They do pretty damn good in the wet. By cold they mean below freezing, these are summer tires not meant for snow, the tires will harden up, which shouldn't be an issue since I doubt you'll be using the jetski in that weather.
It will do fine. Quit stressing about it. Front wheel drive is where people screw up on boat ramps. All of the weight from the load is transferred to the rear wheels when you are on a ramp. You will have more traction than on level ground due to the weight transfer to the rear. Your rear wheel drive Miata will be a win.
thanks allot guys, i gotta see if i can test it out some wer that theres no water so i cnt sink my car if sumtin bad does happen, maybe one of those loading ramps behind publix or sumtin.. lol thanks again