Climate averages 1991–2020
Iruma weather
in September.
A warm, very wet month: the 3rd warmest and the wettest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in Iruma: daytime highs average 25.0°C and nights cool to about 18.6°C. By daytime temperature it is the 3rd warmest of the 12 months.
Expect about 249 mm of rain on roughly 18 days, which makes September a very wet month (the wettest month of the year). Daylight, from sunrise to sunset, lasts about 12 h 26 min on an average September day.
The nearest other city in this atlas is Sayama (6 km away). In September its highs average 25.3°C, about as warm as Iruma, with 204 mm of rain.
Among the 303 cities listed in Japan, Iruma ranks joint 222nd of 303 for the warmest September highs and joint 279th of 303 for the driest September (rainfall, lowest first). The mean September high of those 303 cities is 25.7°C; Iruma is 0.7°C cooler than that mean.
From September to October, average highs fall by 5.4°C to 19.6°C, and monthly rainfall falls from 249 mm to 242 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Iruma climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 7.2°C-2.7°C | -2.7°C | 77 | 8.5 | 10.010 h |
| February | 8.1°C-2.0°C | -2.0°C | 76 | 9.7 | 10.911 h |
| March | 11.7°C1.5°C | 1.5°C | 139 | 15.2 | 11.912 h |
| April | 16.8°C6.8°C | 6.8°C | 146 | 14.6 | 13.113 h |
| May | 21.2°C12.3°C | 12.3°C | 166 | 15.6 | 14.014 h |
| June | 23.8°C16.7°C | 16.7°C | 222 | 19.5 | 14.515 h |
| July | 27.5°C20.9°C | 20.9°C | 243 | 21.8 | 14.314 h |
| August | 28.7°C22.2°C | 22.2°C | 205 | 21.0 | 13.514 h |
| September, selected | 25.0°C18.6°C | 18.6°C | 249 | 18.2 | 12.412 h |
| October | 19.6°C12.6°C | 12.6°C | 242 | 16.2 | 11.311 h |
| November | 14.6°C6.3°C | 6.3°C | 101 | 11.3 | 10.310 h |
| December | 9.7°C0.4°C | 0.4°C | 68 | 8.3 | 9.810 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Sayama in SeptemberJapan · 6 kmHigh 25.3°C · Low 18.8°C · 204 mm rain
- Hannō in SeptemberJapan · 6 kmHigh 25.5°C · Low 19.2°C · 249 mm rain
- Tokorozawa in SeptemberJapan · 9 kmHigh 25.2°C · Low 18.9°C · 204 mm rain
- Ōme in SeptemberJapan · 12 kmHigh 25.3°C · Low 19.0°C · 249 mm rain
- Kawagoe in SeptemberJapan · 15 kmHigh 25.6°C · Low 19.0°C · 186 mm rain
- Sakado in SeptemberJapan · 16 kmHigh 25.7°C · Low 19.2°C · 186 mm rain
- Akiruno in SeptemberJapan · 16 kmHigh 25.3°C · Low 19.0°C · 249 mm rain
- Hino in SeptemberJapan · 16 kmHigh 25.1°C · Low 19.0°C · 204 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Iruma) is explained once on the Iruma year overview and on the Sources, method and limits page.
Hachiōji, Ōme and Akiruno lie in the same rainfall cell, so their rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.