The other feature near Central America has been producing a broad area of thunderstorms and will be interacting with the monsoon trough that remains in that area. The Tropical Analysis Branch is calling the area a "Very Dangerous Situation" as continuous and heavy rain will likely drench parts of Central America.
It was this type of setup that helped Arlene deepen into a cyclone 2 weeks ago. All of the forecast models lower surface pressures in that area and show very low wind shear, but most favor the Pacific side for cyclone development. It is possible however that development occurs on both sides of Central America. The main hindrance on the Caribbean side is the proximity to land.