Situated close to central Japan, the climate of the Tokyo Islands is quite similar to say Tokyo and Yokohama. Being out in the ocean does make extremes, like storms and typhoons, more extreme. Weather can change quickly, for example a morning with lots of clouds can turn into bright sky when the wind picks up and even regional differences can relatively big due to the mountains; clouds gathered on one site of the volcano make it hard to see far ahead while you might be sunbathing on the other side, only kilometers away. Also, these are great diving destinations; under water the weather is not so important!
Winter, from December to February, is quite dry and sunny and the temperatures rarely drop below freezing. Snow falls only sporadically, most would be in February, a centimeter or 4 in all. Keep the wind in mind though, making for a high wind chill. Bringing windproofs is advisable but winter still makes for a good time to travel around the Tokyo Islands. Remember, there are always the hot springs to heat up in!
Spring is from March to May. Temperatures are warm but not too hot, plus there isn’t too much rain. The famous cherry blossoms are out during this time and there are festivals to enjoy. Oshima has a distinct type of blossom, transforming the whole island into white and green color. Spring is a great time to visit.
Summer begins in June and with the rest of the the country, the islands experience a three to four-week rainy season which is good for the crops. It is hot and humid during this time and temperatures are often in the mid 30’s celsius. But these being islands, the wind brings relief, especially at higher altitudes. Making summer on the islands much more pleasant then in a hot and sticky metropolis. Summer wraps up in August.
Autumn is from September to November and is characterised by light breezes and cooler temperatures of around 8-10ºC. Around November the leaves turn red, yellow and brown, especially the maple trees are stunning. Together with low visitor numbers and great temperatures this makes it an ideal time to plan your trip. Note that this is also the season with most typhoons which may cause havoc in your travel plans as ferries and flights might delay or even be suspended. October generally has most typhoons.