Weather in Porto in September

How September compares

September is the 3rd warmest month of the year in Porto and ranks 112th of 134 destinations we compare for September - see where else is hot in September. Within Portugal it is 13th of 13 (Portugal in September). Against London's average high of 18.6°C in September, Porto is 5.3°C warmer by day and 4.5°C warmer at night.

Daytime and night-time in September

The typical September day in Porto peaks at 23.9°C, but that is an average: the warmest 10% of days reach 29.6°C or more. Roughly 1 in 3 days top 25°C and 1 in 11 pass 30°C. Nights average 15.7°C; one night in ten drops to 13.0°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest September day here reached 35.9°C (2016-09-06) and the coldest night 9.0°C (1994-09-23).

Rain in September

Some rain (4-8 rainy days): about 6 days with 1 mm or more, 64 mm in total. Year to year it varies a lot - the wettest September was 1999 with 186 mm, the driest 2017 with 2 mm. Humidity averages 76%.

Sea temperature in September

The sea averages 17.5°C - too cold for most (under 18°c). Depending on the year it ranges from 16.3°C to 18.8°C. This is the warmest the sea gets here all year.

Sunshine and daylight

Around 6.8 hours of sunshine a day (estimated from cloud cover), 12.3 hours of daylight: the sun rises about 07:15 and sets about 19:44 local time in mid-September. Average cloud cover is 45%.

Is September a good time to visit Porto?

It is a reasonable choice: warm days. The best months for Porto on our scoring are July, August, September; months averaging 25°C or more: Jul, Aug.

Warm days, but keep a layer for evenings

Pack mainly for warm days, with a jumper or light jacket for evenings. September is among Porto's best months for weather, but it is not a guarantee of hot conditions throughout your stay. Days reach 25°C around 34% of the time, so summer clothing should get use without being your entire wardrobe. Hotter spells are possible: 9% of days reach 30°C, making a slower pace and a break from the midday heat sensible when temperatures climb. At the other end, cooler nights can reach 13°C or lower. This suits travellers who prefer comfortable daytime warmth and do not mind adding layers after dark.

Plan for sunshine with room for rain

There is enough sunshine to make outdoor plans worthwhile, with about 6.8 hours a day within 12.3 hours of daylight. That is not the same as clear skies throughout the day, so avoid treating September as a reliably dry summer month. A light waterproof is a useful addition to your bag, and plans that can shift with the forecast will serve you better than a rigid outdoor schedule. The monthly average cannot tell you how rain will fall during your particular stay. Porto makes sense if you can accept occasional wet weather; it is less convincing if uninterrupted sunshine is the main reason for travelling.

The sea is colder than the air suggests

Warm afternoons do not translate into warm swimming water. The sea averages 17.5°C in September, which is cold rather than comfortably swimmable for most holidaymakers. The year-to-year range of 16°C to 19°C also suggests you should not count on a warm-water exception. If swimming is central to your holiday, this is the clearest drawback to choosing Porto then. You may still enjoy a brief dip if you are used to cold water, but plan around your own tolerance rather than the daytime air temperature. For a trip centred on walking and spending time outdoors, the sea temperature matters much less.