Like Precise said, check the ECU see if there is anything stored. It might help figure out what the issue is.
Do you have a lower skid plate and are the rubber side skirts in the front fenders intact?
I suspect the cause will be water in the engine bay splashing up on something more than undernearth teh chassis.
I am thinking its water on the distributor cap. Some caps have a breather on them and water can get in (been there) or poor seals around the base allowing some moisture inside.
If you pop your distrubutor cap I would not be surprised if there was condensation inside, which can cause some arching inside the cap. ON a non-humid day I would get a can of wire dryer, http://crcindustries.com/auto/?s=05104 its about $3 for a can and spray the inside of the cap, let it dry and then use a small amount of white lithium grease on the lip of the cap and re-attach it to the distributor. A small amount of dielectric grease on the cap would be ok too.
ALSO
the spark plug wires have DEEP galleries that water (and other crap) can fill up with. The heat of the motor will evaporate the water but it can play hell with the spark plugs making contact with the wires for a moment if you have old spark plug wires with bad sealing boots and/or no dielectric grease on the spark plugs. You can pull your wire off the spark plugs, get a flashlight and see if any rust is developing on the spark plugs or inside the wire boots.
Do you have any warning lights comeing on when this happens?.