Structural differences observed between weakening, steady state, and intensifying tropical cyclones

What is it about?

A missing link in our understanding of hurricane intensity change remains a thorough understanding of the mechanisms driving variability internal to the system. We examine a large set of hurricanes sampled by aircraft in the North Atlantic basin from 1999 to 2012 in an attempt to distinguish structural features in various composites, organized by intensity, intensification rate, age, and the presence of a secondary wind maximum. We note statistically significant differences when comparing composite-mean structures of wind, moisture, and vorticity (a local measure of rotation). Our principal findings demonstrate that weakening hurricanes differ in structure from intensifying hurricanes, which suggests that hurricane structure can be a useful aid in forecasting hurricane intensity.

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Why is it important?

In contrast to prior studies examining hurricane structural variability across a single dimension (e.g., intensity or intensity change), the large number of hurricanes sampled in the FLIGHT+ database provided an opportunity to simultaneously investigate hurricane structural variability across several dimensions. We demonstrated, among other things, that differences in the inner-core wind and vorticity structures between weakening, steady-state, and intensifying minor hurricanes (Category 1 and 2 on the Saffir-Simpson scale) are primarily manifested during the latter stages of the hurricane life cycle. On the other hand, differences in the outer-core wind and inner-core vorticity and moisture between major hurricanes (Category 3 and above on the Saffir-Simpson scale) are primarily manifested during the early stages of the hurricane life cycle. Therefore, one of our unique findings in this study demonstrated the significance of considering the "age" of a hurricane when assessing structural variability.

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