Paul,
The main problem is that flights from the mainland run out of chemtrails before they get here.
I'll get back to you on contrails as it's an interesting subject on its own, but only if you want. Suffice it to say contrails have been present since we first learned how to fly. Chemtrails, on the other hand, have only existed since the internet started as anyone short of a tin-foil helmet and a laptop will tell you.
There are few flights over Hawaii so there are few contrails. Most inter-island flights don't get very high compared to the mainland, so the conditions that cause contrails don't exist so often. But some trans-Pacific flights do overfly the islands (US - Australia for instance) and I have seen the odd contrail at night, but it's rare.
Obviously the pilots have been told to shut down their chemtrails overnight, for whatever reason the conspirators will come up with. I can't think of a good one but am sure they will.
In addition, and I have to say I can't help thinking I'm helping out the fruitcakes here, Gemini, Keck and Subaru employ powerful lasers that they use to create a "guide star" that helps them correct for atmospheric conditions. (I'm told I shouldn't use the words "firing" or "shooting" lasers for fear of creating panic). The airlines and pilots know this and suspect they don't fly over the island to accommodate this.
And before anyone starts flapping their hands, these observatories are in contact with air traffic control and the lasers are shutdown whenever an aircraft gets close to the mountain.
Tom
http://apacificview.blogspot.com/