Using the gridded atmospheric
motion vector output u and v AMV components are averaged
over an upper layer (150, 200, 250, and 300 hPa) and a lower
layer (700, 775, 850, and 925 hPa). The difference in these
averaged components is used to compute the speed shear between
the upper and lower layers. The contours show the vector
magnitude shear (absolute value). The streamlines indicate the
direction of the shear.
In the case when a tropical cyclone (TC) is present, the analyses
are modified in the storm region by a procedure which removes
the storm circulation within a prescribed radii. This allows a more
representative depiction of the environmental shear acting on
The presence/lack of atmospheric wind shear is vital to
hindering/supporting TC development.
A low shear environment is favorable for tropical cyclone development,
while a high shear environment will deter a immature TC region from
(further) developing or destroy an already mature TC.
Shear values below 10 m/s (20 kts) are considered low enough for
For more AMV information, please visit the
International Winds Working Group (IWWG)