Friday morning saw temperatures dip below 22C in Singapore. This may not seem particularly cold, but it depends what you are used to.

Singapore is a little over one degree north of the equator, and every day of the year, the expected maximum temperature is at least 30C. Every night, it drops no lower than 23C. Relative humidity remains high, always over 85 percent.

According to data on the Meteorological Service Singapore website, its stations in Admiralty and Ang Mo Kio recorded 21.9C on Thursday night. For comparison, the lowest temperature recorded in Singapore, since records began in 1929, was 19.4C in 1934.

This spell of abnormally cool weather is the result of a monsoon burst combined with a Sumatra squall. This is the wet season during the northeast monsoon and spells of heavy rain do occur. On Monday, and unusually for January, a squall of wind from Sumatra caused a burst of rain: 45mm fell in three hours, bringing flooding to eastern Singapore.

It has been raining continuously since Wednesday and temperatures have been steadily dropping. Since the Sumatra squall, winds have been blustery and from just west of north. Conditions should return to normal by the end of the weekend.

Singapore has not had the worst of it. Heavy rain has been falling during the last two days throughout peninsular Malaysia. In Mersing, on the east coast and some 150km to the north of Singapore, 330mm have been recorded over the last two days. That exceeds the average for the whole of January.

Kuala Lumpur has felt the cool weather, too. The maximum temperature on both Thursday and Friday was 25C. On average, a January day should bring 32C. Overnight lows have also been dropping, hitting 21C on Thursday night, but only two degrees below average. The lowest temperature recorded in Kuala Lumpur in 56 years of recordings is 17.8C.