Climate averages 1991–2020

Swansea weather
in September.

A mild, wet month: the 4th warmest and the 7th driest of the year.

Long-term climate patterns, not a forecast for a particular trip.

Average high 16.8°C Daytime mean, September

Average low 12.1°C Night-time mean, September

Rainfall 96 mm 13 days with ≥1 mm

Daylight 13 h Sunrise to sunset, per day

September is a mild month in Swansea: daytime highs average 16.8°C and nights cool to about 12.1°C. By daytime temperature it is the 4th warmest of the 12 months.

Expect about 96 mm of rain on roughly 13 days, which makes September a wet month (the 7th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 43 min on an average September day.

The nearest other city in this atlas is Cardiff (55 km away). In September its highs average 17.2°C, about as warm as Swansea, with 74 mm of rain.

Among the 143 cities listed in the United Kingdom, Swansea ranks joint 98th of 143 for the warmest September highs and joint 138th of 143 for the driest September (rainfall, lowest first). The mean September high of those 143 cities is 17.3°C; Swansea is 0.4°C cooler than that mean.

From September to October, average highs fall by 3.1°C to 13.7°C, and monthly rainfall rises from 96 mm to 143 mm.

The annual picture

September in context

30-year average

Average highAverage low°C

Monthly rainfall

Average total · mm

Averages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated

Every month, side by side

Swansea climate table

1991–2020

Monthly climate averages for Swansea, 1991–2020
Month	Average highHigh / low	Average low	Rainfall mm/month	Rain days ≥1 mm/day	Daylight hours/dayDaylight h/day
January	7.7°C4.0°C	4.0°C	128	17.0	8.48 h
February	7.8°C3.7°C	3.7°C	92	13.1	9.910 h
March	9.4°C4.5°C	4.5°C	83	13.7	11.812 h
April	11.8°C6.1°C	6.1°C	69	12.0	13.814 h
May	14.6°C8.8°C	8.8°C	72	12.4	15.616 h
June	16.9°C11.6°C	11.6°C	79	12.2	16.617 h
July	18.5°C13.5°C	13.5°C	86	13.8	16.216 h
August	18.5°C13.8°C	13.8°C	101	14.3	14.615 h
September, selected	16.8°C12.1°C	12.1°C	96	13.2	12.713 h
October	13.7°C9.7°C	9.7°C	143	16.7	10.711 h
November	10.5°C6.9°C	6.9°C	143	17.3	8.99 h
December	8.2°C4.7°C	4.7°C	145	16.8	7.98 h

Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.

Compare places

September in nearby cities

Distance from Swansea

Read the numbers correctly

Climate, not a promise.

These patterns help compare months. They cannot tell you the weather on a specific day of your trip.

Sources, method and limits

How these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Swansea) is explained once on the Swansea year overview and on the Sources, method and limits page.