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