Weather in Buenos Aires in September

Prime time. September is about as good as Buenos Aires gets. Highs average 16.9 °C, lows 11.6 °C, and rain falls on 6 days — nothing in the month is working against you.

Buenos Aires barely has seasons. September scores 78 out of 100 against a best of 83 in April — a gap small enough that the month you choose matters far less here than the week you choose.

Rain falls on only 6 days, so an itinerary with no wet-weather fallback is a reasonable risk. Pack for 16.9 °C days and 11.6 °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: the day barely swings — 5.3 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 25.2 °C and the coldest night fell to 5.5 °C, and the wettest single day dropped 82 mm — roughly 99% of the month's rain in one day.

September is moderately variable: 13 mm in the driest year against 204 mm in the wettest, around an average of 83 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind sits around 17.8 km/h — a steady breeze rather than a nuisance, and welcome on the warmer days, and humidity runs at 78%, high enough to notice on the warm days without dominating them.

How September sits in the year

The month is on the way up: 1.9 °C warmer than August, and October adds another 3.1 °C. Late in the month feels noticeably different from the start of it, which is worth knowing if the trip is short.

Daylight in September

11.8 hours of daylight, gaining 1.1 hours across the month. That is between Buenos Aires's extremes of 14.5 and 9.8 hours, so days are long enough not to constrain the plan.

An inland climate

Despite being inland, the year stays fairly even: 18.9 °C between the year's warmest afternoons and coldest nights.

How busy it gets

Busy. Popular without being frantic; book the things you care about, improvise the rest.

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

September in Buenos Aires versus nearby

If Buenos Aires is one option among several, the nearby comparison is worth making. Rosario is a better bet in September — 5.1 °C warmer, the same number of rain days. Mar del Plata is the weaker option in September — 3.4 °C cooler, 3 days more rain.

So: September is effectively as good as it gets here — 5 points behind April, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Buenos Aires

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