extrude? on a curved surface??

ok so i am trying to make this part with the ribs. the picture on the right shows what i need to draw looking at the top STRAIGHT on. BUT the entire rib needs to be PERPENDICULAR to the curved surface... i have also attached a picture of how it looks based on how its drawn. i have no idea how to make the ribs constant to the curved surface throughout the curved rib. anything else needed just ask. thanks in advance.

SolidworksParts And Features