Weather in Surabaya in September

Shoulder season. September is shoulder season in Surabaya — cheaper, quieter, and a genuine gamble. Highs average 33.8 °C, lows 25.7 °C, and rain falls on 4 days — nothing in the month is working against you.

September ranks 4 of 12 in Surabaya: past the worst of the year but short of August, which is the month to book if the dates are open.

Rain falls on only 4 days, so an itinerary with no wet-weather fallback is a reasonable risk. Pack for 33.8 °C days and 25.7 °C nights; the spread matters more here than any single number.

What the averages hide

Averages flatten a month, and this one hides a few things: 29 days top 30 °C, making the heat continuous rather than occasional. Across the twenty years measured, the hottest September day reached 36.2 °C and the coldest night fell to 22.5 °C.

This is the volatile part. September rainfall has ranged from 0 mm to 141 mm across the twenty years measured — a 141 mm spread around an average of 18 mm. The average is real but almost no individual September looks like it, so treat the figure as the middle of a wide range rather than a forecast.

Wind is light at 11.9 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 61%.

How September sits in the year

Temperatures hold steady either side: 32.4 °C in August, 33.8 here, 33.7 in October. Nothing about the timing within the month matters much. Rain is the thing that moves: October brings 6 days more of it, so the earlier half of a flexible trip is the safer half.

Daylight in September

Surabaya sits close enough to the equator that daylight barely moves all year — 12.1 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 28.3 °C in September — warm enough that the water offers no relief from the heat. The sea peaks at 29.8 °C in April and bottoms out at 28.1 °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

Shoulder. The value months — prices ease off and you get the place closer to itself. September is the value pick for Surabaya: it scores within 11 points of August without carrying August's prices.

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

September in Surabaya versus nearby

If Surabaya is one option among several, the nearby comparison is worth making. Jepara is close enough to be a coin toss — 3.1 °C cooler, 4 days more rain. Semarang is the weaker option in September — within a degree on temperature, 3 days more rain.

So: September works, with August the better month by 11 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in Surabaya

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