Weather in Cartagena in September

Shoulder season. September is shoulder season in Cartagena — cheaper, quieter, and a genuine gamble. You should expect rain on 26 days of the month, which is more days wet than dry.

September ranks 8 of 12 in Cartagena: past the worst of the year but short of January, which is the month to book if the dates are open.

Rain on 26 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 82% nothing dries, including you.

What the averages hide

Averages flatten a month, and this one hides a few things: 10 days top 30 °C — hot spells arrive, but they break; the day barely swings — 2 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 32.3 °C and the coldest night fell to 25.9 °C, and the wettest single day dropped 78 mm — roughly 43% of the month's rain in one day.

September is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest September on record still delivered 335 mm against 57 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 182 mm average is a reasonable planning figure, not a promise.

Wind is light at 11 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 82%, high enough to notice on the warm days without dominating them.

How September sits in the year

Temperatures hold steady either side: 30 °C in August, 29.5 here, 29 in October. Nothing about the timing within the month matters much.

Daylight in September

Cartagena sits close enough to the equator that daylight barely moves all year — 12.2 hours in September, against a range of just 1.2 hours across the whole calendar. Sunrise and sunset land at roughly the same time whenever you come.

Sea temperature

The sea sits at about 29.2 °C in September — warm enough that the water offers no relief from the heat. This is the warmest the water gets all year.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

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

September in Cartagena versus nearby

If Cartagena is one option among several, the nearby comparison is worth making. Barranquilla is close enough to be a coin toss — within a degree on temperature, the same number of rain days. Medellín is a better bet in September — 4.6 °C cooler, 1 day less rain.

So: September is a compromise. January is 35 points better and is what Cartagena is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Cartagena

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