A strong tropical wave moved off the coast of Africa late on August 20, and almost convective banding and a broad circulation. A large area of low pressure formed within the wave the next day while located 260 miles southeast of the Cape Verde islands. Though convection decreased early on August 21, the area of low pressure stayed well-organized and the system developed into Tropical Depression Four late on August 21. Water temperatures remained warm enough for development, while upper level shear was minimal as the depression moved west-northwestward because of a ridge of high pressure to its north. Original predictions by the National Hurricane Center also forecasted a turn to the northwest based computer model predictions, as quoted by forecaster James Franklin, "The models have also been excellently wrong thus far".