Low amounts of wind shear and favorable outflow allowed vigorous 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 .
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 .