With a strong southwesterly crosswind the aircraft probably gave the "don't sink" warning in the Frankton Arm area shortly after getting airborne in an area of downflow on the leeside of the peninsula. Most operators when possible drift slightly north across to the Frankton Road side to then ride the updraught (cloud permitting) on the northern side of the arm after getting airborne, thereby getting out of the area of sink as soon as possible. Being a regular operator the pilot probably did this, and the "don't sink" would probably have been a brief transient while drifting across I would think. But having not been there at the time, we don't really know.