You can see Ni'ihau from a helicopter at least! The Northwestern Hawaiian Islands stretch 1200 miles northwest past Kauai, and they're remnants of old islands that have been mostly reclaimed by the ocean. Midway Island, famous for the WWII battle, is one of them. They're probably one of the hardest places on Earth to visit. Hope you're willing to dedicate the next several years of your life to becoming a marine biologist...

The main islands.

The Gay-Robinson family allowed you to go to Niihau?

The next week should get the trees really leafing out finally. The ECMWF also shows Tuesday - Saturday being mostly sunny. That period has slowly improved over the last few days. Also worth nothing the ECMWF AIFS is much more ridgy after day 8 than the operational run so maybe these temps will continue beyond the next week.

We have hiked on every island including Oahu... but never did Diamond Head. Too touristy I guess. Never been bothered by heat in Hawaii. But have been annoyed with it being too cool and windy many times in Hawaii.