Climates vary a lot as you travel around the Big Island. Rainfall, for example, varies from under ten inches a year (desert) to over 300 inches a year (rainforest). The map will give you an idea for the wet and dry areas of the island.
Many of our microclimates are the result of changes of altitude. The higher altitudes of Volcano Village and Waimea can give visitors a respite from the heat of lower altitudes, but the temperature can drop into the 40s and 50s, surprising those who are not dressed for cool temperatures. A sweatshirt and long pants are always good to have on the island, just in case!
Wind is another variable to be considered. Tradewinds typically come out of the northeast, bringing moisture. Not surprisingly, the northeast side of the island has a lot of rainfall, which produces streams, waterfalls and lush vegetation.
The five mountains that comprise the Big Island partially block this flow of moist air, creating dry parts of the Big Island.
Occasionally, wind patterns shift and the "Kona Winds" come out of the south bringing stormy weather to the drier parts of the island.
Finally, keep in mind that there are four areas of the Big Island that are very often windy - North Kohala, South Point, Waimea, and the Saddle Road (including the high altitude Maunakea).