Observational Analysis of Tropical Cyclone Formation. Part II: Comparison of Non-Developing versus Developing Systems

Abstract The thermodynamic and dynamic fields surrounding the composite tropical weather systems described in Part I (McBride, 1981a) are examined for differences between non-developing and developing systems. The main findings are as follows: (i) Both non-developing and developing systems are warm core in the upper levels. The temperature (and height) gradients are more pronounced in the developing system, but the magnitudes are so small that the differences would be difficult to measure for individual systems. (ii) The developing or pre-typhoon cloud cluster exists in a warmer atmosphere over a large horizontal scale, for example, out to 8° latitude radius in all directions. (iii) There is no obvious difference in vertical stability for moist convection between the systems. (iv) There is no obvious difference in moisture content or moisture gradient. (v) Pre-typhoon and pre-hurricane systems are located in large areas of high values of low-level relative vorticity. The low-level vorticity in the vicinit...