It is well known that the vertical shear of the wind exerts a strong control on tropical cyclone (TC) intensity change and genesis. However, since conventional measurements (i.e., rawinsondes and aircraft) of the atmospheric motion field are very sparse over the tropics, it is difficult to quantitatively assess the role of the shear. For instance, it is known from operational forecasting experience, that a TC can strengthen under "moderately" strong shear. However, a precise answer to the question "how much shear is too much?" has not yet been delivered by the research community.
For the last two hurricane seasons, UWisc/CIMSS has routinely produced high-resolution analyses of the vertical wind shear (150-300 mb layer mean minus 700-925 mb layer mean) from high-density satellite-derived cloud- and water vapor-tracked winds over the TPC/NHC area of forecast responsibility. In 1998, these fields are being made available to TPC/NHC in real time over the Internet. Because of the large amount of data that are input into these analyses, it is possible to make fairly reliable estimates of the strength of the shear over areas of interest. Several case studies from the 1997 and 1998 hurricane seasons are investigated. Preliminary findings suggest that these analyses may provide threshold values of vertical shear that are correlated with TC intensity change and (possibly) formation