A Technique for Anticipating Initial Rapid Increases in Intensity in Tropical Cyclones, Using 37 gHz Microwave Imagery

An alternative approach is proposed for aiding in forecasting significant rapid increases in intensity (>=25 kt / 24 hr) that commence when tropical cyclone intensity is initially in the 50-70 kt range: a focus on rainband structure in the core region of the tropical cyclone, preceding the development of deep convection, as observed in the higher-resolution 37 gHz microwave imagery. Specific features, visible as shallow convective rainbands, are shown to be present at the initiation of a period of rapid increase in intensity. During this period, successive microwave images reveal patterns identifying a continually-improving trend in structural organization. Conversely, tropical cyclones that lack these initial rainband patterns in the microwave imagery to begin with, or display the initial patterns, but fail to maintain a trend of improved organization, do not undergo rapid increases in intensity. Different trends are shown to each correlate with a specific range of intensity change. A forecast methodology is developed based on identification of these patterns in a comprehensive review of the 37 gHz microwave imagery of the 2003-2007 NATL hurricane seasons. This forecast methodology is evaluated, and correlated with the SHIPS RI Index for this set of named storms.