September is one of the warmer months of the year in Saint John, with average highs near 18.8°C and lows around 9.5°C (mean 14.2°C). It is about average for rainfall, averaging 98 mm of rainfall and 85% relative humidity across the period.
September is one of the warmer months of the year in Saint John. Across 45 years of records, the warmest September in Saint John was 1999 — when the month averaged 17°C — while the coldest was 1986 at 11.5°C. Typical September days reach 18.8°C with nights near 9.5°C. The long-term trend is warming, about 0.6°C per decade.
September is about average for rainfall in Saint John, averaging 98 mm of rainfall. The wettest September on record was 1999 with 218 mm, while the driest was 2011 at 34 mm.
Relative humidity in Saint John during September averages 85%. The most humid September was 2013 at 88%, and the least humid was 1995 at 79%.
September receives about 3.9 kWh/m²/day of solar energy in Saint John. The sunniest September was 2025 at 4.5 kWh/m²/day, and the cloudiest were 1996, 1997 and 2010, among others at 3.3.
Average wind speed in Saint John during September is 0.5 m/s. The windiest Septembers were 1995, 1996 and 2020, among others at 0.6 m/s, while the calmest were 2023, 2024 and 2025, among others at 0.5 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 13.2°C | 13.6°C | 14.1°C | 14.8°C | 15.4°C | +2.2°C |
| Avg High | 17.9°C | 18.2°C | 18.9°C | 19.5°C | 20.1°C | +2.2°C |
| Avg Low | 8.6°C | 9.1°C | 9.4°C | 10.1°C | 10.8°C | +2.2°C |
| Avg Rain | 88 mm | 112 mm | 91 mm | 107 mm | 89 mm | +1 mm |
September temperatures in Saint John have risen by about 2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -1.3°C (1989) to a record high of 30.6°C (2010).
Rainfall in September is about average for rainfall, averaging 98 mm, with a wettest year of 218 mm.
One of the best times to visit Saint John
September is one of the best times to visit Saint John. Expect days averaging 18.8°C and nights around 9.5°C (mean 14.2°C) — warmer than Saint John's yearly average — with higher rainfall (98 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 20.7°C | 15.3°C | 10.0°C | 24.8°C | 3.6°C | 41 mm | 81% | 0.5 m/s | 4.5 |
| 2024 | 20.2°C | 15.6°C | 11.0°C | 26.0°C | 8.1°C | 48 mm | 86% | 0.5 m/s | 4.2 |
| 2023 | 21.7°C | 16.9°C | 12.1°C | 27.0°C | 5.9°C | 131 mm | 87% | 0.5 m/s | 3.7 |
| 2022 | 19.3°C | 14.9°C | 10.6°C | 26.6°C | 3.2°C | 95 mm | 84% | 0.5 m/s | 3.9 |
| 2021 | 19.7°C | 15.6°C | 11.5°C | 24.4°C | 7.2°C | 150 mm | 87% | 0.5 m/s | 3.6 |
| 2020 | 18.9°C | 14.1°C | 9.3°C | 23.9°C | 2.1°C | 70 mm | 84% | 0.6 m/s | 4 |
| 2019 | 18.1°C | 13.3°C | 8.6°C | 23.4°C | 2.9°C | 133 mm | 85% | 0.5 m/s | 4 |
| 2018 | 19.4°C | 14.5°C | 9.6°C | 26.5°C | 1.6°C | 78 mm | 84% | 0.5 m/s | 4.1 |
| 2017 | 21.2°C | 16.4°C | 11.5°C | 25.8°C | 4.3°C | 72 mm | 86% | 0.5 m/s | 4 |
| 2016 | 19.6°C | 14.9°C | 10.2°C | 26.9°C | 2.8°C | 58 mm | 86% | 0.5 m/s | 4 |
| 2015 | 21.4°C | 16.5°C | 11.5°C | 26.9°C | 3.8°C | 177 mm | 85% | 0.5 m/s | 4.3 |
| 2014 | 19.0°C | 14.0°C | 9.1°C | 29.2°C | 2.0°C | 56 mm | 84% | 0.5 m/s | 4.2 |
| 2013 | 18.1°C | 13.7°C | 9.3°C | 23.5°C | 3.7°C | 126 mm | 88% | 0.5 m/s | 3.5 |
| 2012 | 19.0°C | 14.5°C | 10.0°C | 22.4°C | 3.2°C | 202 mm | 87% | 0.5 m/s | 3.6 |
| 2011 | 19.7°C | 15.3°C | 10.8°C | 24.4°C | 5.4°C | 34 mm | 86% | 0.5 m/s | 3.9 |
| 2010 | 19.0°C | 14.9°C | 10.8°C | 30.6°C | 5.4°C | 132 mm | 87% | 0.5 m/s | 3.3 |
| 2009 | 18.0°C | 13.0°C | 8.1°C | 24.3°C | 2.2°C | 80 mm | 85% | 0.5 m/s | 4.3 |
| 2008 | 18.2°C | 13.7°C | 9.2°C | 24.4°C | 1.2°C | 160 mm | 86% | 0.5 m/s | 3.9 |
| 2007 | 18.9°C | 14.0°C | 9.2°C | 25.4°C | 3.2°C | 72 mm | 82% | 0.5 m/s | 4.3 |
| 2006 | 18.7°C | 14.0°C | 9.4°C | 23.4°C | 4.8°C | 57 mm | 86% | 0.5 m/s | 4.1 |
| 2005 | 19.5°C | 15.1°C | 10.6°C | 24.8°C | 4.8°C | 93 mm | 85% | 0.5 m/s | 4 |
| 2004 | 18.2°C | 13.4°C | 8.5°C | 22.0°C | 5.0°C | 71 mm | 84% | 0.5 m/s | 4.2 |
| 2003 | 20.3°C | 15.5°C | 10.7°C | 26.0°C | 6.4°C | 69 mm | 85% | 0.5 m/s | 4.1 |
| 2002 | 19.5°C | 14.7°C | 9.9°C | 29.0°C | 2.6°C | 144 mm | 85% | 0.5 m/s | 3.7 |
| 2001 | 19.6°C | 14.5°C | 9.5°C | 26.3°C | 3.9°C | 73 mm | 82% | 0.5 m/s | 4.3 |
| 2000 | 17.6°C | 13.0°C | 8.4°C | 27.0°C | 0.9°C | 90 mm | 85% | 0.5 m/s | 3.9 |
| 1999 🔥 🌧️ | 21.6°C | 17.0°C | 12.3°C | 29.9°C | 5.7°C | 218 mm | 86% | 0.5 m/s | 3.8 |
| 1998 | 18.2°C | 13.9°C | 9.7°C | 24.1°C | 3.9°C | 120 mm | 86% | 0.5 m/s | 3.6 |
| 1997 | 17.8°C | 13.5°C | 9.2°C | 22.8°C | 2.8°C | 92 mm | 88% | 0.5 m/s | 3.3 |
| 1996 | 17.5°C | 13.6°C | 9.8°C | 26.5°C | 3.8°C | 149 mm | 87% | 0.6 m/s | 3.3 |
| 1995 | 17.3°C | 12.0°C | 6.6°C | 23.1°C | 0.3°C | 53 mm | 79% | 0.6 m/s | 4.3 |
| 1994 | 17.4°C | 13.0°C | 8.7°C | 22.4°C | 4.4°C | 67 mm | 85% | 0.5 m/s | 3.7 |
| 1993 | 18.2°C | 13.5°C | 8.9°C | 23.8°C | 2.2°C | 100 mm | 85% | 0.5 m/s | 3.8 |
| 1992 | 18.5°C | 13.6°C | 8.7°C | 23.5°C | 1.5°C | 52 mm | 85% | 0.5 m/s | 3.8 |
| 1991 | 17.2°C | 12.6°C | 8.0°C | 23.9°C | 0.6°C | 163 mm | 85% | 0.5 m/s | 3.8 |
| 1990 | 17.9°C | 13.4°C | 8.9°C | 24.4°C | 4.0°C | 106 mm | 86% | 0.5 m/s | 3.3 |
| 1989 | 18.2°C | 13.5°C | 8.7°C | 27.2°C | -1.3°C | 97 mm | 85% | 0.5 m/s | 4 |
| 1988 | 17.1°C | 12.5°C | 7.9°C | 23.4°C | 3.6°C | 71 mm | 84% | 0.6 m/s | 4 |
| 1987 | 17.4°C | 13.2°C | 9.0°C | 23.6°C | 0.1°C | 162 mm | 86% | 0.5 m/s | 3.6 |
| 1986 ❄️ | 16.4°C | 11.5°C | 6.5°C | 23.0°C | 1.5°C | 92 mm | 84% | 0.5 m/s | 3.8 |
| 1985 | 19.1°C | 14.1°C | 9.1°C | 25.8°C | 4.2°C | 47 mm | 84% | 0.5 m/s | 3.9 |
| 1984 | 17.1°C | 12.4°C | 7.6°C | 22.4°C | 1.6°C | 60 mm | 84% | 0.5 m/s | 4.3 |
| 1983 | 19.8°C | 14.8°C | 9.8°C | 26.6°C | 4.2°C | 56 mm | 85% | 0.5 m/s | — |
| 1982 | 18.5°C | 14.1°C | 9.7°C | 24.1°C | 6.3°C | 87 mm | 87% | 0.5 m/s | — |
| 1981 | 17.4°C | 13.1°C | 8.8°C | 22.6°C | 3.9°C | 122 mm | 85% | 0.6 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 18.8°C with lows near 9.5°C (mean 14.2°C), based on 45 years of NASA POWER data.
September averages 98 mm of rainfall in Saint John, about average for rainfall. The wettest on record was 218 mm in 1999.
The hottest September reached 30.6°C in 2010. The coldest dipped to -1.3°C in 1989.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2°C. Daytime highs moved from 18.4°C to 20.3°C and overnight lows from 9°C to 11°C over the same span.
September is one of the warmer months of the year in Saint John and about average for rainfall, so plan for around 18.8°C daytime highs and 9.5°C at night.
Not quite — September is the 9th coolest month in Saint John, averaging 14.2°C.
For September in Saint John, pack light layers you can adjust through the day, with typical highs of 18.8°C and lows of 9.5°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 85% — quite humid.
Average wind speed in September is 0.5 m/s. The windiest September on record averaged 0.6 m/s (1981).
The wettest September on record was 1999 with 218 mm. On average, September sees 98 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Saint John behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
