FIG. 29. Magnitude of the AugustOctober 1999 mean and anomalous vertical wind
shear. Wind shear is calculated as the difference in wind speeds between 200-hPa and
850-hPa (contour interval is 4 m s-1). Shaded areas in (a) indicate where the
vertical wind shear is less than 8 m s-1, and are considered favorable for
tropical cyclone formation. Below-average wind shear values in panel (b) are shaded red,
while above-average shear values are shaded blue.