September weather forecast and climate
Belfast, United Kingdom

A close-up view of the Northern Ireland City Hall located in Belfast, United Kingdom
A close-up view of the Northern Ireland City Hall located in Belfast, United Kingdom

What is the temperature in September in Belfast?

In September, the average high-temperature is 16.4°C (61.5°F), and the average low-temperature is 9.5°C (49.1°F).

How much does it rain in Belfast in September?

In Belfast, in September, it is raining for 12.6 days, with typically 75.6mm (3") of accumulated precipitation.

When is the sea warmest in Belfast?

September is the month with the warmest seawater in Belfast, United Kingdom, with an average sea temperature of 14.3°C (57.7°F). Swimming in 14.3°C (57.7°F) is considered dangerous. Unprotected immersion in temperatures below 10°C (50°F) causes quickly maximum intensity cold shock with hyperventilation.

How cold is the water in September in Belfast?

In September, in Belfast, the average sea temperature is 14.3°C (57.7°F). Swimming in 14.3°C (57.7°F) is considered life-threatening. Even a few minutes in 13°C (55.4°F) water is uncomfortable, and swimming below 10°C (50°F) may cause total loss of breathing control and cold shock, depending on a person's physique.
Average temperature in September - Belfast, United Kingdom
  • Average high temperature in September: 16.4°C

The warmest month (with the highest average high temperature) is July (18.8°C).
The month with the lowest average high temperature is January (7.1°C).

  • Average low temperature in September: 9.5°C

The month with the highest average low temperature is July (11.7°C).
The coldest month (with the lowest average low temperature) is February (1.6°C).

Average rainfall in September - Belfast, United Kingdom
  • Average rainfall in September: 75.6mm

The wettest month (with the highest rainfall) is October (89.6mm).
The driest month (with the lowest rainfall) is May (57.3mm).

Average rainfall days in September - Belfast, United Kingdom
  • Average rainfall days in September: 12.6 days

The month with the highest number of rainy days is January (14.8 days).
The month with the lowest number of rainy days is June (11.3 days).

Average sea temperature in September - Belfast, United Kingdom
  • Average sea temperature in September: 14.3°C

The best month for swimming (with the highest average sea temperature) is September (14.3°C).
The coldest month (with the lowest average sea temperature) is March (8°C).

Average daylight in September / Average sunshine in September - Belfast, United Kingdom
  • Average daylight in September: 12.7h

The month with the longest days is June (Average daylight: 17.2h).
The month with shortest days is December (Average daylight: 7.4h).

  • Average sunshine in September: 4h

The month with most sunshine is May (Average sunshine: 6.4h).
The month with least sunshine is December (Average sunshine: 1.5h).

Average UV index in September - Belfast, United Kingdom
  • Average UV index in September: 3

Months with the highest UV index are June and July (UV index 6).
Months with the lowest UV index are January and December (UV index 0).

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