OK, thanks for the info, quite helpful. I've already got the metvuw site bookmarked.
Unfortunately it doesn't provide accurate forecasts 18 months in advance
so as a general principle, subject to change as I get near the coast and pick up forecasts, what do you think of the plan of heading direct to Nelson across Tasman Bay, clearing in there, hanging out for a decent weather window, and then heading up past d'Urville island and into the strait from there. Stopping perhaps to duck into the Marlborough Sounds if it looks a bit hairy? Time of year would be mid January.
Is it worth ducking into Q. Charlotte Sound anyway and going out via Okukari? Or best head around the top so I don't have to play tag with ferries? Similarly French Pass inside the big island looks like it might save some miles at the expense of potential current issues, what would the local advice be?