I'm too late. Like a straggler from a flock of migrating geese, the odds now seem stacked against me from escaping the harsh winter of northern Japan.
My objective has become to "complete" Hokkaido by reaching its southwest corner, and then crossing the Tsugaru Strait back to Honshu. Looking at the map that doesn't seem a huge ask, but at this time of year the weather windows are at best short-lived and at other times a figment of wishful thinking.
In Japanese, "windsurfing" is called "windosurfing". That seems very apt right now.