COOL SEPTEMBER, WETTER AND SUNNIER THAN AVERAGE
Armagh Observatory, 3rd October 2025: Armagh Observatory reports that September 2025 was cooler, wetter, and sunnier than average. This was the wettest September at Armagh for three years.
The average temperature this month, defined as half the average of the daily maximum and minimum temperatures, was 13.26 degrees Celsius (55.9 degrees Fahrenheit). This is approximately 0.72 C warmer than the 225-year long-term (1796-2020) average for September at Armagh (12.54 C) but 0.24 C cooler than the most recent (1991-2020) 30-year average (13.50 C). The three warmest days, that is, those with the highest maximum air temperatures, were an unremarkable 19.6 C on the 2nd, followed by 19.3 C on the 17th, and 19.2 C on the 6th. The most recent (1991-2020) 30-year average of the September daily temperature maxima at Armagh is approximately 17.3 C.
The highest minimum air temperature, usually the warmest night, was 15.7 C, which occurred around the time of observations (09:00 GMT) on the 6th but following standard meteorological procedures this temperature minimum was attributed to the 7th. Similarly, the second and third highest minimum air temperatures, both 13.1 C, occurred on the 5th and 18th but were attributed to the 6th and 19th.
The lowest minimum air temperatures, or coolest nights, were 3.3 C on the 24th, followed by 3.7 C on the 23rd and 4.1 C on the 22nd. The coolest day, or lowest maximum air temperature, was 14.2 C on the 21st, followed by 14.3 C on the 20th and 15.0 C on the 27th.
There were six ground frosts this month, the lowest three of which were -2.4 C on the 23rd, -1.8 C on the 22nd, and -1.4 C on the 24th.
Total precipitation was 98.55 mm (3.88 inches) including three trace values, that is, 98.4 mm if trace values are ignored. This is approximately 43% more than the 183-year long-term (1838-2020) average September rainfall at Armagh (68.9 mm) and 52% more than the most recent (1991-2020) 30-year average (65.0 mm).
A bright gibbous moon was seen emerging from behind cloud on the evening of the 4th. Although there were no named storms this month, the afternoon of the 13th was noteworthy for heavy rain including hail and thunder, and for two partial rainbows. The average 09:00 GMT atmospheric pressure reduced to mean sea level this September, was approximately 1011 mbar. This is some 4 mbar lower than the corresponding most recent (1991-2020) 30-year average at Armagh (1015 mbar), indicating the effect of low-pressure weather systems this month and a tendency for greater-than-average rainfall.
Despite a dry spell in the second half of the month this September was wetter than average with 18 rain days, that is, meteorological days with total precipitation greater than or equal to 0.2 mm. The wettest day was the 14th with 23.5 mm of precipitation, followed by the 16th with 15.4 mm and the 2nd with 9.4 mm. The four days beginning the 13th produced more than half the month’s total rainfall.
The few last swallows of the season were noted on the morning of the 5th, and a presumed pair of jays was seen close to the met station on the morning of the 21st. An unusually large flock of approximately 45 gulls was observed during the early evening of the 23rd flying in a north-easterly direction in four “V” formations. The following day, around the same time, a similarly large flock of some 50 gulls was again seen flying in the same direction.
With 130.4 hours of strong sunshine, this September had approximately 16% more strong sunshine than the 140-year (1881-2020) long-term September average at Armagh (112.3 hours) and 14% more than the most recent (1991-2020) 30-year average (114.4 hours). The sunniest days were 9.9 hours on the 23rd, followed by 9.3 hours on the 21st, and 8.9 hours on the 25th.
These data refer to observations at Armagh Observatory, which has been recording the weather at Armagh since 1795.
For further information, please contact:
Professor Mark E. Bailey
Emeritus Director of Armagh Observatory
Armagh Observatory and Planetarium
College Hill
Armagh
BT61 9DG
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