Fujiwhara effect
Hurricane Diane originated in a tropical wave first observed as a tropical depression on August 7 between the Lesser Antilles and Cape Verde. The system moved generally to the west-northwest, intensifying into a tropical storm on August 9. By the time the Weather Bureau first classified the storm on August 10, Diane was south of the Bermuda high, a semi-permanent ridge in the jet stream just east of Nova Scotia. Ships in the region of the storm reported winds of . During the next day, the Hurricane Hunters reported no increase in strength, and Diane initially remained disorganized. The storm interacted with Hurricane Connie to its northwest in a process known as the Fujiwhara effect, in which Diane turned toward the north. Quick intensification ensued, potentially due to interaction with a cold-core low that increased atmospheric instability. On August 12, the storm rapidly intensified into a hurricane. The intensification was so quick that a ship southeast of the center believed Diane was undergoing a loop due to a steady drop in barometric pressure, despite moving away from the hurricane.