Instead of waiting for Mother Nature to take her course, why not wait for a dry, sunny day to do some leak testing? Just use a garden hose with a spray nozzle. Not a stream, just a gentle spray, sort of like rain. Start low, near the cowl, and check for leaks. If it stays dry, move up the A pillar a bit. When you start seeing water, you've found the area that is leaking.
Do you have a roof rack? Don't neglect spraying around the mounting points. Water can seep through there, and flow to the A pillar.