Using remotely-sensed observations to describe tropical cyclone formation and evolution

The interpretation of a tropical cyclone's structure from satellite imagery has been a key element for structure and intensity estimation. One of the most important examples is the Dvorak technique, which was developed in the 1970s, and is still used in many tropical cyclone forecasting centers. This technique provides a source of tropical cyclone intensity estimates over the tropical oceans. The longevity of the Dvorak technique clearly speaks to the utility of satellite-based observations for tropical cyclone analysis. An aspect of tropical cyclone development that can clearly benefit from use of satellite-based observations is the genesis process. Tropical cyclones, for the most part, develop over oceans where traditional observation platforms such as rawinsonde stations cannot be located. Therefore, the best opportunity for locating and discriminating those cloud clusters that will develop into tropical cyclones from those that will not is from analysis of satellite-based observations.

This document introduces an objective technique, based on brightness temperature observations, which aims to discriminate those tropical cloud systems, which will develop into tropical cyclones from those that will not. The basis of the technique is that the convective structures embedded in cloud clusters become more axisymmetric as the wind field of the disturbance organizes and intensifies. To quantify this evolution, two tasks are required: 1) the center of the system needs to be located in an objective manner, and 2) the departure from axisymmetry of the weather system needs to be quantified. Time series of the combined results of these two tasks are used to examine the evolution of tropical disturbances.

In this presentation results from storms that developed in the Atlantic in 2005 will be shown. Time series of the departure from axisymmetry will be shown to be negatively correlated with the maximum sustained surface wind speed obtained from the National Hurricane Center best track archives. These results are encouraging as they appear to describe the evolution of tropical weather disturbances. In addition, it will be shown that the model has utility in identifying early stages of genesis as well as subsequent evolution of tropical cyclones.