September 2018 was cooler than average (13.0°C versus an average of 13.4), wetter than average (41.40 mm versus an average total of 36.68) and windier than average (a wind run of 2502 miles versus an average of 2162).
September 2018 was cooler than average with the maximum being 23.9°C recorded at 15:29 on the 2nd, 0.1°C above the average high. The minimum temperature was 3.2°C, equalling the lowest ever September temperature recorded on September 22nd 2012. The maximum temperature on the 22nd, recorded at 14:02, was only 11.9°C making it the lowest daily maximum since May 2nd, when the maximum temperature was only 11.4°C. It was the lowest September maximum temperature since 17th September 2013 when the temperature only reached 9.9°C. The average temperature for the month was 13.0°C. The daily low was 9.1°C, 0.5°C below the average low. The warmest day was the 2nd with an average temperature of 18.8°C, with the coldest day being the 24th with an average of 8.4°C.
The highest dew point was 17.6°C at 12:39 on the 3rd. The minimum dew point was 2.0°C at 07:04 on the 24th. The monthly average dew point was 9.9°C. The high wind chill was 23.9°C at 15:29 on the 2nd, with the low wind chill being 3.2°C at 07:09 on the 24th. The average monthly wind chill was 12.7°C. The maximum heat index was 23.9°C recorded at 15:29 on the 2nd. There were 119.33 hours of sunshine, with the sunniest day being the 1st when 8.05 hours were recorded.
September 2018 was wetter than average with 41.4 millimetres of rain recorded on 14 days. The wettest day was the 20th when 19.4 millimetres was recorded. This was the second wettest day of 2018. Only April 2nd was wetter when 21.0 millimetres was recorded. The highest rain rate was 52.2 millimetres recorded at 14:45 on the 20th. The yearly rainfall total is now 409.4 millimetres, 105% of what is normally expected by the end of September.
The highest barometric pressure was 1038.2 millibars at 00:42 on the 25th. This was the highest pressure since 1043.2 was recorded on December 28th 2016. The lowest barometric pressure was 988.7 millibars at 01:09 on the 21st. The average pressure in the month was 1018.5 millibars. The highest humidity was 98% and the monthly average humidity was 83%. The lowest humidity was 38% at 17:02 on the 27th.
Winds were stronger than average with a wind run of 2502 miles, compared to the average of 2162 miles. The highest wind gust in the month was 39 mph recorded at 14:48 on the 19th. This was the highest wind gust since January 18th 2018 and the third highest of the year. This was also the second highest wind gust recorded in September, beaten only by the 39.1 mph recorded on September 12th 2011. The average gust speed in the month was 5.5 mph, equalling the mean. The average wind speed was 3.5 mph, also equalling the mean. The maximum wind speed was 19 mph at 14:37 on the 19th. The predominant direction was south-westerly (222°).
The maximum high solar radiation recorded at 12:51 on the 9th was 983 w/m². The average solar radiation for the month was 107 w/m². The highest U.V. Index was 4.0 recorded at 12:21 on the 9th.