The Southwest Monsoon Season experiences showers and thunderstorm activity between predawn to midday. However, thunderstorms usually last for less than 30 minutes. ‘Sumatra squalls’ are common during this period. These are a line of thunderstorms that develop at night over Sumatra, move to the west coast of Peninsula of Malaysia and hit Singapore during the early morning hours. Heavy rain persists for 1-2 hours, followed by cloudy conditions and light rain until afternoon. This season also experiences spells of dry weather. Sometimes Singapore is engulfed in a smoke haze – the haze is caused by smoke from forest fires in Indonesia that is carried to Singapore by the southeasterly or southwesterly winds.
Separating these two seasons is the inter-monsoon period (April-May and October-November), which experiences showers in the afternoons and early evenings. It is usually hot and dry in the months of May-July and more frequent rain spells occur during November-January.
Based on climate records, November has the highest rain days while February has the lowest. According to the National Environment Agency, Singapore receives 2342.2 mm of rain fall in an average year.