Climatic Variation of Maximum Intensification Rate for Major Tropical Cyclones over the Western North Pacific

Xiangbai Wu,Huan Mei,Yan Li,Gen Li,Xiao-Hai Yan,Yuei-An Liou

doi:10.3390/atmos12040494

Abstract

To analyze the dependence of intensification rates of tropical cyclones (TCs) on the variation of environmental conditions, an index is proposed here to measure the lifetime maximum intensification rates (LMIRs) for the Saffir–Simpson scale category 4–5 TCs over the western North Pacific. To quantitatively describe the intensification rate of major TCs, the LMIR is defined as the maximum acceleration in the sustained-wind-speed over a 24-h period of an overwater TC. This new index, LMIR, is generally independent of the indices for RI frequency. The results show that the Pacific Decadal Oscillation (PDO) modulates the inter-annual relationship between the LMIR and El Niño/Southern Oscillation (ENSO). The PDO’s modulation on the ENSO’s effect on the LMIR is explored here by considering the relationship between the LMIR and the environmental conditions in different PDO phases. While the ENSO’s effect on the LMIR for the warm PDO phase is generally by affecting the variations of upper ocean heat content, ENSO mainly influences the variations of zonal wind and vertical wind shear for the cold PDO phase. Our results suggest that fast translating TCs tend to attain strong intensification during the warm PDO phase, while a warm subsurface condition may permit slow-translating TCs also to become strongly intensified during the cooling PDO phase. These findings have an important implication for both prediction of RI and the long-term projection of TC activities in the western North Pacific.

Highlights

Three time series of the maximum sustained wind speed are shown in Figure 1a to demonstrate the physical meaning of lifetime maximum intensification rates (LMIRs)
Our results suggest that the variation of LMIR is closely related to El Niño/Southern Oscillation (ENSO), and their correlation reverses sign with a change in Pacific Decadal Oscillation (PDO) status
Our analysis shows that the LMIR is significantly correlated with the upper ocean heat

Summary

Introduction

RI is defined as an increase by at least 30 knots (15.4 m/s) over a 24-h period in the maximum sustained overwater wind speed [5]. Most major TCs (maximum sustained wind speed equal to or greater than 113 knots, categories 4 and 5 on the Saffir–Simpson hurricane wind scale), both in the Northern Atlantic and western North Pacific, experience at least one RI event during their lifetime [5,6]. The TC intensity change is difficult to forecast, as illustrated by unanticipated RI events, such as that which occurred during Hurricanes Opal (1995) and Bret (1999). The frequent underestimation of RI rates makes the TC intensity forecasting even more challenging, as detailed in a report on Hurricane Wilma [7] and with the record-breaking Hurricane Patricia [8]

Results

Discussion

Conclusion