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Monthly climate in Isumi, Japan

Last updated: July 31, 2025

Under the Köppen–Geiger climate classification Isumi features a humid subtropical climate (Cfa). Temperatures typically range between 9 °C (48 °F) and 27 °C (81 °F) through the year, but rarely can drop to 1 °C (35 °F) or can rise to as high as 31 °C (89 °F). The average annual precipitation amounts to about 1870 mm (73.6 inches) and receives 159 rainy days on the 1 mm (0.04 inches) threshold annually. Isumi enjoys an average of 2952 hours of sunshine throughout the year, and daylight varies from 9 hours 48 minutes to 14 hours 29 minutes per day.

Monthly average temperatures in Isumi, Japan

The warmest months in Isumi are July, August and September, with daily mean temperatures ranging from 25 to 27 °C (77 - 81 °F) throughout the day. The coldest temperatures usually occur in January, February and December, when daily mean temperatures range from 9 to 11 °C (48 - 53 °F) throughout the day. On average each year, Isumi experiences 69 days above 25 °C (77.0 °F) and 0 days below 0 °C (32.0 °F).

Monthly average temperatures with daily means, minimums and maximums for period, average high and low temperatures in Isumi. Generated using Copernicus Climate Change Service information. Data for period from January 2017 to June 2022.
 JanFebMarAprMayJunJulAugSepOctNovDec
Maximum19°C
(66°F)		18°C
(65°F)		19°C
(67°F)		21°C
(71°F)		25°C
(77°F)		27°C
(82°F)		31°C
(87°F)		31°C
(89°F)		31°C
(87°F)		27°C
(81°F)		23°C
(73°F)		21°C
(71°F)
Mean maximum16°C
(61°F)		16°C
(62°F)		18°C
(65°F)		20°C
(69°F)		24°C
(75°F)		25°C
(78°F)		29°C
(84°F)		31°C
(88°F)		29°C
(84°F)		26°C
(80°F)		22°C
(72°F)		19°C
(66°F)
Average high11°C
(51°F)		11°C
(52°F)		14°C
(57°F)		17°C
(62°F)		21°C
(69°F)		23°C
(74°F)		27°C
(80°F)		29°C
(84°F)		26°C
(79°F)		22°C
(72°F)		18°C
(65°F)		13°C
(56°F)
Daily mean9°C
(48°F)		9°C
(48°F)		12°C
(54°F)		15°C
(59°F)		19°C
(67°F)		22°C
(72°F)		25°C
(78°F)		27°C
(81°F)		25°C
(77°F)		21°C
(69°F)		16°C
(62°F)		11°C
(53°F)
Average low6°C
(44°F)		7°C
(44°F)		10°C
(50°F)		13°C
(56°F)		18°C
(64°F)		21°C
(69°F)		24°C
(76°F)		26°C
(79°F)		23°C
(74°F)		19°C
(67°F)		15°C
(59°F)		9°C
(49°F)
Mean minimum3°C
(38°F)		3°C
(37°F)		5°C
(42°F)		8°C
(46°F)		13°C
(56°F)		18°C
(65°F)		22°C
(71°F)		23°C
(73°F)		20°C
(68°F)		15°C
(59°F)		9°C
(49°F)		5°C
(41°F)
Minimum1°C
(35°F)		2°C
(35°F)		4°C
(40°F)		6°C
(43°F)		12°C
(55°F)		17°C
(63°F)		20°C
(68°F)		22°C
(72°F)		19°C
(66°F)		14°C
(57°F)		7°C
(45°F)		3°C
(37°F)

Compare climate in Isumi with other places

Compare temperature, precipitation, sunshine, UV index in Isumi, Japan with other places around the world.

Monthly average precipitation in Isumi, Japan

Isumi usually has the most precipitation in July, September and October, with an average of 16 rainy days and 238 mm (9.4 inches) of precipitation per month. The driest months in Isumi are January, February and August. On average, 86 mm (3.4 inches) of precipitation falls during these months.

Monthly average precipitation and precipitation days in Isumi. Generated using Copernicus Climate Change Service information. Data for period from January 2017 to January 2022.
 JanFebMarAprMayJunJulAugSepOctNovDec
Average precipitation mm (inches)77 (3.0)68 (2.7)180 (7.1)117 (4.6)140 (5.5)206 (8.1)206 (8.1)113 (4.5)214 (8.4)292 (11.5)142 (5.6)114 (4.5)
Average precipitation days (≥ 1 mm)81114111114161317171512

Monthly sunshine hours in Isumi, Japan

The sunniest months in Isumi are May, July and August, when the sun shines an average of 9 hours 21 minutes a day. Least sunny months in Isumi: January, October and December receive an average of 6 hours 34 minutes of sunshine daily.

Mean monthly sunshine duration, average sunshine hours per day and mean daily daylight hours in Isumi. Generated using Copernicus Atmosphere Monitoring Service information. Data for period from January 2017 to January 2022.
 JanFebMarAprMayJunJulAugSepOctNovDec
Mean monthly sunshine hours184218251271289267271309244211218216
Mean daily daylight hours10h 3m10h 53m11h 58m13h 5m14h 1m14h 29m14h 15m13h 26m12h 22m11h 15m10h 17m9h 48m

Solar UV radiation in Isumi, Japan

Isumi experiences the highest level of ultraviolet (UV) radiation in May, July and August, when the maximum UV index can reach values of 11 - 11, which corresponds to the Extreme category of sun exposure. January, February and December are in the Moderate exposure category. In these months, the maximum values of the UV index do not exceed 5. For more detailed information, check out our hourly Isumi UV Index data.

Average daily maximum UV levels by month for Isumi. Generated using Copernicus Atmosphere Monitoring Service information. Data for period from January 2022 to January 2023.
 JanFebMarAprMayJunJulAugSepOctNovDec
UV Index (month maximum)458101111111110754