Weather in Lisbon in September

How September compares

September is the 3rd warmest month of the year in Lisbon and ranks 94th of 134 destinations we compare for September - see where else is hot in September. Within Portugal it is 9th of 13 (Portugal in September). Against London's average high of 18.6°C in September, Lisbon is 6.1°C warmer by day and 6.6°C warmer at night.

Daytime and night-time in September

The typical September day in Lisbon peaks at 24.7°C, but that is an average: the warmest 10% of days reach 29.4°C or more. Roughly 1 in 2 days top 25°C and 1 in 15 pass 30°C. Nights average 17.8°C; one night in ten drops to 16.0°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest September day here reached 35.7°C (2018-09-24) and the coldest night 12.1°C (2017-09-24).

Rain in September

Some rain (4-8 rainy days): about 4 days with 1 mm or more, 29 mm in total. Year to year it varies a lot - the wettest September was 2002 with 124 mm, the driest 2017 with 1 mm. Humidity averages 73%.

Sea temperature in September

The sea averages 19.2°C - bracing (18-22°c). Depending on the year it ranges from 18.1°C to 20.8°C. For the warmest sea here, come in August (19.2°C).

Sunshine and daylight

Around 7.9 hours of sunshine a day (estimated from cloud cover), 12.2 hours of daylight: the sun rises about 07:18 and sets about 19:46 local time in mid-September. Average cloud cover is 35%.

Is September a good time to visit Lisbon?

Yes - it is one of the better months: warm days, manageable rain and long sunny days. The best months for Lisbon on our scoring are July, August, September; months averaging 25°C or more: Jul, Aug.

Warm afternoons, with room for hotter spells

Lisbon in September suits travellers who want to spend much of the day outside but would rather not plan everything around heat. The average daytime high is 24.7°C, although 42% of days reach 25°C, so do not assume every afternoon will feel equally warm. Lightweight, breathable clothes are a practical choice, and it makes sense to leave room for a shaded break around midday when it feels hot. Evenings are milder rather than reliably balmy: the average night low is 17.8°C. Take a light jumper or jacket if you expect to sit outside after dark, rather than packing only for summer afternoons.

Plenty of daylight, but keep plans flexible

With about 7.9 hours of sunshine within 12.2 hours of daylight, September gives you a useful amount of time for outdoor plans. You need not squeeze everything into the brightest part of the day, and sun protection still belongs in your bag. Rain is a possibility rather than a reason to rule the month out: about 4 days receive measurable rain. A compact umbrella or light waterproof is sensible, but there is little reason to pack as though wet weather will dominate. Keep outdoor plans flexible enough to swap them around if rain is forecast, rather than expecting an entirely dry stay.

The sea is the compromise

If swimming is central to your holiday, September's water temperature deserves more attention than the air temperature. The sea averages 19.2°C, which is bracing rather than comfortably warm, with a year-to-year range of 18°C to 21°C. It may suit you if you enjoy a cool dip, but it is a weaker choice if you want to spend long stretches floating in warm water. Pack swimwear if that appeals, along with something dry to put on afterwards. For a trip centred on walking and time outdoors, the warm afternoons are a stronger selling point than the prospect of swimming.