Large Intensity Changes in Tropical Cyclones: A Case Study of Supertyphoon Flo during TCM-90

Abstract

Abstract A unique dataset, recorded during the rapid intensification and rapid decay of Typhoon Flo, is analyzed to isolate associated environmental conditions and key physical processes. This case occurred during the Tropical Cyclone Motion (TCM-90) field experiment with enhanced observations, especially in the upper troposphere beyond about 300 km. These data have been analyzed with a four-dimensional data assimilation technique and a multiquadric interpolation technique. While both the ocean thermal structure and vertical wind shear are favorable, they do not explain the rapid intensification or the rapid decay. A preconditioning phase is defined in which several interrelated factors combine to create favorable conditions: (i) a cyclonic wind burst occurs at 200 mb, (ii) vertical wind shear between 300 and 150 mb decreases 35%, (iii) the warm core is displaced upward, and (iv) 200-mb outflow becomes larger in the 400–1200-km radial band, while a layer of inflow develops below this outflow. These condit...