Weather in London in September

Prime time. If you get to pick your dates, September is the one. Highs average 20 °C, lows 10.4 °C, and rain falls on 9 days — nothing in the month is working against you.

September is the highest-scoring month of the twelve. The nearest rival is June, and the month at the other end of the year is January.

Rain on 9 days, 1 of them heavy. Enough to need a plan B, not enough to need a plan around it. 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. Across the twenty years measured, the hottest September day reached 28.3 °C and the coldest night fell to 2.8 °C.

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 76 mm against 17 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 44 mm average is a reasonable planning figure, not a promise.

Wind is light at 11.2 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

The month is on the way down: 2.6 °C cooler than August, with October dropping another 4.3 °C. The first week and the last are not the same trip. Rain is the thing that moves: October brings 5 days more of it, so the earlier half of a flexible trip is the safer half.

Daylight in September

12.7 hours of daylight, losing 1.9 hours across the month. That is between London's extremes of 16.6 and 7.9 hours, so days are long enough not to constrain the plan.

An inland climate

Despite being inland, the year stays fairly even: 21.1 °C between the year's warmest afternoons and coldest nights.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

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

September in London versus nearby

If London is one option among several, the nearby comparison is worth making. Birmingham is the weaker option in September — 2 °C cooler, 2 days more rain. Le Havre is close enough to be a coin toss — within a degree on temperature, 1 day more rain.

So: September is the answer for London. If it is booked out or priced out, June is the next best thing at 3 points behind, and January is the month to keep off the shortlist.

Every month in London

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