You'll likely spend much of your trip indoors, but if you want to see more of the area, taking a look at local weather data can help you. The hottest months are usually August and September with an average temp of 76°F, while the coldest months are February and January with an average of 72°F. The rainiest months in Kailua-Kona are August, June, July, and May, with each month seeing an average of 11 inches of rainfall.