Hawaii’s air temperature does not stray too far year-round with lows on average (in the colder months) in the mid-60s and highs on average (in the warmer months) in the upper 80s.
The air temperature in late June/early July typically has lows in the mid-70s with highs in the mid to high 80s, with partially cloudy skies expected from time to time, and low (roughly 20% or less) chances of rain. The water temperature is expected mid to high 70s (75-80 degrees). Late June sunrises are just before 6 am HST and sunset is just after 7 pm HST.
We suggest bringing plenty of REEF SAFE sunscreen if you plan to be in the ocean as there is a healthy marine life population along the Kohala Coast. If you’re staying at the Mauna Lani, there is also backup sunscreen available at the pools (and in the Goop Store on the property - although it won’t be cheap at the Goop Store - please blame Gwen).
Note, if you plan to visit Hilo, Mauna Kea or any of the other volcanos, the weather is much chillier at the higher elevations (there is snow on Mauna Kea much of the year) so you should pack accordingly if your plans will bring you to the higher elevations.