Singapore has two main monsoon seasons, the Northeast Monsoon season (December to March) and the Southwest Monsoon season (June to September). Separating these two monsoon seasons are relatively short inter-monsoon periods (April to May and October to November). The beginning and end of the monsoons are usually not very well-defined. Hence, from year to year, there could be a slight delay in the onset or cessation of a monsoon period.

Although there are no distinct wet or dry periods, the mean monthly rainfall shows drier weather conditions from May to July and wetter conditions between November and January. February is also a relatively dry month.

Kindly call the following telephone numbers:

Automatic Weather Recording: 65427788
Main Meteorological Office (24hr): 6542 5059
General Office : 6545 7193
Job Opportunities : 6542 1187
Climatological Services : 6545 7197

Meteorological data are obtained from various sources such as through a network of weather observational stations located at various parts of the island. These observational stations include synoptic stations, weather radars, weather satellites, upper air observing stations and lightning sensors, to name a few. Other sources include an exchange of meteorological data with other national meteorological centres in the region through the Global Telecommunication System (GTS) of the World Meteorological Organisation (WMO). The Singapore National Meteorological Center is linked to counterparts in the neighbouring countries by medium to high-speed telecommunication circuits which form part of the Regional Telecommunications Network of the GTS.

Thunder is caused by lightning. The bright light of the lightning flash caused by the return stroke represents a great deal of energy. This energy heats the air in the channel to above 50,000 degrees F in only a few millionths of a second! The air that is now heated to such a high temperature has no time to expand, so it is now at a very high pressure. The high pressure air then expands outward into the surrounding air compressing it and causing a disturbance that propagates in all directions away from the stroke. The disturbance is a shock wave for a short distance, after which it becomes an ordinary sound wave, or thunder. Thunder can seem to go on and on because each point along the channel produces a shock wave and sound wave.

A "Sumatra" squall is a line of thunderstorms which usually develops at night over Sumatra or the Malacca Straits and moves east toward Singapore and Peninsular Malaysia in the pre-dawn and early morning hours during the Southwest Monsoon season. The squall is characterised by the onset of strong gusty surface winds and heavy rain lasting from 1 to 2 hours as they move across the island. Following their passage, cloudy conditions with light rain sometimes persist till the early afternoon.