A right-moving storm, often shortened to right mover, is a thunderstorm whose motion deviates to the right of the mean wind, typically the cyclonic member of a splitting storm and the one most likely to organize into a supercell in Northern Hemisphere shear environments. The rightward deviation is driven by internal storm dynamics rather than a change in the environmental wind.
Why it deviates right
A rotating updraft in a sheared environment produces its own dynamic pressure field. On the cyclonic flank of the storm, a mid-level dynamic low forms that draws additional upward motion into that side. The storm effectively grows preferentially into that pressure minimum, and its center of mass drifts to the right of the mean flow.
This rightward push comes from internal storm dynamics rather than from any change in the environmental wind. The mean wind is still steering the storm at first order; the deviation is what the rotating updraft adds on top.
How forecasters anticipate it
The Bunkers method is the standard approach. On a hodograph, forecasters draw the mean wind through roughly the lowest six kilometers and the shear vector across the same layer, then plot two predicted supercell motions offset about seven to eight meters per second to either side of the mean wind along the line perpendicular to the shear vector. The right-mover vector sits on the clockwise side of the shear vector; the left-mover sits on the other side.
Storm-relative helicity and other shear parameters are then computed using the right-mover motion, because that is the motion a rotating supercell is most likely to take. Forecasters who skip this step will typically underestimate the low-level rotation available to the storm.
Important limits
Individual right-moving storms often move faster or slower than the Bunkers vector predicts, sometimes by a large margin. Highly deviant tornadic supercells have been documented moving well to the right of the forecast motion, especially near boundaries or during tornado occurrence itself.
The Bunkers vector is a first guess, not a promise. It also does not decide whether the storm will actually rotate; it only says where a rotating storm is likely to go if one forms.