As September ushers in the early days of autumn in London, the city undergoes a gentle shift from the warmth of summer to the cooler, crisper air of fall. This transition period is marked by mild temperatures, moderate rainfall, and fluctuating sunshine — all contributing to a comfortable and scenic time to visit or live in the UK capital.
Typical Average Temperature in London in September
The average temperature in London during September is approximately 16°C (61°F). This median value reflects both daytime highs and overnight lows, offering a balanced overview of the city’s early autumn climate. The month is characterized by a progressive cooling trend, where the beginning of the month tends to be warmer than the end.
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Monthly Average Temperature: 15.9°C to 16°C (60.6°F to 61°F)
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Daily Highs: Generally range from 18°C to 21°C (64°F to 70°F)
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Nighttime Lows: Typically drop to between 11°C and 13°C (52°F to 55°F)
London’s early September weather often mimics late summer, with occasional warm spells. As the days shorten and the sun’s intensity diminishes, temperatures gradually decline, especially during the latter half of the month.
Daily Temperature Breakdown: First Half vs. Second Half
Early September (1st–15th): Warmer, Late-Summer Feel
The first half of September tends to retain the warmth of August, with afternoon temperatures frequently reaching 20–22°C (68–72°F). Clear skies are still common, and light layers or even short sleeves can remain appropriate during the day.
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Highs: 20–22°C (68–72°F)
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Lows: 13–15°C (55–59°F)
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Weather Conditions: Dry spells, scattered sunshine, mild evenings
Late September (16th–30th): Noticeable Cooling Trend
The latter half of September brings a cooler, more autumnal atmosphere. Mornings and evenings begin to feel brisk, and temperatures typically settle around 17–18°C (62–64°F) during the day.
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Highs: 17–18°C (62–64°F)
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Lows: 11–12°C (52–54°F)
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Weather Conditions: Cooler mornings, earlier sunsets, possible fog in parks and riverside areas
Record Temperatures in September: Historical Extremes
While the average climate is stable and predictable, exceptional temperature records in London do exist. These anomalies serve as a reminder of the city’s occasionally volatile weather:
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Highest September Temperature Recorded: 32.6°C (90.7°F) at Heathrow Airport in 2016
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Lowest September Temperature Recorded: Around 7°C (44.6°F) during cold snaps, typically near the end of the month
These extremes are rare but highlight the importance of checking daily weather forecasts, especially when planning outdoor events or travel.
Rainfall and Precipitation Levels
September is moderately wet by London standards, with average rainfall between 50–55mm (about 2 inches) across the month. Rain typically falls over 8 to 11 days, but heavy downpours are infrequent. Instead, light showers or drizzle are more common, usually brief and scattered.
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Average Rainfall: 50–55mm
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Average Rainy Days: 8–11
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Type of Rain: Light, short-lived showers; rare thunderstorms
A compact umbrella or light waterproof jacket is often sufficient for navigating September rain in the city.
Sunlight and Day Length in September
September in London sees a steady decrease in sunlight hours as the month progresses. Daylight reduces by approximately 1.5 to 2 minutes per day, resulting in shorter evenings by the end of the month.
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Average Daily Sunshine: 5–6 hours
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Daylight Duration on September 1st: Sunrise around 6:15 AM; Sunset around 7:45 PM
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Daylight Duration on September 30th: Sunrise around 7:00 AM; Sunset around 6:45 PM
This seasonal change offers an excellent chance to witness autumn foliage in parks like Hyde Park, St James’s Park, and Greenwich Park under golden-hour lighting.
Humidity, Wind, and Atmospheric Conditions
September’s atmosphere is characterized by moderate humidity levels, averaging 74–77%, contributing to that unmistakable early-autumn freshness in the air. Unlike summer, when still days can create a heavy, muggy feel, September’s cooler temps and light winds make for refreshing outdoor conditions.
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Average Humidity: 74–77%
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Average Wind Speed: 12–13 km/h (7–8 mph)
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Prevailing Wind Direction: Southwesterly
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Fog Risk: Low, but possible in early mornings in green or river areas
Wind tends to remain gentle, rarely reaching speeds that would cause disruption. London remains very walkable and pleasant for sightseeing throughout the month.
What to Pack for London in September
Packing for a London trip in September requires layering and flexibility, due to the shift in temperatures and the possibility of occasional rain. Mornings and evenings can be cool, while midday can still be pleasantly warm.
Recommended Items:
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Light jacket or cardigan
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Umbrella or rainproof jacket
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Comfortable shoes (for walking city streets and parks)
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Sunglasses for occasional bright sunshine
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A scarf or wrap for chillier evenings
Fashion in London during this month starts reflecting autumn trends, so layering isn’t just practical — it’s stylish.
