Understanding the Processes Causing the Early Intensification of Hurricane Dorian through an Ensemble of the Hurricane Analysis and Forecast System (HAFS)

Andrew Hazelton,Sundararaman Gopalakrishnan,Ghassan J Alaka,Michael Fischer,Levi Cowan

doi:10.3390/atmos12010093

Andrew Hazelton, Sundararaman Gopalakrishnan + Show 3 more

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The early stages of a tropical cyclone can be a challenge to forecast, as a storm consolidates and begins to grow based on the local and environmental conditions. A high-resolution ensemble of the Hurricane Analysis and Forecast System (HAFS) is used to study the early intensification of Hurricane Dorian, a catastrophic 2019 storm in which the early period proved challenging for forecasters. There was a clear connection in the ensemble between early storm track and intensity: stronger members moved more northeast initially, although this result did not have much impact on the long-term track. The ensemble results show several key factors determining the early evolution of Dorian. Large-scale divergence northeast of the tropical cyclone (TC) appeared to favor intensification, and this structure was present at model initialization. There was also greater moisture northeast of the TC for stronger members at initialization, favoring more intensification and downshear development of the circulation as these members evolved. This study highlights the complex interplay between synoptic and storm scale processes in the development and intensification of early-stage tropical cyclones.

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Understanding the processes underlying tropical cyclone intensity change continues to be a major goal of research in tropical meteorology
This bias was seen in several operational ensemble systems as well, including the GFS ensemble and even the European Center for Medium-Range Weather Forecasting (ECMWF) ensemble
The intensity forecasts showed a large range, with some members keeping the tropical cyclone (TC) as a weak tropical storm for several days, with others more correctly showing the intensification into a major hurricane

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Understanding the processes underlying tropical cyclone intensity change continues to be a major goal of research in tropical meteorology. Predicting tropical cyclone (TC) intensity change is important for many reasons, including providing accurate warnings of potential impacts. We examine the complexities associated with the early intensification of Hurricane Dorian (2019), one of the most devastating and powerful tropical cyclones of the 21st century [2]. The study explores key factors that allowed Dorian to intensify in the Eastern Caribbean despite the presence of marginal to hostile environmental conditions (including dry air), and the connection between the track and intensity of the TC during this critical early period. Davis and Bosart [3] studied numerical simulations of Hurricane Diana (1984), and found that its track was sensitive to the cumulus scheme chosen, because of how the associated precipitation and outflow affected the large-scale steering of the storm. Alaka et al [6]

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