The leading sunspot (whirl on the right) has a whirl-velocity on its equator-side in the same direction as the differential rotation (longest arrow with 2 000 m/s). Therefore the resulting velocity is high here and the pressure is low (low pressure area) - due to the Bernoulli-effect. In direction of the poles, the whirl rotates against the differential rotation (shorter arrow with 1 700 m/s). This causes a low velocity and a high pressure. The pressure relations around the leading whirl cause its drifting towards the equator (small black arrow in the whirl). These relations are reversed in the attached following sunspot i.e. whirl, therefore it drifts polewards.
The book: "The Electric Universe" by Dr. László Körtvélyessy