Climate - Yakushima (Japan)

The climate of the island of Yakushima is humid subtropical, with mild winters and hot, muggy summers, and it's famous in Japan for being rain-soaked all year round.
The island is located at the 30th parallel, south of Kyushu, and together with other islands such as Tanegashima, Kuchinoerabu-jima, Kuroshima, and Iojima, is part of the Osumi islands, the northernmost of the Ryukyus. In winter, it is affected by weather disturbances due to the clash between cold air masses coming from the Asian continent and mild and moist air masses that lie on the East China Sea. In summer, there are periods of bad weather due to the summer monsoon, as well as to typhoons.
The temperatures are similar to those of Mediterranean islands such as Sicily. In winter, the temperature never drops below freezing, but there may be cold periods, during which highs drop below 10 °C (50 °F), the wind blows, and lows approach 0°C (32 °F). Sometimes it can even snow.
In summer, hot and sticky weather prevails, although sea breezes blow.
Here are the average temperatures.

As mentioned, precipitation is very abundant: on the coast, more than 4 meters and a half (14 feet) of rain fall per year, of which 860 millimeters (34 inches) fall in June, the wettest month. Here is the average precipitation.

In the interior of the island, on the slopes of Mount Miyanoura-dake, 1,936 meters (6,351 feet) high, the situation is even worse, since precipitation reaches 10 meters (33 feet): so, this is one of the rainiest places in the world. On the mountain, a famous forest is found, visited by many tourists and protected by UNESCO; it hosts ancient cedars, the most famous of which is called Jomon Sugi, which is 25 meters (82 feet) high and is thought to be at least 2,000 years old. The tree is located at 1,300 meters (4,300 feet) above sea level.
In winter, the mountain can be covered with snow. On the top, the temperature is on average 11.5 degrees Celsius (20.5 °F) lower than in the plain (and the difference becomes even greater during outbreaks of cold air).



The amount of sunshine in Yakushima is scarce in winter, when cloudy skies prevail, it is mediocre in spring and autumn, while it is decent in July and August, at least on the coast, when the rains are still abundant, but they are not so frequent, and there are 6.5/7 hours of sunshine per day. Here are the average sunshine hours per day.

The sea in Yakushima is cool in winter, but not impossible for a swim. It's warm enough for swimming, with a temperature equal to or higher than 23 °C (73 °F) from May to November, and it becomes pleasantly warm from July to September. Here are the average sea temperatures.

As mentioned, in summer and early autumn, from June to October (and more likely from August to early October), Yakushima can be affected by typhoons, the tropical cyclones of Southeast Asia.

Best Time

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It is difficult to find the best time to visit Yakushima, because there is no dry and sunny period. In addition, in winter it can get cold, while in summer and autumn, tropical cyclones can pass.
In July and August, the sunniest months, there is humid heat at sea level, but the temperature is milder in the mountains.
At sea level, the mildest temperatures are recorded in April-May and from early October to mid-November.

Yakushima - Weather by month

Based on the period 1991-2020

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In January, the coldest month of the year, the weather in Yakushima is usually mild. The average temperature is of 11.6 °C (53 °F), with a minimum of 8.6 °C (47.6 °F) and a maximum of 14.6 °C (58.3 °F).
On the coldest nights of the month, the temperature usually drops to around 4.5 °C (39.5 °F). However, it dropped to 1 °C (33.8 °F) in January 2016.
On the warmest days of the month, the temperature usually reaches around 21 °C (70 °F). However, it reached 25 °C (77 °F) in January 1991.
Precipitation amounts to 295 mm (11.6 in), distributed over 17 days.
The day lasts on average 10 hours and 25 minutes.
There are on average 2.5 hours of sunshine per day. So, the sun shines 23% of the time.
The average humidity is 67%.
The average wind speed is 21 kph (13 mph).
The average sea temperature is of 20 °C (68 °F). Therefore, the sea is very cool for swimming.

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In February, the weather in Yakushima is usually mild. The average temperature is of 12.1 °C (54 °F), with a minimum of 8.9 °C (48 °F) and a maximum of 15.4 °C (59.7 °F).
On the coldest nights of the month, the temperature usually drops to around 5 °C (40.5 °F). However, it dropped to 1.7 °C (35.1 °F) in February 2018.
On the warmest days of the month, the temperature usually reaches around 22 °C (72 °F). However, it reached 25.6 °C (78.1 °F) in February 2010.
Precipitation amounts to 290 mm (11.4 in), distributed over 15 days.
The day lasts on average 11 hours and 5 minutes.
There are on average 3 hours of sunshine per day. So, the sun shines 27% of the time.
The average humidity is 68%.
The average wind speed is 21 kph (13 mph).
The average sea temperature is of 19.5 °C (67 °F). Therefore, the sea is very cool for swimming.

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In March, the weather in Yakushima is usually mild. The average temperature is of 14.4 °C (58 °F), with a minimum of 10.9 °C (51.7 °F) and a maximum of 17.9 °C (64.2 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 6 °C (43 °F). However, it dropped to 1.5 °C (34.7 °F) in March 2005.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 24 °C (75.5 °F). However, it reached 27.9 °C (82.2 °F) in March 2007.
Precipitation amounts to 385 mm (15.2 in), distributed over 16 days.
The day lasts on average 12 hours and 0 minutes.
There are on average 4 hours of sunshine per day. So, the sun shines 32% of the time.
The average humidity is 68%.
The average wind speed is 19 kph (12 mph).
The average sea temperature is of 20 °C (67.5 °F). Therefore, the sea is very cool for swimming.

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In April, the weather in Yakushima is usually very mild. The average temperature is of 17.6 °C (64 °F), with a minimum of 13.9 °C (57 °F) and a maximum of 21.3 °C (70.4 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 9 °C (48.5 °F). However, it dropped to 6.1 °C (43 °F) in April 1993.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 26 °C (78.5 °F). However, it reached 28.7 °C (83.7 °F) in April 2003.
Precipitation amounts to 405 mm (15.9 in), distributed over 14 days.
The day lasts on average 12 hours and 55 minutes.
There are on average 5 hours of sunshine per day. So, the sun shines 38% of the time.
The average humidity is 70%. Hence, the air is normally humid.
The average wind speed is 17 kph (11 mph).
The average sea temperature is of 21 °C (70 °F). Therefore, the sea is cool for swimming.

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In May, the weather in Yakushima is usually warm. The average temperature is of 20.8 °C (70 °F), with a minimum of 17.2 °C (62.9 °F) and a maximum of 24.5 °C (76.1 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 13 °C (55 °F). However, it dropped to 10.5 °C (50.9 °F) in May 2010.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 28.5 °C (83.5 °F). However, it reached 32 °C (89.6 °F) in May 2004.
Precipitation amounts to 445 mm (17.5 in), distributed over 14 days.
The day lasts on average 13 hours and 40 minutes.
There are on average 5 hours of sunshine per day. So, the sun shines 36% of the time.
The average humidity is 75%. Hence, the air is normally humid.
The average wind speed is 15 kph (9 mph).
The average sea temperature is of 23.5 °C (74.5 °F). Therefore, the sea can be considered barely acceptable for swimming.

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In June, the weather in Yakushima is usually warm to hot and muggy. The average temperature is of 23.9 °C (75 °F), with a minimum of 20.8 °C (69.5 °F) and a maximum of 26.9 °C (80.5 °F).
On the coldest nights, the temperature usually drops to around 17 °C (62.5 °F). However, it dropped to 13.8 °C (56.8 °F) in June 1993.
On the warmest days, the temperature usually reaches around 32 °C (89.5 °F). However, it reached 35 °C (95 °F) in June 2007.
Precipitation amounts to 860 mm (33.9 in), distributed over 20 days.
The day lasts on average 14 hours and 5 minutes. So the days are long. June 21, the summer solstice, is the longest day of the year in the Northern Hemisphere.
There are on average 3.5 hours of sunshine per day. So, the sun shines 24% of the time.
The average humidity is 84%. Hence, the air is normally humid.
The average wind speed is 12 kph (7 mph).
The average sea temperature is of 25 °C (77.5 °F). Therefore, the sea is warm enough for swimming.

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In July, the weather in Yakushima is usually warm to hot and muggy. The average temperature is of 27.1 °C (81 °F), with a minimum of 23.8 °C (74.8 °F) and a maximum of 30.5 °C (86.8 °F).
On the coldest nights of the month, the temperature usually drops to around 21.5 °C (70.5 °F). However, it dropped to 19 °C (66.2 °F) in July 2009.
On the warmest days of the month, the temperature usually reaches around 33 °C (91.5 °F). However, it reached 35.1 °C (95.2 °F) in July 2005.
Precipitation amounts to 360 mm (14.2 in), distributed over 12 days.
The day lasts on average 13 hours and 55 minutes.
There are on average 7 hours of sunshine per day. So, the sun shines 49% of the time.
The average humidity is 82%. Hence, the air is normally humid.
The average wind speed is 11 kph (7 mph).
The average sea temperature is of 27.5 °C (81.5 °F). Therefore, the sea is pleasantly warm and allows long swims.

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In August, the hottest month of the year, the weather in Yakushima is usually very hot and muggy. The average temperature is of 27.7 °C (82 °F), with a minimum of 24.4 °C (76 °F) and a maximum of 30.9 °C (87.6 °F).
On the coldest nights of the month, the temperature usually drops to around 22 °C (71.5 °F). However, it dropped to 20.1 °C (68.2 °F) in August 2002.
On the warmest days of the month, the temperature usually reaches around 33 °C (92 °F). However, it reached 35.4 °C (95.7 °F) in August 2006.
Precipitation amounts to 255 mm (10 in), distributed over 15 days.
The day lasts on average 13 hours and 10 minutes.
There are on average 6.5 hours of sunshine per day. So, the sun shines 49% of the time.
The average humidity is 81%. Hence, the air is normally humid.
The average wind speed is 13 kph (8 mph).
The average sea temperature is of 28.5 °C (83 °F). Therefore, the sea is pleasantly warm and allows long swims.

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In September, the weather in Yakushima is usually warm to hot and muggy. The average temperature is of 25.7 °C (78 °F), with a minimum of 22.6 °C (72.8 °F) and a maximum of 28.8 °C (83.9 °F).
On the coldest nights, the temperature usually drops to around 19 °C (66 °F). However, it dropped to 13 °C (55.4 °F) in September 1991.
On the warmest days, the temperature usually reaches around 31.5 °C (89 °F). However, it reached 34.7 °C (94.5 °F) in September 1995.
Precipitation amounts to 450 mm (17.7 in), distributed over 16 days.
The day lasts on average 12 hours and 20 minutes.
There are on average 4.5 hours of sunshine per day. So, the sun shines 38% of the time.
The average humidity is 80%. Hence, the air is normally humid.
The average wind speed is 14 kph (9 mph).
The average sea temperature is of 27.5 °C (81.5 °F). Therefore, the sea is pleasantly warm and allows long swims.

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In October, the weather in Yakushima is usually warm. The average temperature is of 22.2 °C (72 °F), with a minimum of 19.1 °C (66.5 °F) and a maximum of 25.2 °C (77.4 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 14.5 °C (58.5 °F). However, it dropped to 11.1 °C (52 °F) in October 1997.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 29 °C (84.5 °F). However, it reached 31.3 °C (88.3 °F) in October 2015.
Precipitation amounts to 310 mm (12.2 in), distributed over 13 days.
The day lasts on average 11 hours and 25 minutes.
There are on average 3.5 hours of sunshine per day. So, the sun shines 33% of the time.
The average humidity is 74%. Hence, the air is normally humid.
The average wind speed is 17 kph (11 mph).
The average sea temperature is of 26 °C (79 °F). Therefore, the sea is warm enough for swimming.

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In November, the weather in Yakushima is usually very mild. The average temperature is of 18.0 °C (64 °F), with a minimum of 14.9 °C (58.9 °F) and a maximum of 21.1 °C (70 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 10 °C (50 °F). However, it dropped to 7.2 °C (45 °F) in November 2013.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 26 °C (78.5 °F). However, it reached 30.7 °C (87.3 °F) in November 2000.
Precipitation amounts to 310 mm (12.2 in), distributed over 13 days.
The day lasts on average 10 hours and 35 minutes.
There are on average 3 hours of sunshine per day. So, the sun shines 31% of the time.
The average humidity is 70%. Hence, the air is normally humid.
The average wind speed is 17 kph (11 mph).
The average sea temperature is of 24 °C (75 °F). Therefore, the sea is warm enough for swimming.

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In December, the weather in Yakushima is usually mild. The average temperature is of 13.7 °C (57 °F), with a minimum of 10.6 °C (51.2 °F) and a maximum of 16.7 °C (62 °F).
On the coldest nights of the month, the temperature usually drops to around 6 °C (42.5 °F). However, it dropped to 2.4 °C (36.3 °F) in December 2010.
On the warmest days of the month, the temperature usually reaches around 22.5 °C (72.5 °F). However, it reached 26.6 °C (79.9 °F) in December 2018.
Precipitation amounts to 280 mm (11 in), distributed over 16 days.
The day lasts on average 10 hours and 10 minutes. December 21, the winter solstice, is the shortest day of the year in the Northern Hemisphere.
There are on average 2.5 hours of sunshine per day. So, the sun shines 25% of the time.
The average humidity is 68%.
The average wind speed is 20 kph (12 mph).
The average sea temperature is of 21.5 °C (70.5 °F). Therefore, the sea is cool for swimming.