If you're in a closed shop can you borrow/rent a dehumidifier? Here's a previous thread that may help..  http://www.clcboats.com/forum/clcforum/thread/15807.html

 As an alternative I would think a two part such as Interlux Epoxy Primekote would do well.

I don't have an exact answer to your primary question, but suggest you go to one of the better local weather sites that shows a graph of current and projected conditions,  Look for the relative humidity curve.  Right now in the DC area the relative humidity is above 90 %.  Watch for times when the humidity is projected to be lower and prime away.  There are low humidity times during some summer days.  What you really want to avoid are times when the local temperature is close to or below the dew point temperature.  That's when you can can have moisture condense on your hull and really spoil things.  Apply paint and primer when the temps are at least 5 or more degrees above the dew point temp.  Added insurance against humidity would be to use a good dehumidifier in your work area or work in air conditioned spaces.

You should be sanding most of the primer off anyway, so don't get stressed over the primer.  Good luck.

System 3 Yacht Primer doesn't care about humidity (and the paint actually works better in high humidity). I've been pinging CLC to carry the stuff for a few years now, but John says there's not enough demand. So either join me in pinging them or buy it directly from S3.

Laszlo