Lighted object above Gulf of Mexico seen from St. Pete Beach displayed impossible up and down maneuvers and speed

Just after sunset on St. Pete Beach on August 18 we had gone out after a tremendous storm looking West into the Gulf of Mexico. There was lightning streaking across the sky.  On the beach we spotted a strange light hovering in the sky to the North. It suddenly shot straight down like an elevator then back up to a position about 30 degrees. The circular light began to move along the waterline at a height of about 3,000 feet. It then moved at a rapid rate of speed past us and to the South. I recorded this progress on my I Phone. I don't think it was a drone of any kind. There must have been hundreds of witnesses as this was a spectacular lightning display during and just after sunset.