Rapid Intensity Changes of Tropical Cyclones

Dear Colleagues,

Timely warning of tropical cyclone (TC) location and strength has the potential to save lives and reduce property damages. TC forecast models have been constantly improving in track predictions since the 1970s. In the North Atlantic Basin, while track errors by 48 hours were on the order of 250 nautical miles in the 1970s and 1980s, and about 150 nautical miles in the 1990s, further reduction of track errors to less than 100 nautical miles during the last decade has been possible due to improved numerical weather prediction models, observations to improve initialization of those models, and above all, advancements in our understanding of the environment in which the TC forms and evolves. The forecast improvement trend has been noticed in 5-day track predictions over the Atlantic and also over other global basins. For instance, the very severe cyclonic storm (VSCS) Phailin (2013) was the strongest cyclone to have hit the eastern coast of the India Odisha state since the super cyclone of 1999. However, there has never been a number of casualties as large as that of 1999, when approximately 10,000 fatalities were reported. Studies have correlated the reduction of loss of lives to improved warnings and better track predictions from numerical models.

Forecasting intensity changes in tropical cyclones is also an important forecast problem and becomes increasingly so especially in the case of storms that rapidly intensify or weaken just prior to landfall (e.g., TCs; Charley, 2004; Katrina and Wilma, 2005; Humberto, 2007; Karl, 2010, Phailin and Lehar, 2013; Michael, 2018; and Dorain, 2019). Evacuation becomes a challenge both when a tropical cyclone rapidly intensifies or if there is a false alarm of a rapidly weakening event. However, forecasting intensity changes in TCs is a complex and challenging multiscale problem. While cloud-resolving numerical models using a horizontal grid resolution of 1–3 km are starting to show results in predicting intensity changes in individual cases, improvements in predicting TC intensity changes have not kept pace with track predictions. Nevertheless, in order to address the intensity forecast problem, the National Oceanic and Atmospheric Administration (NOAA) created the Hurricane Forecast Improvement Program (HFIP) in 2009. The high-resolution Hurricane Weather Research and Forecasting (HWRF) system was created under this program. The HWRF system is showing some promise in removing the initial roadblocks associated with predicting intensity changes, dynamical prediction of which was nearly non-existent until 2009. Over the Atlantic basin, the model has shown about 20% improvements in intensity guidance. Similarly, the National Center for Atmospheric Research’s (NCAR’s) Weather Research and Forecasting (WRF) model has been used by the university community to gain some basic understanding on the TC intensification problem. Nevertheless, rapid intensification (RI), as measured by growth of the storm strength by 30 knots in 24 hours, as well as rapid dissipation of TCs, continues to be a great challenge to the forecasting community. For the most part, the lack of improvement in RI forecast ability is rooted in our lack of understanding of when and how RI occurs in different environmental conditions and the historic inability of dynamical models to accurately predict not only convection in the hurricane core, but also large-scale environmental factors such as shear and moisture that produce an RI event. We will dedicate this Special Volume of the journal Atmosphere to provide state-of-the-art and next generation efforts to advance our understanding of the TC rapid intensification and weakening problem.

Dr. Sundararaman Gopalakrishnan
Dr. Ghassan Alaka
Guest Editors

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• tropical cyclone (TC)
• tropical cyclone intensification
• rapid intensification (RI)
• rapid weakening in TC
• numerical weather prediction (NWP)
• tropical cyclone forecasting
• hurricane weather research and forecasting (HWRF)
• multiscale interactions in TCs
• cumulus convection
• vortical hot towers
• rain band
• inner-core TC structure
• shear