The rainy season started in Okinawa on May 10th and is expected to last until June 21st. In the Kanto region where I live, it started June 7th and will likely continue until the third week of July.
You can see the expected rainy season forecast for regions of Japan and rainfall variation for the Kanto region - Another Rainy Season Arrives in Japan.
Yeah it started early this year... I wanted to do Ume (plum) syrup this year too with the fruits at my friends garden and the ume too where early. Usually you prepare the ume stuff (syrup, liquor or umeboshi) in the 2 first weeks of June in my area but this year I had the ume and sugar in the pot ready before May ended ^^;; do you think it's related to climate change? Also typhoons season started early this year 😱