Weather in Porto Alegre in December

A good month. December is a solid month to be in Porto Alegre. Highs average 28.2 °C, lows 18 °C, and rain falls on 12 days — nothing in the month is working against you.

December ranks 9 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.

Rain on 12 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Pack for 28.2 °C days and 18 °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: 8 days top 30 °C — hot spells arrive, but they break. Across the twenty years measured, the hottest December day reached 37.3 °C and the coldest night fell to 9.9 °C, and the wettest single day dropped 59 mm — roughly 54% of the month's rain in one day.

December is moderately variable: 35 mm in the driest year against 221 mm in the wettest, around an average of 110 mm. Roughly two Decembers in three land near that average, and the third does something else entirely.

Wind is light at 9.1 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 79%, high enough to notice on the warm days without dominating them.

How December sits in the year

Temperatures hold steady either side: 26.1 °C in November, 28.2 here, 29.4 in January. Nothing about the timing within the month matters much.

Daylight in December

December is at or near the longest days of Porto Alegre's year: 14.1 hours of daylight, holding steady all month. Evenings are the real gain — dinner outdoors still happens in full light.

Sea temperature

The sea sits at about 22.7 °C in December — comfortable for a proper swim. 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

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.

December 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, 10 days more rain. São Paulo is the weaker option in December — within a degree on temperature, 10 days more rain.

So: December works, with April the better month by 7 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in Porto Alegre

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