Weather in Sandakan in September

Shoulder season. September is shoulder season in Sandakan — cheaper, quieter, and a genuine gamble. You should expect rain on 28 days of the month, which is more days wet than dry.

Sandakan barely has seasons. September scores 54 out of 100 against a best of 57 in February — a gap small enough that the month you choose matters far less here than the week you choose.

Rain on 28 of the month's 30 days, 7 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 84% nothing dries, including you.

What the averages hide

Averages flatten a month, and this one hides a few things: the day barely swings — 2.3 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 31.3 °C and the coldest night fell to 25 °C, and the wettest single day dropped 110 mm — roughly 48% of the month's rain in one day.

September is moderately variable: 103 mm in the driest year against 804 mm in the wettest, around an average of 230 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 5.3 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 84%, high enough to notice on the warm days without dominating them.

How September sits in the year

Temperatures hold steady either side: 28.6 °C in August, 28.6 here, 28.4 in October. Nothing about the timing within the month matters much.

Daylight in September

Sandakan sits close enough to the equator that daylight barely moves all year — 12.2 hours in September, against a range of just 0.7 hours across the whole calendar. Sunrise and sunset land at roughly the same time whenever you come.

Sea temperature

The sea sits at about 29.5 °C in September — warm enough that the water offers no relief from the heat. The sea peaks at 29.7 °C in May and bottoms out at 27.8 °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 Sandakan versus nearby

If Sandakan is one option among several, the nearby comparison is worth making. Kota Kinabalu is close enough to be a coin toss — within a degree on temperature, 4 days less rain. Zamboanga is close enough to be a coin toss — within a degree on temperature, 2 days less rain.

So: September is effectively as good as it gets here — 3 points behind February, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Sandakan

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