The pilot stated he departed from the North Perry Airport and proceeded toward the Opa Locka Airport to pick up his first banner of the day. He noted thunderstorms in the area but their banner operations were still ongoing. Two of his coworkers picked up their banner before him. He deployed the hook and flew the pattern for the pick up. Upon approaching the poles, he applied full engine power and picked up the rope. He pulled up and upon the ground crew signaling that the banner is about to be lifted, he proceeded to lower the nose of the airplane, which was about 175 feet above the ground. At that point, instead of the usual leveling off, the airplane started to sink and upon picking up the banner, the sink rate accelerated rapidly. He waited about 2 seconds for things to normalize while ensuring all engine levers were in the full power position. The sink rate kept the same. By now he was sure that a hard landing was imminent so he released the banner and landed straight ahead.