Singapore has a hot and humid climate throughout the year. Basically the Island doesn’t have a fix set of season. Being on the Equator the weather is pretty stable year round with the average low of 20 degree Celsius to average high of 30 degree Celsius. There are two main monsoon seasons in Singapore: Northeast Monsoon Season (December-March) and the Southwest Monsoon Season (June-September). The other significant season is the inter-monsoon period (April-May and October-November).
Peak Season: The best time to visit Singapore city is in the month of June- July & November-December when the temperature is most comfortable and like most of the other South-east Asian countries have school holidays. Note that this is also the peak season to visit Singapore.
Feb-April: These months between the summers and winters are quite pleasant with plenty of outdoor activities available and also to experience the festivities of Chinese New Year.
So, the best time to visit Singapore is in the months of June to July and November to December.