The trouble with Wanganui is as much related to river conditions as sea conditions. Following heavy rainfall there can be big standing waves at the entrance. Not a big deal leaving since you can pick your day but be wary entering the Wanganui Moles after heavy rainfalls. The positives are that after a big flood the seabed there gets smoothed out easing the waves encountered over the bar when you give it a few days.
I would make a crossing to Port Hardy on the NW side of Durville. It has a very big sheltered harbour. In WW2 the Japanese fleet sunk in the Battle of Coral Sea was reputed to be headed for Port Hardy after it had been scouted for suitability by a Japanese submarine.