Some of this was discussed on the last few pages of this thread:
Why Do Cobra Owners Sell So Fast?
Here are my thoughts:
I have found that in a standard rain storm with normal size drops, rain will blow right over the top of the cobra if you are moving faster than about 40mph.
HOWEVER, some exceptions:
- Deluge-style thunderstorms with huge drops don't all blow over
- Water will land on the back of the car and roll back down into the cockpit. Doesn't get you wet, but gets carpet wet
- Lay the visor horizontal or rain hits it and drops on the dash
- Water will come up from the front wheels and in around the door seals (which aren't great, at least on my car - if it was a regular occurrence, I'd probably play with better weather stripping)
- Some water will come around the windshield and drip onto your leg
- You better hope there aren't any lights or stop signs....
- The look on people's faces when you go by in a rainstorm in a cobra with no top is priceless.
I also carry a car cover and a tonneau (not one you can drive with) if I'll be out and might want to cover the car during a rain storm. Someone else suggested carrying a large golf umbrella as another option.