Eastern Pacific Hurricanes Jimena of 1991 and Olivia of 1994: The Effect of Vertical Shear on Structure and Intensity

Abstract Shear is a key inhibitor of tropical cyclone intensification. Although its signature is readily recognized in satellite imagery and theoretical or modeling studies provide some insight, detailed observations have been limited. Airborne radar and in situ observations in Hurricanes Jimena of 1991 and Olivia of 1994 are a step toward better understanding. Each storm was observed on two consecutive days. Initially, both had small eyes, 16–18-km radius, and maximum winds of ∼57 m s−1 over sea surface temperatures (SST) >28°C in easterly environmental shear. Jimena maintained constant intensity or weakened gradually for 2 days in 13–20 m s−1 easterly shear. Olivia intensified in 8 m s−1 shear on the first day. Overnight, the shear diminished to reverse and became westerly. On the second day, Olivia weakened as the shear increased to >15 m s−1 from the west, the storm moved over cooler SST, and became surrounded by dryer air. As convection weakened and the outer rainbands ceased to be effective barriers...

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