Monthly climate report
September 2026 in Helsinki
Helsinki's wettest September since 2012, with 161% of the normal rain and 16 days with rain, almost twice the usual. It was mild, with no real heat and no cold nights, ranking seventh-warmest since 1961 but the coolest of the last four.
Published
September 2026 was Helsinki’s wettest since 2012. Kaisaniemi, the weather station in central Helsinki whose record goes back to 1844, collected 89.8 mm3.54 in, 161% of normal, and almost half of it came in the last ten days. At least 1 mm0.04 in fell on 16 days, almost twice the usual 8.6; since 1961 only 1974 and 2012 had more. The sun still logged about as many hours as in an ordinary September, though it came in all-or-nothing days.
Temperatures were mild. The month averaged 13.7°56.7°, 1.4°2.5° above the official 1991–2020 normal and 1.1°2° above the average of the last 30 Septembers. With wind and humidity factored in it felt like 11.4°52.5°, also more than a degree warmer than normal. It was the seventh-warmest September since 1961, and yet the coolest of the last four: 2023, 2024, and 2025 were all warmer.
If you’d rather look at the month as an infographic, check it out here.
- Rainfall
- 89.8 mm3.54 in
- 161% of 1991–2020 · 55.7 mm2.19 in
- 160% of 1996–2025 · 56.0 mm2.20 in
- Days with rain
- 16
- normally 8.6 in 1991–2020
- normally 8.3 in 1996–2025
- at least 1 mm0.04 in a day
- Mean temperature
- 13.7°56.7°
- +1.4°+2.5° vs 1991–2020 · 12.3°54.1°
- +1.1°+1.9° vs 1996–2025 · 12.65°54.77°
- Mean feels-like
- 11.4°52.5°
- +1.3°+2.4° vs 1991–2020 · 10.05°50.09°
- +1.2°+2.1° vs 1996–2025 · 10.23°50.41°
- Sunshine
- 154.8 h
- 104% of 1991–2020 · 149.5 h
- 101% of 1999–2025 · 153.8 h
- at Helsinki-Vantaa
- Warmth rank
- 7th
- warmest September of 66 since 1961
- warmer: 2006, 2018, 2020, 2023–2025
Rain arrived lateCopy link
- Month to date
- Daily rain
- Normal, 1996–2025
- Normal, 1991–2020
Data table
| Date | Rain | Month to date | Normal 1996–2025 | Normal 1991–2020 |
|---|---|---|---|---|
| Tue, September 1 | 0.0 mm0.00 in | 0.0 mm0.00 in | 2.3 mm0.09 in | 2.4 mm0.09 in |
| Wed, September 2 | 0.0 mm0.00 in | 0.0 mm0.00 in | 4.5 mm0.18 in | 4.7 mm0.19 in |
| Thu, September 3 | 0.0 mm0.00 in | 0.0 mm0.00 in | 6.4 mm0.25 in | 6.8 mm0.27 in |
| Fri, September 4 | 0.0 mm0.00 in | 0.0 mm0.00 in | 8.3 mm0.33 in | 8.9 mm0.35 in |
| Sat, September 5 | 4.1 mm0.16 in | 4.1 mm0.16 in | 10.0 mm0.39 in | 10.9 mm0.43 in |
| Sun, September 6 | 0.0 mm0.00 in | 4.1 mm0.16 in | 11.7 mm0.46 in | 13.0 mm0.51 in |
| Mon, September 7 | 1.4 mm0.06 in | 5.5 mm0.22 in | 13.7 mm0.54 in | 15.1 mm0.59 in |
| Tue, September 8 | 3.1 mm0.12 in | 8.6 mm0.34 in | 15.6 mm0.61 in | 17.1 mm0.67 in |
| Wed, September 9 | 4.0 mm0.16 in | 12.6 mm0.50 in | 17.6 mm0.69 in | 19.1 mm0.75 in |
| Thu, September 10 | 5.9 mm0.23 in | 18.5 mm0.73 in | 19.8 mm0.78 in | 21.2 mm0.83 in |
| Fri, September 11 | 1.3 mm0.05 in | 19.8 mm0.78 in | 22.1 mm0.87 in | 23.4 mm0.92 in |
| Sat, September 12 | 2.5 mm0.10 in | 22.3 mm0.88 in | 24.3 mm0.96 in | 25.5 mm1.00 in |
| Sun, September 13 | 1.5 mm0.06 in | 23.8 mm0.94 in | 26.7 mm1.05 in | 27.7 mm1.09 in |
| Mon, September 14 | 0.0 mm0.00 in | 23.8 mm0.94 in | 29.1 mm1.15 in | 29.9 mm1.18 in |
| Tue, September 15 | 0.0 mm0.00 in | 23.8 mm0.94 in | 31.3 mm1.23 in | 31.8 mm1.25 in |
| Wed, September 16 | 5.8 mm0.23 in | 29.6 mm1.17 in | 33.5 mm1.32 in | 33.7 mm1.33 in |
| Thu, September 17 | 2.0 mm0.08 in | 31.6 mm1.24 in | 35.8 mm1.41 in | 35.7 mm1.41 in |
| Fri, September 18 | 9.3 mm0.37 in | 40.9 mm1.61 in | 38.0 mm1.50 in | 37.6 mm1.48 in |
| Sat, September 19 | 6.9 mm0.27 in | 47.8 mm1.88 in | 40.0 mm1.57 in | 39.5 mm1.56 in |
| Sun, September 20 | 0.9 mm0.04 in | 48.7 mm1.92 in | 41.8 mm1.65 in | 41.2 mm1.62 in |
| Mon, September 21 | 0.9 mm0.04 in | 49.6 mm1.95 in | 43.4 mm1.71 in | 42.7 mm1.68 in |
| Tue, September 22 | 0.0 mm0.00 in | 49.6 mm1.95 in | 45.0 mm1.77 in | 44.3 mm1.74 in |
| Wed, September 23 | 1.8 mm0.07 in | 51.4 mm2.02 in | 46.6 mm1.83 in | 45.9 mm1.81 in |
| Thu, September 24 | 13.4 mm0.53 in | 64.8 mm2.55 in | 48.2 mm1.90 in | 47.4 mm1.87 in |
| Fri, September 25 | 16.1 mm0.63 in | 80.9 mm3.19 in | 49.7 mm1.96 in | 48.9 mm1.93 in |
| Sat, September 26 | 8.9 mm0.35 in | 89.8 mm3.54 in | 51.4 mm2.02 in | 50.6 mm1.99 in |
| Sun, September 27 | 0.0 mm0.00 in | 89.8 mm3.54 in | 53.0 mm2.09 in | 52.2 mm2.06 in |
| Mon, September 28 | 0.0 mm0.00 in | 89.8 mm3.54 in | 54.7 mm2.15 in | 54.0 mm2.13 in |
| Tue, September 29 | 0.0 mm0.00 in | 89.8 mm3.54 in | 56.5 mm2.22 in | 55.8 mm2.20 in |
| Wed, September 30 | 0.0 mm0.00 in | 89.8 mm3.54 in | 58.4 mm2.30 in | 57.7 mm2.27 in |
Through September 10, rainfall was on schedule: 18.5 mm0.73 in against a normal 19.8 mm0.78 in. The wet spell of September 16–19 pushed it ahead, to 48.7 mm1.92 in by the 20th, where about 42 mm1.65 in is normal. Then September 24–26 added 38.4 mm1.51 in in three days, 16.1 mm0.63 in of it on the 25th, a record for the date in data going back to 1961 (the previous high was 11.0 mm0.43 in).
The final 89.8 mm3.54 in is 161% of the 1991–2020 normal and the 12th-highest September total since 1961. Of the last 30 Septembers, only 2012 (159.9 mm6.30 in) was wetter.
The rain came in steady, moderate doses. The wettest day, 16.1 mm0.63 in, is about what the wettest day of an ordinary September brings (15 mm0.59 in on average). What stood out was how often it rained: 16 days had at least 1 mm0.04 in, almost twice the normal 8.6, and since 1961 only 1974 and 2012 had more. Counting every day with at least 0.1 mm0.00 in, there were 18 wet days against a normal 13.5, and only two of them stayed under 1 mm0.04 in, where an ordinary September has about five. The last four days of the month were dry.
Two yardsticksCopy link
A climate normal is a 30-year average. The current official period, set by the World Meteorological Organization, is 1991–2020, and it is what the Finnish Meteorological Institute (FMI) publishes for every station. For September at Kaisaniemi that means 12.3°54.1° and 55.7 mm2.19 in of rain. It stays the reference until 2001–2030 replaces it in the early 2030s.
A fixed period ages, and in a warming climate it ages in one direction. So this report also uses a running normal: the 30 most recent complete Septembers, 1996–2025.
For September in Helsinki the two yardsticks are about a third of a degree apart: 12.3°54.1° against 12.65°54.77°. The gap comes from a five-year swap: 1991–1995, which averaged 11.1°52.0°, left the window, and 2021–2025, which averaged 13.4°56.1°, joined it. Over a longer view the shift is larger. The 1961–1990 normal was 11.0°51.8°, and the running 30-year mean bottomed out at 10.8°51.4° for 1968–1997 before climbing to today’s 12.65°54.77°.
- 2026
- Earlier Septembers
- 30-year running mean
- Standard normal
Data table
| Year | Mean | 30-year running mean |
|---|---|---|
| 1961 | 11.3°52.3° | |
| 1962 | 10.4°50.7° | |
| 1963 | 13.7°56.6° | |
| 1964 | 11.1°52.0° | |
| 1965 | 13.3°56.0° | |
| 1966 | 9.9°49.9° | |
| 1967 | 13.6°56.4° | |
| 1968 | 11.7°53.0° | |
| 1969 | 10.6°51.1° | |
| 1970 | 10.7°51.3° | |
| 1971 | 10.1°50.1° | |
| 1972 | 11.1°51.9° | |
| 1973 | 8.3°47.0° | |
| 1974 | 13.3°55.9° | |
| 1975 | 13.6°56.4° | |
| 1976 | 9.0°48.1° | |
| 1977 | 8.9°48.1° | |
| 1978 | 9.7°49.4° | |
| 1979 | 10.9°51.6° | |
| 1980 | 11.9°53.3° | |
| 1981 | 11.2°52.1° | |
| 1982 | 11.3°52.3° | |
| 1983 | 12.3°54.2° | |
| 1984 | 10.8°51.4° | |
| 1985 | 10.4°50.6° | |
| 1986 | 8.4°47.1° | |
| 1987 | 10.0°50.0° | |
| 1988 | 12.1°53.8° | |
| 1989 | 12.1°53.8° | |
| 1990 | 9.6°49.3° | 11.04°51.87° |
| 1991 | 10.8°51.5° | 11.02°51.84° |
| 1992 | 13.0°55.4° | 11.11°52.00° |
| 1993 | 7.7°45.9° | 10.91°51.64° |
| 1994 | 12.0°53.6° | 10.94°51.69° |
| 1995 | 11.9°53.4° | 10.89°51.60° |
| 1996 | 9.8°49.6° | 10.89°51.60° |
| 1997 | 11.7°53.0° | 10.82°51.48° |
| 1998 | 12.2°54.0° | 10.84°51.51° |
| 1999 | 13.4°56.1° | 10.93°51.67° |
| 2000 | 10.5°50.8° | 10.93°51.67° |
| 2001 | 12.8°55.0° | 11.02°51.84° |
| 2002 | 11.6°52.9° | 11.03°51.85° |
| 2003 | 12.1°53.7° | 11.16°52.09° |
| 2004 | 12.8°55.0° | 11.14°52.05° |
| 2005 | 13.1°55.7° | 11.13°52.03° |
| 2006 | 14.0°57.2° | 11.29°52.32° |
| 2007 | 11.9°53.4° | 11.39°52.50° |
| 2008 | 10.4°50.7° | 11.42°52.56° |
| 2009 | 13.5°56.4° | 11.51°52.72° |
| 2010 | 12.2°54.0° | 11.52°52.74° |
| 2011 | 13.6°56.5° | 11.60°52.88° |
| 2012 | 12.5°54.4° | 11.64°52.95° |
| 2013 | 12.6°54.6° | 11.65°52.97° |
| 2014 | 13.1°55.5° | 11.72°53.10° |
| 2015 | 13.7°56.6° | 11.83°53.29° |
| 2016 | 13.3°56.0° | 12.00°53.60° |
| 2017 | 12.1°53.8° | 12.07°53.73° |
| 2018 | 13.9°57.1° | 12.13°53.83° |
| 2019 | 12.2°53.9° | 12.13°53.83° |
| 2020 | 13.8°56.8° | 12.27°54.09° |
| 2021 | 10.4°50.8° | 12.25°54.05° |
| 2022 | 10.8°51.4° | 12.18°53.92° |
| 2023 | 15.8°60.5° | 12.45°54.41° |
| 2024 | 15.5°59.9° | 12.57°54.63° |
| 2025 | 14.4°58.0° | 12.65°54.77° |
| 2026 | 13.7°56.7° |
Against either yardstick, 2026 was clearly above normal but not extreme. Three Septembers in 1991–2020 were warmer (2006, 2018, and 2020), and six in 1996–2025. Measured against the 1961–1990 climate, though, it would have been the warmest September of all 30.
The rain normal has barely moved: 55.7 mm2.19 in for 1991–2020 and 56.0 mm2.20 in for 1996–2025. Both sit well below the 74.1 mm2.92 in of 1961–1990, when Helsinki’s Septembers were wetter.
Day by dayCopy link
- Daily mean
- Low to high
- Normal mean, 1996–2025
- Normal low to high, 1996–2025
- Normal mean, 1991–2020
Data table
| Date | Mean | High | Low | Normal 1996–2025 | Normal 1991–2020 |
|---|---|---|---|---|---|
| Tue, September 1 | 17.0°62.6° | 19.4°66.9° | 15.0°59.0° | 15.0°59.0° | 14.8°58.6° |
| Wed, September 2 | 16.0°60.8° | 20.1°68.2° | 13.0°55.4° | 14.9°58.8° | 14.6°58.3° |
| Thu, September 3 | 16.2°61.2° | 18.7°65.7° | 12.3°54.1° | 14.8°58.6° | 14.4°58.0° |
| Fri, September 4 | 14.6°58.3° | 18.0°64.4° | 11.6°52.9° | 14.7°58.4° | 14.3°57.7° |
| Sat, September 5 | 13.5°56.3° | 18.7°65.7° | 9.7°49.5° | 14.6°58.2° | 14.2°57.5° |
| Sun, September 6 | 12.5°54.5° | 16.4°61.5° | 9.5°49.1° | 14.4°58.0° | 14.0°57.2° |
| Mon, September 7 | 11.7°53.1° | 16.1°61.0° | 5.3°41.5° | 14.3°57.7° | 13.9°56.9° |
| Tue, September 8 | 16.0°60.8° | 17.1°62.8° | 15.0°59.0° | 14.1°57.4° | 13.7°56.6° |
| Wed, September 9 | 16.0°60.8° | 17.8°64.0° | 14.9°58.8° | 13.9°57.1° | 13.5°56.3° |
| Thu, September 10 | 15.3°59.5° | 18.3°64.9° | 12.4°54.3° | 13.8°56.8° | 13.3°55.9° |
| Fri, September 11 | 13.6°56.5° | 17.7°63.9° | 9.5°49.1° | 13.6°56.4° | 13.0°55.5° |
| Sat, September 12 | 12.8°55.0° | 16.9°62.4° | 7.2°45.0° | 13.4°56.1° | 12.8°55.1° |
| Sun, September 13 | 15.1°59.2° | 16.5°61.7° | 11.8°53.2° | 13.2°55.7° | 12.6°54.7° |
| Mon, September 14 | 12.1°53.8° | 17.3°63.1° | 7.4°45.3° | 13.0°55.5° | 12.5°54.4° |
| Tue, September 15 | 11.6°52.9° | 16.6°61.9° | 6.4°43.5° | 12.8°55.1° | 12.3°54.1° |
| Wed, September 16 | 15.0°59.0° | 16.6°61.9° | 13.9°57.0° | 12.6°54.7° | 12.1°53.8° |
| Thu, September 17 | 14.9°58.8° | 17.1°62.8° | 13.0°55.4° | 12.4°54.3° | 11.9°53.4° |
| Fri, September 18 | 14.5°58.1° | 16.5°61.7° | 12.6°54.7° | 12.1°53.8° | 11.7°53.0° |
| Sat, September 19 | 14.7°58.5° | 16.1°61.0° | 12.4°54.3° | 11.9°53.4° | 11.5°52.7° |
| Sun, September 20 | 14.9°58.8° | 16.4°61.5° | 12.8°55.0° | 11.7°53.1° | 11.3°52.4° |
| Mon, September 21 | 13.3°55.9° | 17.7°63.9° | 10.6°51.1° | 11.5°52.7° | 11.2°52.1° |
| Tue, September 22 | 11.6°52.9° | 15.9°60.6° | 8.3°46.9° | 11.3°52.4° | 11.0°51.8° |
| Wed, September 23 | 10.0°50.0° | 11.9°53.4° | 7.7°45.9° | 11.2°52.1° | 10.8°51.5° |
| Thu, September 24 | 12.0°53.6° | 15.3°59.5° | 10.9°51.6° | 11.1°51.9° | 10.7°51.3° |
| Fri, September 25 | 12.6°54.7° | 13.2°55.8° | 11.7°53.1° | 10.9°51.6° | 10.6°51.0° |
| Sat, September 26 | 13.7°56.7° | 14.9°58.8° | 12.6°54.7° | 10.8°51.4° | 10.4°50.8° |
| Sun, September 27 | 12.7°54.9° | 16.6°61.9° | 9.4°48.9° | 10.6°51.1° | 10.3°50.6° |
| Mon, September 28 | 12.1°53.8° | 15.9°60.6° | 7.5°45.5° | 10.5°50.9° | 10.2°50.3° |
| Tue, September 29 | 14.1°57.4° | 15.6°60.1° | 12.9°55.2° | 10.3°50.5° | 10.0°50.0° |
| Wed, September 30 | 11.5°52.7° | 16.0°60.8° | 7.5°45.5° | 10.1°50.3° | 9.8°49.7° |
The month had no real heat and no real cold. The highest temperature was 20.1°68.2° on the 2nd, the only day to reach 20°68°, where a typical September has two. The lowest was 5.3°41.5° on the morning of the 7th. A normal September brings three or four nights below 5°41°; this one had none, for only the eighth time since 1961 (the last was 2023).
What lifted the average instead was a run of mild, cloudy days and nights, with the wind from the southwest more than a third of the time. Of the 30 days, 22 were warmer than the running normal, nine of them by 2°3.5° or more, and only the 7th fell that far below it. The normal daily mean drops by about 5°9° through September, from 15.0°59.0° to 10.1°50.2°. This year it slid only from 16°61°–17°63° to around 12°54°, so the gap widened as the month went on: +0.4°+0.7° in the first ten days, +1.5°+2.7° in the last ten.
- September 1–3 carried summer over, with daily means of 16°61°–17°63° and a high of 20.1°68.2° on the 2nd.
- September 4–7 saw a low pass over on the 5th (994 hPa29.35 inHg in the morning), followed by cool northwesterly air. The 7th was the month’s coldest day relative to normal, −2.6°−4.7°.
- September 8–21 were mostly mild and increasingly wet, apart from two clear, cool days on the 14th and 15th. The 16th to the 20th ran 2.3°4.1°–3.1°5.6° above the running normal, and in the small hours of the 20th gusts reached 17.9 m/s40.0 mph at Kaisaniemi and 21.2 m/s47.4 mph on Harmaja.
- September 22–23 turned briefly chilly. The 23rd peaked at only 11.9°53.4°, and its daily mean of 10.0°50.0° was the month’s one dip to the 10°50° threshold of thermal autumn.
- September 24–26 stayed overcast and added 38.4 mm1.51 in of rain.
- September 27–30 belonged to high pressure, which built to 1039 hPa30.68 inHg by the night of the 30th. Clear nights on the 28th and 30th fell to 7.5°45.5°, but the cloudy 29th was the warmest day of the month relative to normal, +3.8°+6.8°.
Feels-likeCopy link
Feels-like follows FMI’s formula, which adjusts the air temperature for wind chill and, above 14.5°58.1°, for humidity. This report leaves out its sunshine term, which only some stations can supply. Worked out hour by hour, September 2026 felt like 11.4°52.5° on average: 2.3°4.1° cooler than the thermometer, but 1.3°2.3° warmer than the 1991–2020 normal (10.05°50.09°) and 1.2°2.2° warmer than 1996–2025 (10.23°50.41°).
- Daily mean
- Low to high
- Normal mean, 1996–2025
- Normal low to high, 1996–2025
- Normal mean, 1991–2020
Data table
| Date | Mean | High | Low | Normal 1996–2025 | Normal 1991–2020 |
|---|---|---|---|---|---|
| Tue, September 1 | 15.7°60.3° | 17.9°64.2° | 13.9°57.0° | 13.0°55.5° | 13.0°55.4° |
| Wed, September 2 | 14.1°57.4° | 18.0°64.4° | 10.7°51.3° | 12.9°55.2° | 12.8°55.1° |
| Thu, September 3 | 14.0°57.2° | 15.8°60.4° | 10.9°51.6° | 12.8°55.0° | 12.7°54.8° |
| Fri, September 4 | 13.0°55.4° | 15.9°60.6° | 10.2°50.4° | 12.6°54.7° | 12.5°54.5° |
| Sat, September 5 | 12.0°53.6° | 16.4°61.5° | 9.2°48.6° | 12.5°54.5° | 12.3°54.2° |
| Sun, September 6 | 9.3°48.7° | 12.9°55.2° | 6.2°43.2° | 12.4°54.2° | 12.2°54.0° |
| Mon, September 7 | 9.2°48.6° | 13.9°57.0° | 2.8°37.0° | 12.2°53.9° | 12.0°53.6° |
| Tue, September 8 | 13.6°56.5° | 14.9°58.8° | 12.2°54.0° | 11.9°53.5° | 11.8°53.2° |
| Wed, September 9 | 14.2°57.6° | 15.1°59.2° | 12.9°55.2° | 11.7°53.1° | 11.5°52.7° |
| Thu, September 10 | 13.4°56.1° | 15.6°60.1° | 10.8°51.4° | 11.5°52.7° | 11.3°52.4° |
| Fri, September 11 | 10.5°50.9° | 14.7°58.5° | 6.2°43.2° | 11.3°52.3° | 11.1°51.9° |
| Sat, September 12 | 11.1°52.0° | 14.4°57.9° | 6.0°42.8° | 11.1°51.9° | 10.8°51.5° |
| Sun, September 13 | 13.2°55.8° | 14.5°58.1° | 9.7°49.5° | 10.8°51.5° | 10.6°51.0° |
| Mon, September 14 | 10.0°50.0° | 15.0°59.0° | 4.8°40.6° | 10.7°51.2° | 10.4°50.7° |
| Tue, September 15 | 10.1°50.2° | 14.6°58.3° | 5.5°41.9° | 10.4°50.8° | 10.2°50.3° |
| Wed, September 16 | 12.4°54.3° | 14.6°58.3° | 11.6°52.9° | 10.1°50.3° | 9.9°49.8° |
| Thu, September 17 | 12.6°54.7° | 14.4°57.9° | 10.8°51.4° | 9.8°49.7° | 9.6°49.3° |
| Fri, September 18 | 11.8°53.2° | 13.4°56.1° | 10.6°51.1° | 9.6°49.2° | 9.3°48.8° |
| Sat, September 19 | 11.8°53.2° | 13.0°55.4° | 9.6°49.3° | 9.3°48.8° | 9.1°48.4° |
| Sun, September 20 | 11.9°53.4° | 13.2°55.8° | 11.0°51.8° | 9.1°48.4° | 8.9°48.0° |
| Mon, September 21 | 11.4°52.5° | 15.5°59.9° | 8.3°46.9° | 8.9°48.0° | 8.7°47.6° |
| Tue, September 22 | 8.9°48.0° | 13.3°55.9° | 5.2°41.4° | 8.7°47.6° | 8.5°47.3° |
| Wed, September 23 | 7.2°45.0° | 10.6°51.1° | 4.5°40.1° | 8.5°47.4° | 8.3°47.0° |
| Thu, September 24 | 9.4°48.9° | 12.3°54.1° | 7.1°44.8° | 8.4°47.1° | 8.2°46.8° |
| Fri, September 25 | 9.1°48.4° | 10.1°50.2° | 8.3°46.9° | 8.2°46.8° | 8.1°46.5° |
| Sat, September 26 | 10.7°51.3° | 12.0°53.6° | 9.7°49.5° | 8.1°46.5° | 7.9°46.3° |
| Sun, September 27 | 9.9°49.8° | 14.1°57.4° | 6.2°43.2° | 7.9°46.2° | 7.8°46.0° |
| Mon, September 28 | 10.2°50.4° | 13.4°56.1° | 6.1°43.0° | 7.7°45.9° | 7.6°45.7° |
| Tue, September 29 | 11.8°53.2° | 13.6°56.5° | 10.7°51.3° | 7.5°45.5° | 7.4°45.3° |
| Wed, September 30 | 9.5°49.1° | 13.9°57.0° | 6.6°43.9° | 7.3°45.2° | 7.2°44.9° |
The wind took off about as much as usual, 2.3°4.1° against 2.4°4.3° in an average September, so feels-like followed the temperature. The exception was the 6th, when a fresh northwesterly (5.1 m/s11.4 mph on average) made a 12.5°54.5° day feel like 9.3°48.7°: 3.1°5.6° below the normal feels-like, compared with 1.9°3.4° below by temperature alone.
Feels-like ran above normal on 23 of the 30 days, and the gap grew from +0.5°+0.9° in the first ten days to +1.7°+3.1° in the last ten. Nights stood out most: the daily feels-like low averaged 8.6°47.5°, 1.5°2.7° above normal, while the daily high ran 1.1°2° above.
Cold-feeling moments were rare. The month’s lowest feels-like was 2.8°37.0°, at 7 am on the 7th after a clear night (air 5.6°42.1°, wind 2.5 m/s5.6 mph). In a typical September the coldest hour feels like about 0°32°, and 27 of the last 30 had a colder-feeling one. The warmest-feeling hour was 18.0°64.4°, at 4 pm on the 2nd.
Wind also reshuffles the rankings. By temperature, 2026 was the seventh-warmest of the 31 Septembers since 1996, when the hourly record starts; by feels-like it was eighth. The calmer Septembers of 1999 and 2015 drew level or edged ahead, while windy 2020 (4.3 m/s9.6 mph on average) had practically the same mean temperature as 2026 but felt 0.3°0.5° cooler.
Sun in all-or-nothing daysCopy link
For all its rain, September 2026 got its usual share of sun. Kaisaniemi has no sunshine recorder, so this section uses Helsinki-Vantaa airport, which also has an official normal, and Kumpula, three kilometers away. Helsinki-Vantaa logged 154.8 hours of sunshine, 104% of the 1991–2020 normal of 149.5 hours and almost exactly its average since 1999 (153.8 hours). That puts it 13th of the 28 Septembers on record there, right in the middle. Kumpula, in the city, saw 159.5 hours against its average of 147.7 since 2006.
- Sunshine
- Average, 1999–2025
- Daylight
Data table
| Date | Sunshine | Daylight | Average 1999–2025 |
|---|---|---|---|
| Tue, September 1 | 2.7 h | 14.3 h | 5.8 h |
| Wed, September 2 | 8.3 h | 14.2 h | 5.9 h |
| Thu, September 3 | 8.4 h | 14.1 h | 6.0 h |
| Fri, September 4 | 7.8 h | 14.0 h | 6.0 h |
| Sat, September 5 | 7.6 h | 13.9 h | 5.9 h |
| Sun, September 6 | 11.3 h | 13.8 h | 6.0 h |
| Mon, September 7 | 8.2 h | 13.7 h | 5.9 h |
| Tue, September 8 | 0.0 h | 13.7 h | 5.8 h |
| Wed, September 9 | 0.1 h | 13.6 h | 5.7 h |
| Thu, September 10 | 3.7 h | 13.5 h | 5.6 h |
| Fri, September 11 | 10.7 h | 13.4 h | 5.6 h |
| Sat, September 12 | 3.6 h | 13.3 h | 5.5 h |
| Sun, September 13 | 0.0 h | 13.2 h | 5.4 h |
| Mon, September 14 | 11.8 h | 13.1 h | 5.3 h |
| Tue, September 15 | 7.6 h | 13.0 h | 5.2 h |
| Wed, September 16 | 0.0 h | 12.9 h | 5.1 h |
| Thu, September 17 | 5.7 h | 12.8 h | 5.0 h |
| Fri, September 18 | 1.0 h | 12.7 h | 4.9 h |
| Sat, September 19 | 3.2 h | 12.7 h | 4.8 h |
| Sun, September 20 | 4.5 h | 12.6 h | 4.7 h |
| Mon, September 21 | 5.9 h | 12.5 h | 4.6 h |
| Tue, September 22 | 11.2 h | 12.4 h | 4.5 h |
| Wed, September 23 | 0.0 h | 12.3 h | 4.5 h |
| Thu, September 24 | 0.4 h | 12.2 h | 4.5 h |
| Fri, September 25 | 0.0 h | 12.1 h | 4.5 h |
| Sat, September 26 | 0.0 h | 12.0 h | 4.5 h |
| Sun, September 27 | 10.8 h | 11.9 h | 4.5 h |
| Mon, September 28 | 9.6 h | 11.8 h | 4.4 h |
| Tue, September 29 | 0.0 h | 11.7 h | 4.4 h |
| Wed, September 30 | 10.8 h | 11.6 h | 4.3 h |
Nine days had less than half an hour of sun, where an average September has five, and ten had eight hours or more, up from eight. The rain fell on the gray days, as fronts clouded the sky over completely, while the high pressure in between brought clear skies. The 14th was the sunniest day, with 11.8 hours out of a possible 13.1, and the 22nd, 27th, and 30th came close.
The gray days were also the mild ones. The nine dullest days averaged +1.8°+3.2° against the running normal, with nights 3.3°5.9° warmer than usual under the cloud, while the ten sunniest averaged only +0.2°+0.4°: warmer-than-usual afternoons, but clear nights 0.8°1.4° cooler than normal. The dull days also brought 54.6 mm2.15 in of the month’s rain, the sunny ones 2.7 mm0.11 in. Over the month the sun shone for 40% of the hours it was up, and each square meter of ground received 274 MJ of solar energy, 101% of normal.
Out and aboutCopy link
A monthly mean gives the small hours as much weight as the afternoon, though few people are outdoors at 4 am. So this report also looks at the hours from 8 am to 9 pm, the window WeatherSpark uses for its tourism score, which rates how pleasant a place’s weather is for being outside. That is 13 hours a day, 390 over the month.
- Temperature, 8 am–9 pm
- 14.8°58.6°
- +1°+1.8° vs 1996–2025 · 13.8°56.8°
- 6th warmest of 31 since 1996
- Feels-like, 8 am–9 pm
- 12.4°54.4°
- +1°+1.9° vs 1996–2025 · 11.4°52.6°
- 8th warmest of 31 since 1996
- Rainy hours, 8 am–9 pm
- 68
- normally 35.7 in 2013–2025
- most of 14 since 2013; 2019 had 60
- of 390, with at least 0.1 mm0.004 in
By temperature, those hours were as mild as the rest of the month. They averaged 14.8°58.6°, 1°1.8° above the same hours in 1996–2025, and since 1996 only 2006, 2018, and the last three Septembers had warmer days. They felt like 12.4°54.4°, also 1°1.8° warmer than usual.
Rain is where the window tells a different story. It rained in 68 of the 390 hours, almost twice the September average of 36. That’s the most since Kaisaniemi’s hourly rain record began in 2013, well clear of the previous high of 60 in 2019. The nights got wetter too, but less so, with 41 rainy hours, up from the usual 26. On 12 days at least 1 mm0.04 in fell between 8 am and 9 pm, about twice the usual six, and only 16 days stayed dry through the whole window, where about 20 is typical.
What fell by day was mostly light. The window caught 48.2 mm1.90 in, just over half the month’s total and a little less than its usual share, spread over 68 hours; the 41 rainy hours at night brought 41.6 mm1.64 in. The sun, by contrast, kept to its usual hours. Almost all of September’s sunshine falls between 8 am and 9 pm anyway, and at Helsinki-Vantaa it came to 148.8 hours, close to the average of 146.3 since 1999.
Wind, humidity, and cloudCopy link
In other respects the month was ordinary. Mean wind speed was 3.6 m/s8.1 mph against a normal of 3.4 m/s7.6 mph, and ten of the last 30 Septembers were windier. The strongest gust, 17.9 m/s40.0 mph at 5:10 am on the 20th, was beaten in 12 of those 30 years. Relative humidity averaged 84% (normal 82%), more than in all but nine of them. Cloud cover averaged 4.3 oktas (eighths of the sky), with eight mostly clear days and eight overcast ones.
Warmest at sea, coolest at the airportCopy link
| Station | Mean | vs 1991–2020 | vs 1996–2025 | Feels-like | Lowest | Highest | Rain | Top gust |
|---|---|---|---|---|---|---|---|---|
| Kaisaniemi | 13.7°56.7° | +1.4°+2.5° | +1.1°+1.9° | 11.4°52.5° | 5.3°41.5° | 20.1°68.2° | 89.8 mm3.54 in | 17.9 m/s40.0 mph |
| Kumpula | 13.4°56.0° | — | — | 10.7°51.3° | 4.1°39.4° | 21.2°70.2° | — | 19.4 m/s43.4 mph |
| Harmaja | 14.1°57.3° | +1.5°+2.6° | +1.1°+2° | 10.7°51.3° | 8.6°47.5° | 17.9°64.2° | — | 21.2 m/s47.4 mph |
| Helsinki-Vantaa | 12.7°54.9° | +1.1°+2° | +0.9°+1.5° | 10.1°50.2° | 1.6°34.9° | 20.3°68.5° | 101.0 mm3.98 in | 18.4 m/s41.2 mph |
The whole city ran mild and wet. Harmaja, a lighthouse island off Helsinki, was the warmest at 14.1°57.4° and never fell below 8.6°47.5°, with the sea still giving back summer heat. Helsinki-Vantaa airport, 17 kilometers to the north, was the coolest at 12.7°54.9° with a low of 1.6°34.9°, yet still 1.1°2° above its own 1991–2020 normal. It collected 101 mm3.98 in of rain, 164% of normal. Feels-like reorders the list: the open-sea wind cut Harmaja’s to 10.7°51.3°, so the warmest station by thermometer felt 0.7°1.3° cooler than central Helsinki.
Heating and thermal autumnCopy link
September 2026 needed almost no heating. Heating degree days, FMI’s measure of heating demand, only start to add up once a day’s mean temperature drops below 10°50°. That happened just once, on the 23rd, so Kaisaniemi logged 7 degree days, where a normal September has 63. Only two Septembers since 1961 needed less: 1992 and 2023, which needed none.
The same 10°50° line marks thermal autumn, which begins once the daily mean stays below it for good. Apart from the 23rd, September stayed above it, so thermal autumn did not begin during the month.
Clouds brought the rain and the mildnessCopy link
Southwesterly winds and passing fronts wrapped the city in cloud, and the cloud kept the nights from cooling, so the gray days were both the wet ones and the mild ones. Between the fronts, high pressure cleared the sky and brought the month’s usual share of sun. The result was a September with no real heat and no real cold, and the wettest Helsinki has seen since 2012.
About the dataCopy link
- Stations: Helsinki Kaisaniemi (FMISID 100971); Kumpula, Harmaja, and Helsinki-Vantaa for the comparison table. Kumpula has too short a record for normals of its own, Harmaja has no rain gauge, and Kumpula’s gauge missed an hour of the month.
- September 2026: The 10-minute observations this site collects from FMI’s open data, grouped into Helsinki calendar days: daily mean, highest and lowest temperature, and hourly rainfall totals. The month has no gaps.
- History: FMI’s daily observations for 1961–2025, and its hourly observations for wind, gusts, and humidity in 1996–2025. Kaisaniemi’s record goes back to 1844, but the rankings here start in 1961.
- Normals: The 1991–2020 temperature and rainfall normals are FMI’s official values. The running 1996–2025 normal and the day counts (rainy days, days reaching 20°68°, nights below 5°41°) are computed from the same history. Daily normal curves average each calendar day with the week on either side (five days for rain), as on this site’s climate normals card.
- Feels-like: Hourly mean temperature, wind, and humidity through the site’s feels-like formula (wind chill, plus a humidity correction above 14.5°58.1°; no solar radiation), the same way the feels-like normals are built. FMI’s hourly record at Kaisaniemi starts in 1996, so the 1991–2020 feels-like normal covers 1996–2020 and the feels-like rankings start in 1996.
- Sunshine: FMI’s minute-by-minute sunshine and global radiation observations at Helsinki-Vantaa and Kumpula, whose September records start in 1999 and 2006, summed over Helsinki calendar days. The 1991–2020 sunshine and radiation normals are FMI’s official values for Helsinki-Vantaa. Daylight is the time the sun is above the horizon.
- Daytime: The hours from 8 am to 9 pm Helsinki time, as in WeatherSpark’s tourism score. Temperature and feels-like are compared with the same hours in FMI’s hourly record from 1996. A rainy hour is one in which the gauge measured any rain; FMI’s hourly rain totals for Kaisaniemi start in 2013.
- Heating: FMI’s heating degree days. In autumn, each day with a mean temperature below 10°50° adds the gap between that mean and 17°63°.
- Rounding: FMI’s own monthly statistics can differ from these figures by a tenth of a degree or a millimeter or two.