Tropical cyclone fullness: A new concept for interpreting storm intensity

Intensity and size are two crucial factors in determining the destructiveness of a tropical cyclone (TC), but little is known about the relationship between them because of a lack of observations. TC fullness, a new concept, is proposed to quantitatively measure the storm wind structure, which is defined as the ratio of the extent of the outer-core wind skirt to the outer-core size of the TC. TC intensity is more strongly correlated with fullness than with other measures comprising just a single size parameter. A scale is introduced to classify TCs into four categories based on TC fullness (FS1 to FS4). Regardless of the specific inner-core and outer-core size, the FS4 fullness structure is necessary for an intense TC's development, while category FS1 and FS2 TCs are generally weak. Most major TCs achieve FS4 fullness structure earlier and more frequently than nonmajor TCs. Rapidly increasing fullness favors the intensification of TC. Plain Language Summary Tropical cyclone (TC) disasters caused tremendous property loss and casualties all over the world every year, while the knowledge on what essentially determines TC intensity is far beyond enough. Should a large TC ought to be intense and disastrous? And is a small TC doomed to be weak? It confused us when some dapper small TCs struck us with their fierce wind and torrential rain, while other large TCs that finally turned out to be a false alarm tricked us with their puffiness body. The underlying factor that truly controls TC intensity has been grasped here. We unveil the mysteries between TC intensity and size by raising a new concept: TC fullness. Either small or large TC can be intense; it depends on the fullness. TCs should possess FS4 fullness structure (high fullness) as long as they are intense; on the other hand, TCs with low fullness are weak in majority. In addition, rapidly increasing fullness is beneficial for the intensification of TC. The concept of TC fullness may provide a new path in the exploration of TC intensity and intensity change and may also be helpful for the forecast of TC intensity even its future change.