Pouring rain = high humidity, right? if you've got a marginal connection somewhere, it's possible that just a wet, muggy day will provide enough conductivity to make things work right. Check every connection- - - -which means disconnect it, wire brush it clean, and reconnect firmly. Pay particular attention to grounds- - - -the mounting of the alternator to the engine, ground straps or cables between the body and frame, and the battery cable connections on both posts. One of my students many years ago brought his mother's car into the school shop. It was a Buick Electra 225 with a 455 engine that had a slow cranking problem on a hot start. It had already had two batteries, a starter, and three alternators changed without solving the problem. We did a series voltage drop test on the starting system and found a loose, dirty connection where the battery ground cable attached to the engine block. 10 minutes with a wire brush, plus a new bolt and lock washer fixed the problem for good. That one connection was dropping nearly 2 volts during cranking, leaving less than 10 volts to run the starter.
Jerry
