I lived on Oahu for 4 years. I've literally done it all there, from jungle, conifer, and mountain peak hiking and camping on most of the islands to scuba diving, snorkeling, kayaking and boogey boarding.
Depending on the elevation, time of year, and coastal breezes, you'll experience anything from 65 degrees to 89 degrees in the daytime and 65 degrees to 30 degrees at night.
Your biggest concern will be keeping dry since the forested interior of all the islands get lots of rain. I've spent 3 weeks in the Kahuku Mountain Range on Oahu were it rained 24 hours a day. I've also on rare occasions such as on Molokai spent 4 days with no rain. On the Big Island (Hawaii) I've had 30 degree consecutive nights.
The issue you'll probably have the most is dealing with the cool breeze coming off the ocean when you're wet from rain.
List your details as closely as you can and I'll be able to offer very experienced advice.