The weather is pretty consistent at all times in Kihei. It receives the least rainfall in all of Maui. There is no best time to visit Kihei as such in terms of weather. It is just that you should be avoiding summer vacations, thanksgiving and Christmas week because finding reservations at this time is next to impossible.
But if you want to visit Kihei to mix with people and have a lot of fun, then June is the best time as there are annual events happening at this time. Apart from that the weather averages for the months do not fluctuate too much.
From December to April, the lowest it goes to is 16 degree Celsius and goes up to 28 degree Celsius. May to October , the temperature gets a little warm with the minimum being 20 degree Celsius and maximum going as high as 30 degree Celsius. The month of November is the most pleasant of them all fluctuating between 20 degrees Celsius to 26 degrees Celsius.
The highest rainfall is experienced in the months of January, March and December where even the precipitation is the highest and even the number of days experiencing rainfall increase in number.