The Relative Importance of Factors Influencing Tropical Cyclone Rapid Intensity Changes

• Published in: Geophysical research letters 2019-02, Vol.46 (4), p.2282-2292
• Main Authors: Bhalachandran, Saiprasanth, Haddad, Ziad S., Hristova‐Veleva, Svetla M., Marks Jr, F. D.
• Format: Article
• Language: English
• Subjects: Aerodynamics; Amplification; Amplitudes; bay of bengal; Computer simulation; Cyclones; Data assimilation; Data collection; Empirical analysis; Evolution; Frameworks; Hurricanes; Identification; Initial conditions; linear discriminant analysis; Mathematical models; Modelling; Moisture flux; Nonlinear systems; Nonlinearity; Precipitation; rapid intensification; rapid weakening; symmetric and asymmetric convection; Tropical climate; Tropical cyclone; Tropical cyclone intensities; Tropical cyclones; Vertical wind shear; Vortices; Wave number; Wavelengths; Wind shear; Winds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL079997

Predicting rapid intensity changes in tropical cyclones (TCs) is a major challenge due to the influence of multiple competing processes within the vortex and in the TC environment. We present an empirical framework that quantifies the relative importance of the various factors that influence critical transitions in TC intensities. Our analysis of model simulations of recent TCs over the Bay of Bengal identifies the following variables within the vortex as the biggest influence on TC rapid intensity changes: the amplitudes of wave number 1 of 700‐ to 850‐mb horizontal moisture flux convergence and precipitation in the rainband region and the amplitude of wave number 0 of precipitation within the radius of maximum winds. Likewise, the most important environmental variables identified are the angle between the driest air and the shear vector and the magnitude of vertical wind shear. These findings provide guidance on guidance for future observational efforts and data assimilation into TC forecasting models. Plain Language Summary Critical transitions in tropical cyclone (TC) intensities are often very hard to predict because an intensity change is driven by multiple competing processes that act simultaneously in a complex and nonlinear fashion. To accurately forecast a TC's intensity evolution, it is very important to provide the best possible initial states to the forecast model. However, in reality, there are uncertainties in our knowledge of the initial state. This, coupled with the inherent nonlinearity in the system, makes it unwise to rely solely on deterministic forecasts. With this in mind, we derive empirical estimates of rapid intensification and weakening based on the current state of variables in the environment and in the vortex. Our framework identifies a set of important variables that are significantly different during time periods that just precede a rapid intensification as opposed to a rapid weakening. Our methodology then ranks the variables identified based on how their associated variability will be magnified over the course of model forecasts and how significantly they influence a rapid intensity change in a TC. The highest ranked variables must be prioritized in future observational and consequent modeling efforts that incorporate such observations as initial conditions of TC forecast models. Key Points A framework that computes the relative importance of the competing processes driving tropical cyclone rapid intensity changes is prese