When liquid-solid adhesive forces are weaker than liquid cohesive forces, the liquid molecules are more attracted to each other than to the solid surface. This causes the liquid to minimize its contact with the solid. The surface curves outward, forming a convex meniscus. This is mathematically described by a positive contact angle θ > 90° in Young's equation: ${\gamma }_{sa}-{\gamma }_{sl}={\gamma }_{la}\cos \theta$, where weak adhesion results in a large θ.

Final answer: convex