Thundery Showers on Most Days in Second Half of September 2021

Singapore, 16 September 2021 – The weather for the rest of September 2021 is forecast to be similar as that in the first fortnight of the month, with thundery showers expected on most days. For the coming fortnight, the daily maximum temperature is forecast to range between 32°C and 33°C on most days, and with daily highs of around 34°C on a few days.

2      The prevailing Southwest Monsoon conditions in the region are forecast to persist for the rest of September 2021. During the period, the low-level winds are expected to blow mostly from the southeast or southwest, and occasionally shift to blow from the south in the later part of the month.

3      On most days in the coming fortnight, short-duration thundery showers are forecast over parts of the island between the late morning and afternoon. In addition, with a low-pressure system forecast to develop over the northern South China Sea, this could trigger the development of Sumatra squalls over the Strait of Malacca and bring widespread thundery showers and gusty winds to Singapore between the predawn and morning on some days. The overall rainfall for September 2021 is forecast to be above average over most parts of the island.

4      During the second fortnight of September 2021, the daily temperature is forecast to range between 24°C and 33°C on most days. There could still be a few warm days with the daily maximum temperature reaching around 34°C. The weather during the night can be warm and humid with minimum night-time temperatures of around 28°C particularly over the south-eastern parts of the island. This occurs when the prevailing southeast winds bring warm and humid air from the sea over the land.

5      For updates of the daily weather forecast, please visit our MSS website (, NEA website (, or download the myENV app.


REVIEW (1 – 15 September 2021)

6      In the first fortnight of September 2021, Southwest Monsoon conditions prevailed over the region. During this period, the low-level winds blew from the southeast or southwest.

7      In the first two weeks of September 2021, thundery showers fell over parts of the island in the afternoon on most days due to strong day-time heating of land areas. On a few days, the eastward passage of Sumatra squalls from the Strait of Malacca toward the South China Sea brought thundery showers over Singapore in the predawn and early morning. On 2 September 2021, large-scale convergence of winds in the surrounding vicinity led to the development of a Sumatra squall over the Strait of Malacca. The passage of the squall brought widespread moderate to heavy thundery showers and gusty winds over Singapore in the early and predawn hours. The highest daily total rainfall recorded that day was 123.6mm at Ang Mo Kio. This was the highest daily total rainfall for the first half of September 2021. At the Changi climate station, the total rainfall recorded in the first two weeks of September 2021 (up to 15 September 2021) was 119.2mm, which is close to the average monthly rainfall of 124.9mm for September.

8      The rainy weather and cloudy skies in the first fortnight of September 2021 brought relatively cool conditions on most days. There were four days in the fortnight where the daily maximum temperature was above 34.0°C. The highest daily maximum temperature of 34.5°C was recorded at Marina Barrage on 5 September 2021 and the lowest daily minimum temperature of 22.0°C was recorded at Tengah on 7 September 2021.

9      Rainfall was above average over all parts of the island in the first half of September 2021. The highest anomaly of 108% above average was recorded at Jurong Pier. The anomaly was lowest at Sembawang at 17% above average.





Long-term Statistics for September
(Climatological reference period: 1991 – 2020)

Average daily maximum temperature: 31.6 °C
Average daily minimum temperature: 25.2 °C
Average monthly temperature: 28.0 °C
Average rainfall: 124.9 mm
Average number of rain days: 13


Historical Extremes for September
(Rainfall since 1869 and temperature since 1929)

Highest monthly mean daily maximum temperature: 33.0 °C (2019)
Lowest monthly mean daily minimum temperature: 22.4 °C (1930)
Average monthly temperature: 28.0 °C
Highest monthly rainfall ever recorded: 440.4 mm (1988)
Lowest monthly rainfall ever recorded: 22.8 mm (2019)