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Postlandfall Tropical Cyclone Reintensification in a Weakly Baroclinic Environment: A Case Study of Hurricane David (September 1979)

Lance F. BosartDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

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Gary M. LackmannDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

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Abstract

An analysis is conducted from a potential vorticity (PV) perspective of the reintensification of Tropical Storm David over the northeastern United States in September 1979. David, a major long-lived hurricane, originated near the Cape Verde Islands in late August 1979. It made final landfall in Georgia on 4 September 1979 and weakened rapidly thereafter. The noteworthy aspect of David was its subsequent reintensification approximately 27 h after landfall as a warm-core disturbance in a weakly baroclinic environment. In this regard the redevelopment of David is unlike the classical extratropical transformation of a tropical storm in a strongly baroclinic environment that has been documented in the literature. The authors' analysis of the evolution of the dynamical tropopause subsequent to storm landfall revealed that David reintensified in response to “tropopause lifting” (upward displacement of the dynamic tropopause) ahead of a nondeepening and otherwise very weak upper-tropospheric disturbance. The “tropospheric lifting,” associated with both advective and diabatic warming poleward and eastward of David, resulted in steepening of the tropopause and compaction of the PV maximum associated with the weak upper-tropospheric disturbance. As the compacted upper-level trough accelerated north-eastward, the associated ascent and low-level horizontal convergence were rendered especially efficient in generating cyclonic vorticity by the neutral stability (relative to the moist adiabat) of the moist tropical air mass surrounding David and the presence of the preexisting low-level vorticity maximum associated with the remnant tropical storm circulation.

Abstract

An analysis is conducted from a potential vorticity (PV) perspective of the reintensification of Tropical Storm David over the northeastern United States in September 1979. David, a major long-lived hurricane, originated near the Cape Verde Islands in late August 1979. It made final landfall in Georgia on 4 September 1979 and weakened rapidly thereafter. The noteworthy aspect of David was its subsequent reintensification approximately 27 h after landfall as a warm-core disturbance in a weakly baroclinic environment. In this regard the redevelopment of David is unlike the classical extratropical transformation of a tropical storm in a strongly baroclinic environment that has been documented in the literature. The authors' analysis of the evolution of the dynamical tropopause subsequent to storm landfall revealed that David reintensified in response to “tropopause lifting” (upward displacement of the dynamic tropopause) ahead of a nondeepening and otherwise very weak upper-tropospheric disturbance. The “tropospheric lifting,” associated with both advective and diabatic warming poleward and eastward of David, resulted in steepening of the tropopause and compaction of the PV maximum associated with the weak upper-tropospheric disturbance. As the compacted upper-level trough accelerated north-eastward, the associated ascent and low-level horizontal convergence were rendered especially efficient in generating cyclonic vorticity by the neutral stability (relative to the moist adiabat) of the moist tropical air mass surrounding David and the presence of the preexisting low-level vorticity maximum associated with the remnant tropical storm circulation.

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