Trends in Western North Pacific Tropical Cyclone Intensity Change Before Landfall

Qingyuan Liu,Philip J Klotzbach,Jinjie Song

doi:10.3389/feart.2021.780353

Abstract

This study investigates the long-term trend in the average 24-h intensity change (ΔV24) of western North Pacific (WNP) tropical cyclones (TCs) before landfall during June-November for the period from 1970–2019. We find a significant increasing trend in basin-averaged ΔV24 during 1970–2019. The increase in ΔV24 is significant over the northern South China Sea (17.5°-25°N, 107.5°-120°E) and to the east of the Philippines (7.5°-15°N, 122.5°-132.5°E), implying a slower weakening rate before landfall for the South China Sea and an increased intensification rate before landfall for the region east of the Philippines. We find a significant linkage between changes in ΔV24 and several large-scale environmental conditions. The increased ΔV24 before landfall in the above two regions is induced by a warmer ocean (e.g., higher sea surface temperatures, maximum potential intensity and TC heat potential) and greater upper-level divergence, with a moister mid-level atmosphere also aiding the ΔV24 increase east of the Philippines. Our study highlights an increasing tendency of ΔV24 before landfall, consistent with trends in ΔV24 over water and over land as found in previous publications.

Highlights

Tropical cyclones (TCs) are one of the most devastating global natural disasters, inducing large economic losses as well as fatalities for various coastal regions
TC intensity change is the result of a complex interaction between various internal influences that are related to the structure and internal processes of the TC itself and various external influences that are controlled by the largescale atmospheric and oceanic environment (Hendricks et al, 2019)
There are no significant changes in 850-hPa relative vorticity and 850–200hPa vertical wind shear (VWS) over Regions A and B (Figures 4F,H), indicating that changes in these variables related to the low-level environmental circulation have only had minor impacts on TC intensity changes before landfall

Summary

INTRODUCTION

Tropical cyclones (TCs) are one of the most devastating global natural disasters, inducing large economic losses as well as fatalities for various coastal regions. There are no significant changes in 850-hPa relative vorticity and 850–200hPa VWS over Regions A and B (Figures 4F,H), indicating that changes in these variables related to the low-level environmental circulation have only had minor impacts on TC intensity changes before landfall. SST, MPI, TCHP and 200-hPa divergence significantly increase to the south of Japan (27.5°-35°N, 127.5°-135°E), there are no significant changes in the average ΔV24 before landfall. The lack of trend may be related to the low number of TCs occurring over this region (1.2 TCs per year on average) This low TC frequency can lead to large variability in the annual change of average ΔV24, subsequently reducing the significance of the long-term trend

SUMMARY

Findings

DATA AVAILABILITY STATEMENT