 A tropical wave moved off the coast of Africa on September 10 , with evidence of a low @-@ level circulation and convective banding . It moved west @-@ northwestward , located south of a subtropical ridge . Based on satellite imagery , it is estimated the system organized into Tropical Depression Nine by 1200 UTC on September 11 to the south of the Cape Verde islands . Upon its formation , the center was poorly defined , with restricted easterly outflow due to easterly wind shear . After about 24 hours of remaining somewhat disorganized , the convection became more concentrated on September 12 as banding features and outflow improved . Consequently , the National Hurricane Center ( NHC ) upgraded the depression to Tropical Storm Gert , the seventh named storm of the season . 
