What would you like to know about the weather in Singapore?
Located just one degree north of the equator, Singapore's climate is just about as smooth as its roads. It is near uniformly warm, very humid and with thunderstorms very frequent throughout the year.
Like other countries in the region, Singapore has a monsoon climate, with the southwest and northeast monsoons both bringing rain; while there is a wettest month of the year (November) and a driest (February), you will in all likelihood see some rain during your stay in Singapore.
The southwest monsoon runs from June to September and is characterised by what are known as Sumatra squalls. These squalls are thunderstorms that form over the Indonesian island of Sumatra during the night then they drift across the Straits to the southwest coast of Peninsular Malaysia before reaching Singapore and dumping huge squalls onto the city-state. This is also the period that Singapore can become very smoky due to intentionally lit forest fires in Sumatra. As with the squalls, the prevailing southwesterlies bring the smoke.
The northeast monsoon runs from December to March, with its wettest period being December and January. The rain tends not to be as temperamental as the Sumatra squalls, and instead the rain can come down throughout the afternoon and well into the evening.
Humidity across the year can be debilitating, with 90% (or even 100% during heavy rain) being not at all unusual. Temperatures are far more civil, fluctuating between the mid twenties and early thirties Celsius most days.
You really shouldn't let the weather make this decision for you. Singapore's weather is so consistent throughout the year that there is really little point taking it into consideration.
So instead of worrying about the weather, look instead to its many festivals and other events such as the Singapore Grand Prix that may be of interest to you and just pack a poncho -- you'll need it!