What kind of hunt? Spot and stalk, over bait, I am assuming not over hounds.
I also have two separate 5 day hunts coming up that my oldest Son and I have been doing (still waiting for my rug to be done from last springs hunt).
Hunting over bait usually involves being in some sort of cover. Big timber or the like and rain does not seem to bother them as bad.
For spot and stock, As stated above right after a rain or thunder shower can be real good but will likely be slow during. Just a steady light drizzle don't seen to bother them as bad.
Get a good light weight small tarp that you can stake out (don't forget the stakes and guy lines) and us as shelter to sit and glass from. During a rain really watch the "edges" of the openings. Especially if it is larger timbers edges. The Bears will hang out in there under the canopy of trees and feed on grasses that are encroaching into the trees while waiting for the rain to stop. Or they just lay up right at edges and nap.
Regardless of rain (outside of a flat out deluge) I would be sure to have my rain gear a light wait tarp and just hunt.
Be well, shoot well,
Dan