Weather in Porto Alegre in September

A good month. September is a solid month to be in Porto Alegre. Highs average 21.9 °C, lows 12 °C, and rain falls on 12 days — nothing in the month is working against you.

September ranks 7 of 12 in Porto Alegre: past the worst of the year but short of April, which is the month to book if the dates are open.

This is wet-season rain: 12 wet days and 6 genuinely heavy ones, which in this climate means concentrated downpours rather than all-day grey. The pattern is usually a clear morning and a loud afternoon, so front-load the day and stop fighting the 3pm hour. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

The averages here are honest — no hidden extremes worth planning around. Across the twenty years measured, the hottest September day reached 32.4 °C and the coldest night fell to 1.6 °C, and the wettest single day dropped 89 mm — roughly 57% 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 318 mm against 63 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 157 mm average is a reasonable planning figure, not a promise.

Wind is light at 9 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: 20.6 °C in August, 21.9 here, 24.2 in October. Nothing about the timing within the month matters much.

Daylight in September

11.9 hours of daylight, gaining 0.9 hours across the month. That is between Porto Alegre's extremes of 14.1 and 10.2 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 17.2 °C in September — cold — a quick dip rather than a swim, and a wetsuit if you are in for longer. The sea peaks at 25.3 °C in February and bottoms out at 16.5 °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 Porto Alegre: it scores within 6 points of April without carrying April's prices.

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

September in Porto Alegre versus nearby

If Porto Alegre is one option among several, the nearby comparison is worth making. Curitiba is close enough to be a coin toss — within a degree on temperature, 1 day more rain. São Paulo is a better bet in September — 5.1 °C warmer, 2 days less rain.

So: September is effectively as good as it gets here — 6 points behind April, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Porto Alegre

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