Relationship between Early-Stage Features and Lifetime Maximum Intensity of Tropical Cyclones over the Western North Pacific

Ren Lu,Xiaodong Tang

doi:10.3390/atmos12070815

Abstract

The relationship between early-stage features and lifetime maximum intensity (LMI) of tropical cyclones (TCs) over the Western North Pacific (WNP) was investigated by ensemble machine learning methods and composite analysis in this study. By selecting key features of TCs’ vortex attributes and environmental conditions, a two-step AdaBoost model demonstrated accuracy of about 75% in distinguishing weak and strong TCs at genesis and a coefficient of determination (R2) of 0.30 for LMI estimation from the early stage of strong TCs, suggesting an underlying relationship between LMI and early-stage features. The composite analysis reveals that TCs with higher LMI are characterized by lower latitude embedded in a continuous band of high low-troposphere vorticity, more compact circulation at both the upper and lower levels of the troposphere, stronger circulation at the mid-troposphere, a higher outflow layer with stronger convection, a more symmetrical structure of high-level moisture distribution, a slower translation speed, and a greater intensification rate around genesis. Specifically, TCs with greater “tightness” at genesis may have a better chance of strengthening to major TCs (LMI ≥ 96 kt), since it represents a combination of the inner and outer-core wind structure related to TCs’ rapid intensification and eyewall replacement cycle.

Highlights

Tropical cyclones (TCs), one of the most catastrophic weather events over the WesternNorth Pacific (WNP), have caused huge damage with strong winds and heavy precipitation for decades [1,2]
In step 1, we use accuracy and F1-score as the metrics to evaluate the fitting capability of classifier: 1 =
It is clear in the table that whether accuracy or F1-score is chosen as the criterion, the classifier based on AdaBoost ensemble is ranked first

Summary

Introduction

Tropical cyclones (TCs), one of the most catastrophic weather events over the WesternNorth Pacific (WNP), have caused huge damage with strong winds and heavy precipitation for decades [1,2]. Gray [16,17] noted several favorable factors for TC genesis, including thermodynamic factors of sufficient ocean thermal energy, conditional instability throughout the low troposphere and high relative humidity in the mid-troposphere, and dynamic factors of a large enough Coriolis parameter, above-normal low-level vorticity, and weak vertical wind shear near the center of a TC’s circulation. He further emphasized the key roles of climate conditions (e.g., region, season, etc.), certain synoptic flow patterns (e.g., monsoon trough), and active mesoscale convective systems (MCSs) in TC genesis. The genesis potential index (GPI) [18,19] was developed to quantitively assess the probability of TC genesis at a certain location, which suggests some key factors for LMI as well

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Conclusion