If the water is below 70 degrees, I would definitely advise getting a wetsuit. The only decision then is, full or shorty and how thick.

Whatever you do, don't wear clothing that absorbs water--jeans, sweaters (cotton), tee-shirts. When wet, they become cold, heavy sponges.

In water temps in the high 50s with air temps in the low 60s (NC this time of year), you should be able to COMFORTABLY sail with a full wetsuit of 3mm thickness on the legs/arms and 4mm for the body.

Again, my opinion is that any water temps below 70 degrees deserve a wetsuit. Even with warm air temps...

Enjoy extending your sailing season!