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Iruma, Saitama Weather by Month and Climate Averages
Monthly normals · Rain · Snow
Sunshine · Freeze dates · Records · Best time to visit
What is the weather like in Iruma, Saitama?
Iruma, Saitama gets 1127 mm of precipitation a year over about 82 rainy days. August is the warmest month (average high 31°C) and January the coldest (average low -4°C).
Humid subtropical climate
Iruma, Saitama has hot summers and chilly winters. Daytime highs range from about 9°C in January to 31°C in August. September is usually the wettest month. The most comfortable time to visit is typically April to June and October, when daytime highs sit near 23°C.
| Season | Months | Avg low | Avg high |
|---|---|---|---|
| Winter | Dec–Feb | -3° | 10° |
| Spring | Mar–May | 6° | 19° |
| Summer | Jun–Aug | 19° | 29° |
| Autumn | Sep–Nov | 11° | 21° |
How much rain does Iruma get?
Iruma gets 1127 mm of precipitation in an average year, spread over about 82 days with measurable rain. That is fewer rainy days than 97% of Japan.
September is the wettest month, with 191 mm. February is the driest, with 27 mm. July has the most rainy days, about 11.
The longest dry spell in the last five years lasted 27 days, to January 12, 2024.
From October 2025 to September 2026 Iruma got 2910 mm of rain, against a normal of 1127 mm for those months. September 2026 had the most, with 1291 mm.
Iruma weather by month
Iruma weather in January
In January, Iruma averages a high of 9°C and a low of -4°C. It gets 35 mm of precipitation over about 3 rainy days. Estimated sunshine is 59% of daylight hours, derived from ERA5 cloud cover. The January record high is 19°C (1996) and the record low is -12°C (1970).
Iruma weather in February
In February, Iruma averages a high of 10°C and a low of -4°C. It gets 27 mm of precipitation over about 4 rainy days. Estimated sunshine is 56% of daylight hours, derived from ERA5 cloud cover. The February record high is 26°C (2009) and the record low is -12°C (1984).
Iruma weather in March
In March, Iruma averages a high of 13°C and a low of 0°C. It gets 56 mm of precipitation over about 6 rainy days. Estimated sunshine is 42% of daylight hours, derived from ERA5 cloud cover. The March record high is 27°C (2020) and the record low is -11°C (1977).
Iruma weather in April
In April, Iruma averages a high of 19°C and a low of 6°C. It gets 69 mm of precipitation over about 6 rainy days. Estimated sunshine is 38% of daylight hours, derived from ERA5 cloud cover. The April record high is 33°C (2004) and the record low is -4°C (1978). April is one of the most comfortable months to visit.
Iruma weather in May
In May, Iruma averages a high of 24°C and a low of 11°C. It gets 86 mm of precipitation over about 8 rainy days. Estimated sunshine is 28% of daylight hours, derived from ERA5 cloud cover. The May record high is 37°C (1993) and the record low is 1°C (1972). May is one of the most comfortable months to visit.
Iruma weather in June
In June, Iruma averages a high of 26°C and a low of 16°C. It gets 122 mm of precipitation over about 10 rainy days. Estimated sunshine is 19% of daylight hours, derived from ERA5 cloud cover. The June record high is 38°C (2011) and the record low is 6°C (1978). June is one of the most comfortable months to visit.
Iruma weather in July
In July, Iruma averages a high of 30°C and a low of 21°C. It gets 152 mm of precipitation over about 11 rainy days. Estimated sunshine is 23% of daylight hours, derived from ERA5 cloud cover. The July record high is 39°C (2018) and the record low is 9°C (1976).
Iruma weather in August
In August, Iruma averages a high of 31°C and a low of 21°C. It gets 141 mm of precipitation over about 8 rainy days. Estimated sunshine is 33% of daylight hours, derived from ERA5 cloud cover. The August record high is 39°C (1994) and the record low is 13°C (1976).
Iruma weather in September
In September, Iruma averages a high of 27°C and a low of 17°C. It gets 191 mm of precipitation over about 10 rainy days. Estimated sunshine is 26% of daylight hours, derived from ERA5 cloud cover. The September record high is 38°C (1984) and the record low is 7°C (1992).
Iruma weather in October
In October, Iruma averages a high of 21°C and a low of 11°C. It gets 175 mm of precipitation over about 8 rainy days. Estimated sunshine is 38% of daylight hours, derived from ERA5 cloud cover. The October record high is 32°C (2018) and the record low is 0°C (1971). October is one of the most comfortable months to visit.
Iruma weather in November
In November, Iruma averages a high of 16°C and a low of 3°C. It gets 43 mm of precipitation over about 5 rainy days. Estimated sunshine is 54% of daylight hours, derived from ERA5 cloud cover. The November record high is 26°C (2023) and the record low is -6°C (1973).
Iruma weather in December
In December, Iruma averages a high of 11°C and a low of -2°C. It gets 30 mm of precipitation over about 3 rainy days. Estimated sunshine is 66% of daylight hours, derived from ERA5 cloud cover. The December record high is 25°C (2004) and the record low is -12°C (1976).
Sunshine, humidity and wind in Iruma
December is the sunniest month in Iruma, with estimated sunshine of 66% of daylight hours from ERA5 cloud cover. June is the cloudiest, at 19%. The annual cloud-cover estimate is 40% of daylight hours; it is not a measurement of sunshine duration. Iruma is sunnier than 65% of Japan.
Humidity peaks in September at 83% and is lowest in February at 59%.
Iruma has about 29 days a year above 32°C. Iruma is hotter than 75% of Japan.
First and last freeze in Iruma
The first fall freeze in Iruma typically comes around November 16, and the last spring freeze around April 6. That leaves a frost-free growing season of about 224 days.
Iruma weather records
These records cover CHICHIBU during 1970–2026. Earlier records or other stations in the city may differ.
The hottest temperature on record at the Iruma station is 39°C, on August 7, 1994. The coldest is -12°C, on January 17, 1970.
The wettest day in the available station history brought 294 mm of precipitation, on September 12, 1982.
32 all-time records have been set at the station since 1970.
The best time to visit Iruma
The most comfortable time to visit is typically April to June and October, when daytime highs sit near 23°C.
Winter (December–February) is chilly, with average highs around 10°C and lows near -4°C.
Spring (March–May) is mild, with average highs around 19°C and lows near 5°C.
Summer (June–August) is hot, with average highs around 29°C and lows near 19°C. It can feel humid.
Autumn (September–November) is warm, with average highs around 21°C and lows near 10°C.
Monthly climate
| Month | Average low | Average high | Precip | Rain days | Humidity | Estimated sunshine | Record high | Record low |
|---|---|---|---|---|---|---|---|---|
| January | -4° | 9° | 35 mm | 3 | 61% | 59% | 19° | -12° |
| February | -4° | 10° | 27 mm | 4 | 59% | 56% | 26° | -12° |
| March | 0° | 13° | 56 mm | 6 | 65% | 42% | 27° | -11° |
| April | 6° | 19° | 69 mm | 6 | 68% | 38% | 33° | -4° |
| May | 11° | 24° | 86 mm | 8 | 73% | 28% | 37° | 1° |
| June | 16° | 26° | 122 mm | 10 | 80% | 19% | 38° | 6° |
| July | 21° | 30° | 152 mm | 11 | 82% | 23% | 39° | 9° |
| August | 21° | 31° | 141 mm | 8 | 81% | 33% | 39° | 13° |
| September | 17° | 27° | 191 mm | 10 | 83% | 26% | 38° | 7° |
| October | 11° | 21° | 175 mm | 8 | 77% | 38% | 32° | 0° |
| November | 3° | 16° | 43 mm | 5 | 72% | 54% | 26° | -6° |
| December | -2° | 11° | 30 mm | 3 | 64% | 66% | 25° | -12° |
Station: CHICHIBU, 33 km from the city. Temperature normal baseline: 1991–2020, calculated from available NOAA GHCN-Daily observations. Available station history: 1970–2026; record values refer to this station and period, not the entire city’s history. Precipitation includes rain and the water equivalent of frozen precipitation; snowfall depth is shown separately when available. Sources and methods
From ERA5 reanalysis. Sunshine is estimated from cloud cover.
Iruma climate questions
How much rain does Iruma get?
Iruma gets 1127 mm of precipitation in an average year, over about 82 rainy days.
What is the wettest month in Iruma?
September is the wettest month in Iruma, with 191 mm. February is the driest, with 27 mm.
How many rainy days does Iruma have a year?
Iruma has about 82 days with measurable rain in an average year. July has the most, about 11.
What is the hottest month in Iruma?
August is the warmest month in Iruma, with an average high of 31°C.
What is the coldest month in Iruma?
January is the coldest month in Iruma, with an average low of -4°C.
What is the record high temperature in Iruma?
Within the available 1970–2026 station history, the record high at the Iruma station is 39°C, set on August 7, 1994. The record low is -12°C, on January 17, 1970.
What is the sunniest month in Iruma?
December is the sunniest month in Iruma, with estimated sunshine of 66% of daylight hours from ERA5 cloud cover. June is the cloudiest.
When is the first frost in Iruma?
The first fall freeze in Iruma typically comes around November 16. The last spring freeze is around April 6.
What is the best time to visit Iruma?
The most comfortable time to visit is typically April to June and October, when daytime highs sit near 23°C.