The wind moments are wind forces times the distance from the center of pressure to the point that the moments are summed around. In this case the moments are summed around the intersection of the tank shell and the bottom. The horizontal force is the horizontal wind pressure times the tank vertical projected area (height times diameter). The moment arm is half the tank Height. The wind pressure is determined in 3.2.1f. The vertical force is the wind pressure times the horizontal projected area (diameter squared * Pi / 4) and the moment arem is half the tank diameter. The vertical pressure is also determined in 3.2.1f. Add to this any moment due to internal pressure. The total resulting moment is resisted by moments resulting from the tank dead weight and/or liquid, per 3.11.2 for unanchored tanks and 3.11.3 for anchored tanks. Hope this helps...