POSTLANDFALL TROPICAL CYCLONE REINTENSIFICATION IN A WEAKLY BAROCLINIC ENVIRONMENT - A CASE-STUDY OF HURRICANE DAVID (SEPTEMBER 1979)

An analysis is conducted from a potential vorticity (PV) perspective o f 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 fi nal landfall in Georgia on 4 September 1979 and weakened rapidly there after. The noteworthy aspect of David was its subsequent reintensifica tion approximately 27 h after landfall as a warm-core disturbance in a weakly baroclinic environment. In this regard the redevelopment of Da vid is unlike the classical extratropical transformation of a tropical storm in a strongly baroclinic environment that has been documented i n the literature. The authors' analysis of the evolution of the dynami cal tropopause subsequent to storm landfall revealed that David reinte nsified in response to ''tropopause lifting'' (upward displacement of the dynamic tropopause) ahead of a nondeepening and otherwise very wea k upper-tropospheric disturbance. The ''tropopause lifting,'' associat ed with both advective and diabatic warming poleward and eastward of D avid, resulted in steepening of the tropopause and compaction of the P V maximum associated with the weak upper-tropospheric disturbance. As the compacted upper-level trough accelerated north-eastward, the assoc iated ascent and low-level horizontal convergence were rendered especi ally efficient in generating cyclonic vorticity by the neutral stabili ty (relative to the moist adiabat) of the moist tropical air mass surr ounding David and the presence of the preexisting low-level vorticity maximum associated with the remnant tropical storm circulation.