Singapore enjoyed its first widespread rain in more than 20 days, after what was likely its longest dry spell in the last five years. On Saturday afternoon, thunderstorms brought moderate to heavy rain over the northen, eastern and central parts of the island, tapering off to light rain in the north by about 6.30 pm.

The dry spell had come about because the north-east monsoon's dry phase had set in earlier than usual this year. Last month, Singapore saw just 75.4mm of rainfall, a fraction of the usual amount. But despite being welcome relief from the parched skies of the last three weeks, the rain did not help temper worsening air quality.

The Pollutant Standards Index (PSI), a measure of air quality, crept steadily up throughout the day on Saturday. At 6am the 24-hour PSI was between 24 and 33, while at 6pm it was between 33 and 44.

It is not clear what caused the elevated PSI, but a dry spell has worsened hot spots from slash-and-burn fires in Indonesia's Riau province, while Mount Sinabung in northern Sumatra has been putting out pyroclastic ash since last September. Rainfall for the next week is likely to be below average for most parts of Singapore, said the Meteorological Services Singapore in its forecast for the first fortnight of February.