Weather in Colombo in September

Shoulder season. September is shoulder season in Colombo — cheaper, quieter, and a genuine gamble. You should expect rain on 22 days of the month, which is more days wet than dry.

September ranks 5 of 12 in Colombo: past the worst of the year but short of January, which is the month to book if the dates are open.

Rain on 22 of the month's 30 days, 5 of them heavy. At that frequency a wet-weather backup is not a contingency, it is the itinerary — book the indoor things first and treat the clear days as the bonus. Natural fibres and a second shirt for the day. At 85% nothing dries, including you.

What the averages hide

Averages flatten a month, and this one hides a few things: the day barely swings — 3.4 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 31.7 °C and the coldest night fell to 24.2 °C, and the wettest single day dropped 42 mm — roughly 26% of the month's rain in one day.

September is moderately variable: 30 mm in the driest year against 333 mm in the wettest, around an average of 162 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 14.7 km/h, so the temperature on the page is close to the temperature on your skin, and humidity at 85% is the real story though — it is the number that decides how the day feels, not the 29 °C.

How September sits in the year

Temperatures hold steady either side: 28.8 °C in August, 29 here, 29 in October. Nothing about the timing within the month matters much. Rain is the thing that moves: October brings 5 days more of it, so the earlier half of a flexible trip is the safer half.

Daylight in September

Colombo sits close enough to the equator that daylight barely moves all year — 12.2 hours in September, against a range of just 0.8 hours across the whole calendar. Sunrise and sunset land at roughly the same time whenever you come.

Sea temperature

The sea sits at about 27.8 °C in September — warm enough that the water offers no relief from the heat. The sea peaks at 29.9 °C in April and bottoms out at 27.2 °C — water lags the air by a month or two, which is why the best swimming often comes after the best weather.

How busy it gets

Quiet. Few other visitors, cheaper rooms, and a real chance some seasonal operators are shut.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in Colombo versus nearby

If Colombo is one option among several, the nearby comparison is worth making. Kandy is close enough to be a coin toss — within a degree on temperature, 5 days less rain. Trincomalee is close enough to be a coin toss — 3.3 °C warmer, 10 days less rain.

So: September works, with January the better month by 13 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in Colombo

See all twelve months in Colombo, or where else to go in September.