Complex sentence: The second equation expresses that in the case the streamline has curvature there should exist the pressure gradient normal to the streamline because the centrifugal acceleration of the fluid parcel is only balanced by the normal pressure gradient.
Split into simpler sentences: The second equation expresses that the normal pressure gradient is balanced by the centrifugal acceleration of a fluid parcel. In the case the streamline has curvature, there should exist the pressure gradient normal to the streamline because the centrifugal acceleration of the fluid parcel is only balanced by the normal pressure gradient.