I actually posted a similar post about one of my JWP having needle discoloration, only mine is actually black at the tips. I sprayed it an Ortho fungicide and the browning/discoloration stopped spreading. Look closely at next year's buds at the terminals and the base of the needles, are they green?
I know a great authority on JWP, Julian Adams who's the only individual in the country who specializes in Zuisho JWP air layers and Ishizuchi JWP seedling, and sells them at a great price...fyi. He's based in VA which is also very humid for most of the year. I discussed the issue with him and he said that as long as next year's buds at the terminals are healthy you have nothing to worry about. Also if the BASE of the needles are still green the tree will be fine. The tree is investing all it's energy into next year's buds so even if this year's foliage looks unhealthy, it's not nearly as serious as having unhealthy buds, or God forbid, no buds at all!!
Despite what many bonsaiists say about JWP being finicky, Julian and myself both agree that they're tough plants.