usually air and weather temps are OK by May if you have a decent wetsuite. If you're well equipped with booties and hood you can hit the water by late March-April (but it's chilly).
offers now lessons and clinics in New Jersey as well as NY, CT, RI and Cape Cod. I recommend you take advantage of spring season by taking the "dry lessons" they offer. You'll be amazed by how much ground you can cover by familiarizing with flying stunt kites, smaller traction kites and body dragging on the beach. Also learning about equipment and a complete understanding of how to keep kitesurfing safe for you and others will help you get in the water with much confidence ! From there the learning curve will be incredible fast.
I believe there will be dates available for classes both in Sandy Hook as well as Lakes Bay in the southern Jersey shores.
Enjoy and be safe !