Weather in Lisbon in September

Prime time. If you get to pick your dates, September is the one. Highs average 22.3 °C, lows 17.7 °C, and rain falls on 5 days — nothing in the month is working against you.

September ranks 4 of 12 in Lisbon: past the worst of the year but short of July, which is the month to book if the dates are open.

Rain falls on only 5 days, so an itinerary with no wet-weather fallback is a reasonable risk. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average September reaches 30 °C; the day barely swings — 4.6 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 30.9 °C and the coldest night fell to 14.5 °C.

This is the volatile part. September rainfall has ranged from 0 mm to 101 mm across the twenty years measured — a 101 mm spread around an average of 25 mm. The average is real but almost no individual September looks like it, so treat the figure as the middle of a wide range rather than a forecast.

Wind is light at 14 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 81%, high enough to notice on the warm days without dominating them.

How September sits in the year

Temperatures hold steady either side: 23 °C in August, 22.3 here, 20.4 in October. Nothing about the timing within the month matters much. Rain is the thing that moves: October brings 6 days more of it, so the earlier half of a flexible trip is the safer half.

Daylight in September

12.5 hours of daylight, losing 1.2 hours across the month. That is between Lisbon's extremes of 14.9 and 9.5 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 20.7 °C in September — swimmable, but it takes a moment to commit. This is the warmest the water gets all year.

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 Lisbon versus nearby

If Lisbon is one option among several, the nearby comparison is worth making. Évora is the weaker option in September — 7.9 °C warmer, 1 day less rain. Leiria is close enough to be a coin toss — 6 °C warmer, the same number of rain days.

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

Every month in Lisbon

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