On August 31, a large tropical wave moved off the west coast of Africa. A tropical system along the wave axis contained a low pressure area as well as an impressive outflow pattern, though originally its convection was disorganized and limited. By September 1 a cyclonic circulation with a diameter of 690 mile (1115 km) was seen on satellite imagery, well to the southeast of the Cape Verde Islands, and several hurricane forecast models expected development and strengthening. As it moved quickly westward, the convection organized and developed into rainbands–bands of showers and thunderstorms that move in a spiral direction towards the center of the storm–and late on September 1 meteorologists began tracking the system using the Dvorak technique. Low amounts of wind shear and favorable outflow allowed strong deep convection to develop and persist near the center, and by 1800 UTC on September 2 the system developed into Tropical Depression Nine about 450 miles (730 km) southwest of Praia, Cape Verde.