Hawaii's heaviest rains are come from winter storms between October and April. While the effects of terrain on storm rainfall are not as great as on trade wind showers, large differences over small distances do occur, because of topography and location of the rain clouds.
Which Hawaii Island gets least rain?
The driest part of the Hawaiian islands is the northwest coast of the Big Island, in the shadow of the big mountains, which gets less rain from the Kona storms that can come up from the south in winter, and almost no rain from the tradewinds in the summer, because it's in the rain shadow.