The national roads serving the island are the Route 266 and Route 324 Kamishima Island is located in the humid subtropical climate zone (Köppen Cfa), with four distinct seasons.

Winters tend to be sunny, windy, and relatively dry; snow falls occasionally in the higher elevations, but seldom near sea level.

Spring in Kamishima Island starts off mild, but ends up being hot and humid.

The summer tends to be Kamishima's wettest season, with the tsuyu (梅雨, tsuyu, "plum rain") — the rainy season — occurring between early June (average: June 7) to late July (average: July 21).

The island's weather is affected by the nearby Liman current [ja] while being shielded from the warm Kuroshio Current off the coast of Kyushu island, resulting in a wetter and colder climate than should be expected at those latitudes.