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If the auto-spark hasn;'t already done so it may be prudent to get the battery load tested and the alternator output checked - if only to rule out that possibility.
After rain have you checked the insides of the fuse boxes for water ingress. It also may be worth checking out the windscreen scuttle panel drains ain't blocked. It's possible that only during heavy rain they can't cope.
Currently in madnoel10's garage:
Honda Civic 1.4l