For those that haven't lived too long in Hawai`i the seasons are a subtle thing; it's generally always very warm during the day and warm at night all year round. In mid-winter the best advice is often to close a window or two to prevent those mid-60s temperatures from giving you a bit of a chill!
The same subtle change is often true at the summit of Mauna Kea although no day or night is warm, but there conditions can change a little more drastically. For instance, it's rare to get snow during the summer but watch out for those large snow drifts in January and February!
Bone-chilling night-time temperatures at this time of the year are usually the sign that we're into a new season, and boy was it cold the other night! There's no snow yet and we don't usually get much snowfall until December at the earliest. With this being an El Nino year, however, the chances of a lot of snow are reduced, but that doesn't stop the fairly marked drop in temperature at night, and you really feel it when the wind is blowing.
Or perhaps I'm just getting older...