Seeing as I live in Seattle, I can talk about this pretty well:
The rain here is ALWAYS diagonal. There is no way to avoid it. It is even worse if you are in any area that is not sidewalk-ed, because you will get lovely trails of gravel and stuff up your legs. Rule number 1? NEVER WEAR LONG PANTS. I don't care how cold it is, long pants are a no-no because they will get destroyed. That being said, if you have to walk any distance, have a jacket that is waterproof. It's hard when you're on a VERY tight budget to find a fashionable waterproof jacket and I haven't found one yet. Your hood becomes your best friend here but it can get really windy so umbrellas are out most of the time. Also flip-flops are a must because if they get destroyed, they can be replaced cheaply, and you don't ruin them by walking in water.
Also if it was raining when I had to walk up to my school bus stop, I would do my makeup on the bus or on some days, not even bother. Also 2nd period Hollywood/History was a primo time to get my makeup done.
And hair? You're best off going simple, a ponytail or a bun with some gel.