Japan's rainy season (梅雨, tsuyu) officially arrived today! It's actually been a long time coming, as I was expecting it at the very beginning of June, but it's taken until the 14th to arrive in Tokyo.
Rainy season in Japan is caused by cold northerly air masses meeting warm air from the south, which creates a stable front across Japan, bringing clouds and rain. The average rainy season in Tokyo lasts from 8th June until 20th July, which seems like a long time for it to rain! But it doesn't rain every day, and I read an information page that said that Tokyo records an average of 12 days of rain in June, and 120 hours of sunshine. But this fluctuates from year to year. Okinawa (沖縄) and the other southern islands get rainy season from the beginning of May until about the 23rd June, so it's much earlier, and then it spreads north from there. But Japan's northernmost island, Hokkaido (北海道, Hokkaidou) hardly sees any of the rain because of the northerly latitude. So lucky!
I remember the rainy season two years ago, in 2008, was quite short and not very intense. It arrived earlier than usual, and I recall it only lasted about three weeks. It was actually quite comfortable, keeping the heat down, and the misty drizzle made me very nostalgic of Britain. But it was very humid, and on the days when the temperature rose, it was very sticky and uncomfortable! The humidity seems to average about 95% in rainy season, but there were plenty of days when 100% was recorded.
This year so far the humidity has only started to worsen over the past week or so. Up until then it was gorgeous sun and clear blue skies, but now it's getting to the time when you walk home at night in sandals and shorts and see moisture dancing in car headlights.
The next week's weather forecast is mainly for cloud or light rain, with temperatures hovering around 28C, but today is only 19C, so it's being kind and easing us in slowly. Thursday is going to be a bit of a killer, with predictions of 31C and cloud. That's going to be a very humid day!
It's a shame because from now until I leave rainy season will be in full swing, so my immediate memory of Japan will be cloud and mist! But it might mean Britain is a relief from the rain! (Which I don't think I've ever said before...)
There's more information about the dates tsuyu starts and ends on the Japan Meteorological Agency website.