I was in Hilo on the Big Island once for 5 days, and it felt like it rained non-stop. Heavy rain too - SE Asian monsoon type stuff
About five or six years ago we stayed over on the dry side north of Kona. Drove up to Wiamea and down the northeast coast road to Hilo. Just for the day. We had lunch in downtown Hilo. We also went to some big waterfall right outside of Hilo. They had umbrellas to use for the walk through the park to the river.
On the north side of Hilo we drove through a rain storm where I wished that the wiper blades had another speed above high. Like hyper drive wiper speed. It came down in buckets. A local told me it happens all the time. Why do you think its so green over here?