Hawaiian weather causes a lot of confusion for the uninitiated. In most travel destinations, the higher the hotel and air rates, the better the weather. That's not the case in Hawaii. American school holidays and Japan's Golden Week, typically from the end of April to the first week of May determine the levels.
Basically Hawaii is two seasons, Summer and Winter. While the temperature is pleasant year round, it does get warmer in the summer. Winter brings rainfall, though it is unlikely your vacation will be a washout. Hurricanes are a rarity in Hawaii due to atmospheric conditions and trade winds. Keep in mind that the Hawaiian islands are the only significant land mass in the 2500 mile stretch of Pacific from California. So Hawaii contains many microclimates.
The following link is the best I've found charting the variations in Hawaiian weather. But throwing climate change and Mother Nature into the mix, there are no guarantees.
For Hawaiian weather charts and comparisons for all the islands CLICK HERE.