Climate - Southern Islands (Japan)

To the south of the main islands of Japan, we find some archipelagos made up of smaller islands. Generally, these islands have a subtropical climate, with mild winters and hot, muggy summers. The rains are abundant and well distributed throughout the year.

Ryukyu

---

To the south of Kyushu we find the Ryukyu Islands, in turn divided into different groups, which almost reach the Tropic, to the east of Taiwan.

Osumi

In the northernmost group of islands (Osumi), the winter is mild, with an average in January of 11/12 °C (51/54 °F), but it's also rainy and subject to cold winds from the north-west. The main islands of the group are Yakushima, Tanegashima and Kuchinoerabu-jima. Here are the average temperatures of Yakushima.

The rains are particularly abundant, especially on the island of Yakushima, whose central mountain is one of the rainiest places in the world. On the coast, 4,650 millimeters (184 inches) of rain fall per year at Yakushima and 2,500 mm (100 in) at Tanegashima. Here is the average rainfall in Yakushima.

On these islands, the sea is cool in winter, it is warm enough for swimming (with a temperature equal to or higher than 23 °C or 73 °F) from May to November, and it becomes pleasantly warm from July to September.

Proceeding to the south (Tokara and Amami islands), the winter gradually becomes milder.
On the southernmost islands (Okinawa, Miyako - see Miyakojima, and Yaeyama - see Ishigaki), the winter is so mild as to have a spring-like flavor, even though the rains are quite abundant.
In Okinawa, where the climate is almost tropical, the average in January is around 17 °C (63 °F). Here it never freezes or snows. Here are the average temperatures of Naha.

In Okinawa, 2,000 mm (80 in) of rain fall per year, with a maximum in the period from May to September (but in which there is a decrease in July) and a relative minimum in winter, of about 100 mm (4 in) per month. Here is the average precipitation.

The sea in Okinawa is never cold, in fact the water temperature reaches a minimum of 22 °C (72 °F) in February and March, when it is quite cool, while it becomes very warm in summer.

Outside of this group, to the south-east of Okinawa we find the Daito Islands, which have a climate similar to that of Okinawa, although a little less rainy: in Minamidaito the rains amount to 1,600 mm (63 in) per year.

Izu

---

Further east, in the part of the Pacific Ocean to the south of Tokyo (Philippine Sea), we find the Izu Islands (also called Tokyo Islands), which are very rainy (though not as rainy as Yakushima). In Hachijo-jima, rainfall amounts to as much as 3,000 mm (121 in) per year. However, winter is the least rainy season.
The temperature becomes progressively milder as we move south: in Izu Oshima it is still similar to that of the south coast of Honshu, and in fact the January average is 7 °C (45 °F). Here are the average temperatures of Izu-Oshima.

Further south, the January average rises to 9.5 °C (49 °F) in Miyake-jima, to 10.5 °C (51 °F) in Hachijo-jima, and to 14 °C (57 °F) in Tori-shima. The island of Nii-jima is located between Izu-Oshima and Miyake-jima.
Here are the average temperatures of Miyake-jima.

Ogasawara

To the south of the Izus we find the Ogasawara islands or Bonin, which also stretch almost to the Tropic, but they are not as rainy as the Ryukyus: at Chichi-jima and Iwo-jima the rainfall amounts to 1.300 mm (51 in) per year, and in Minamitori-jima to just 1.000 mm (40 in).
Here is the average rainfall in Chichi-jima. Here too, in July there is a relative decrease in the rains.

In Chichi-jima, the temperatures are similar to those of Okinawa.

The sunniest month in Chichi-jima is July.

Typhoons

---

The southern islands of Japan can be affected by typhoons, the tropical cyclones of the western Pacific. Actually, these islands are often hit harder than Japan's main islands.
Typically, typhoons occur from June to October. Occasionally they have also occurred before and after this period (so, from late April to late May, and from early November to early December). However, they are more frequent from August to early October.