weather will definitely effect boost.
what kind of boost controler you running? if you are runing 14psi, you dont even need a boost controler...with DP, intake, and exhaust most BPU supra hits 15-16 consistantly.
9psi is not normal at all...boost leak I would way.
most of the time its bad vacuum hose, sometimes when it heats up and expands it will start leaking boost, other times it hold in the vacuum....pull on every vacuum hose you can see, replace ones that comes off without giving a fight. a good vacuum hose should stick pretty good, I usually need to use a poker to get it off..or twist it hard several times.