Singing In The Rain
If you are determined to be out in it I would recommend that you put a cover over your camera and lens. Promaster, Aquatec, and Think Tank make sturdy custom covers for even long lenses and large cameras - if you just need an emergency wrap try the Op/tec ones. You get two in a bag and they can save a lifetime of trouble with a wet camera.
Remember as well, that if they keep water out, they can also keep it in. Once you are safely housed please remove the camera and make sure the inside of the cover gets a chance to air out.