1995 Volkswagen Jetta starting problem

Hi I have a problem starting the car first thing in the morning when it's raining. It just cranks and cranks and tries to start, sputters, and after 5 or 10 minutes of doing that, its starts. Then after that for the rest of the day, it will start right up. It doesn't happen on sunny days, only rainy days. I've tried spraying wd40 on cap, wires and coil, but it doesn't help. I'm suspecting it's the coil because the wires, plugs and cap were replace about 1-1/2 yrs. Ago. The problem seems to be getting worse. Any advice? Thanks.