Thing I would do is to wait unil it rains but somewhere you can still work on the engine (like 3/4 out of the garage, nose in) and try to duplicate (if not possible, I'd use a hose but might be related to humidity, not the water itself).
Might also wait until dark and look for sparks under the hood.
The real way is to go through the six page checklist in the factory service manual (a C engine manual is online a www.reatta.net
) . I agree it is probably electrical but this is the first I've heard of "a few cyl first, then all catch" since the days of distributers and carbs.
Just for *&G next time it won't start pull the air cleaner lid and see if there is a puddle inside.