Hurricane Isabel (2003): new insights into the physics of intense storms Pt.1 mean vortex structure and maximum intensity estimates

Abstract

This study is an observational analysis of the inner-core structure, sea surface temperature, outflow layer, and atmospheric boundary layer of an intense tropical cyclone whose intensity and structure is consistent with recent numerical and theoretical predictions of superintense storms. the finding suggest new scientific challenges for the current understanding of hurricanes.. Unprecedented observations of category 5 Hurricane Isabel (2003) were collected during 12-14 September. This two-part series reports novel dynamic and thermodynamics aspects of the inner-core structure of Isabel on 13 September made possible by analysis of these data. Here, a composite of the axisymmetric structure of the inner-core and environment of Isabel is estimated using Geostationary Positioning System dropwindsondes and in-situ aircraft data. In Part II, an extreme wind speed observation on the same day is discussed in the context of this work. The axisymmetric data composite suggest a reservoir of high entropy air inside the low-level eye and significant penetration of inflowing near-surface air from outside. the analysis suggests that the low-level air penetrating the eye is enhanced thermodynamically by acquiring additional entropy through interaction with the ocean and replaces air mixed out of the eye. The results support the hypothesis that this high entropy eye air "turbo-boosts" the hurricane engine upon its ejection into the eyewall clouds. Recent estimates of the ratio of sea-to-air enthalpy and momentum exchange at high wind speed are used to suggest that Isabel utilized this extra power to exceed the previously assumed intensity upper bound by 10 to 35 m s(-1) for the given environmental conditions. Additional study with other data sets is encouraged to further test the superinstensity hypothesis.