4 , ▁the ▁N HC ▁began ▁monitoring ▁a ▁tropical ▁wave ▁and ▁its ▁associated ▁con ve ction ▁off ▁the ▁west ▁coast ▁of ▁Africa ▁for ▁potential ▁development . ▁Ste ered ▁north west ▁toward ▁a ▁weak ness ▁in ▁the ▁subt rop ical ▁r idge ▁over ▁the ▁central ▁Atlantic , ▁the ▁wave ▁organized ▁sufficiently ▁to ▁become ▁a ▁tropical ▁de pression ▁by ▁ 1 8 : 0 0   UTC ▁on ▁August   1 6 . ▁The ▁de pression ▁slowly ▁organized ▁after ▁formation ▁and ▁developed ▁of ▁a ▁central ▁dense ▁over cast ▁feature , ▁with ▁the ▁system ▁becoming ▁Trop ical ▁Storm ▁F iona ▁by ▁ 1 2 : 0 0   UTC ▁on ▁August   1 7 . ▁Despite ▁strong ▁w ester ly ▁she ar , ▁abund ant ▁mid - level ▁dry ▁air , ▁and ▁an ▁otherwise ▁dis he ve led ▁satellite ▁appearance , ▁an ▁advanced ▁scatter ometer ▁( AS CAT ) ▁pass ▁indicated ▁a ▁maximum ▁sust ained ▁wind ▁speed ▁of ▁ 5 0   m ph ▁( 8 5   km / h ) ▁early ▁on ▁August   1 9 . ▁Although ▁sp or adic ▁burst s ▁of ▁con ve ction ▁continued ▁amid ▁the ▁host ile ▁environment , ▁F iona ▁weak ened ▁to ▁a ▁tropical ▁de pression ▁by ▁ 0 6 : 0 0   UTC ▁on ▁August   2 2 ▁and ▁deg ener ated ▁into ▁a ▁rem nant ▁low ▁early ▁on ▁August   2 3 ▁about ▁ 3 7 5   mi ▁( 6 0 5   km ) ▁south - s outh west ▁of ▁B erm