertion, while those with chronic lung or heart disease should avoid such activities.

Those who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.