Ensemble random forest for tropical cyclone tracking

Abstract

Even though tropical cyclones (TCs) are well documented during the intense part of their lifecycle until they weaken, many physical and statistical properties governing them are not well captured by gridded reanalysis or simulated by Earth System Models. Thus, tracking TCs remains a matter of interest for investigating observed and simulated tropical cyclones. Two types of cyclone tracking schemes are available. On the one hand, some trackers rely on physical and dynamical properties of the TCs and user-prescribed thresholds, which make them rigid. They need numerous variables that are not always available in the models. On the other hand, trackers leaning on deep learning need, by nature, large amounts of data and computing power. Besides, given the number of physical variables required for the tracking, they can be prone to overfitting, which hinders their transferability to climate models. This study explores the ability of a Random Forest (RF) approach to track TCs with a limited number of aggregated variables. Our analysis focuses on the Eastern North Pacific and North Atlantic basins, for which 514 and 431 observed tropical cyclone track records are available from the IBTrACS database during the 1980–2021 period. For each 6-hourly time step, RF associates TC occurrence or absence (1 or 0) to atmospheric situations described by predictors extracted from the ERA5 reanalysis. Hence, the tracking is considered a binary supervised classification problem of TC-free (zero) and TC (one) situations. Then, situations with TC occurrences are stitched to reconstruct TC trajectories. Results show the good ability and performance of this method for tracking tropical cyclones over both basins and good temporal and spatial generalisation. RF has a similar TC detection rate as trackers based on TCs’ properties and a significantly lower false alarm rate. RF allows us to detect TC situations for diverse predictor combinations, which brings more flexibility than threshold-based trackers. Last but not least, this study sheds light on the most relevant variables for tropical cyclone detection.