Singapore: Annual Weather Averages. February is the hottest month in Singapore with an average temperature of 27°C (81°F) and the coldest is January at 26°C (79°F) with the most daily sunshine hours at 9 in September. The wettest month is December with an average of 269mm of rain. The best month to swim in the sea is in April when the average sea temperature is 30 °C (86 °F). Average Temperature: Singapore