There's no distinct seasons in Singapore, and you are as likely to get sunny weather one day as a downpour on the next. the later months like Nov and Dec are a bit wetter though, while June and July are usually the drier months. Floods, though rare, are not unheard of in Singapore. However, they are rarely life-threatening and lasts only for several hours.
Even with this wet and wetter pattern, there is a degree of predictability. The rain tends to start mid or late afternoon and sunny mornings can turn into wet afternoons, or vice versa. Be on the safe side and always take an umbrella with you - good for rain and shade.
However, with the changes in climate the weather is becoming a little bit erratic. Water spouts have been seen in Singapore harbor. In December 2006 the monsoon moved from it's easter track to a path that took it over Singapore and parts of peninsular Malaysia - Johor Bahru had the worst flooding in 100 years.
