A Statistical Analysis of the Effects of Vertical Wind Shear on Tropical Cyclone Intensity Change over the Western North Pacific

Abstract

The effect of vertical wind shear (VWS) between different pressure levels on TC intensity change is statistically analyzed based on the best track data of tropical cyclones (TCs) in the western North Pacific (WNP) from the Joint Typhoon Warning Center (JTWC) and the ECMWF interim reanalysis (ERA-Interim) data during 1981–2013. Results show that the commonly used VWS measure between 200 and 850 hPa is less representative of the attenuating deep-layer shear effect than that between 300 and 1000 hPa. Moreover, the authors find that the low-level shear between 850 (or 700) and 1000 hPa is more negatively correlated with TC intensity change than any deep-layer shear during the active typhoon season, whereas deep-layer shear turns out to be more influential than low-level shear during the remaining less active seasons. Further analysis covering all seasons exhibits that a TC has a better chance to intensify than to decay when the deep-layer shear is lower than 7–9 m s−1 and the low-level shear is below 2.5 m s−1. The probability for TCs to intensify and undergo rapid intensification (RI) increases with decreasing VWS and increasing sea surface temperature (SST). TCs moving at slow translational speeds (less than 3 m s−1) intensify under relatively weaker VWS than TCs moving at intermediate translational speeds (3–8 m s−1). The probability of RI becomes lower than that of rapid decaying (RD) when the translational speed is larger than 8 m s−1. Most TCs tend to decay when the translational speed is larger than 12 m s−1 regardless of the shear condition.

The Predictability of Idealized Tropical Cyclones in Environments With Time‐Varying Vertical Wind Shear

“…Figure is the same as Figure except that it depicts time series for the ensemble of TCs exposed to SUS phase‐2 profiles (hereafter the SUS ensemble). TCs in the SUS ensemble become stronger during phase‐2 than those in the DDS ensemble, with the ensemble mean MSLP reaching a lower value of 979 hPa at 85 h. The lower mean pressure of TCs in the SUS ensemble supports the hypothesis that upper level shear is less detrimental to intensification (Elsberry & Jeffries, ; Finocchio et al, ; Wang et al, ). The maximum MSLP standard deviation of 4.7 hPa, which occurs at 83 h, is 41% smaller than the maximum in the DDS ensemble.…”

Copolarized and Cross‐Polarized SAR Measurements for High‐Resolution Description of Major Hurricane Wind Structures: Application to Irma Category 5 Hurricane

“…RMW is a key parameter in many parametric vortex models (Deppermann, ; Holland, ; Holland et al, ; Willoughby & Rahn, ; Wood & White, ), and these models are routinely used to derive storm surge and risk models (Lin & Chavas, , and references therein). In addition, the location of the RMW with respect to convective heating has been shown to influence the response of the TC secondary circulation (Schubert & Hack, ) and thus is potentially important for the short‐term forecasting of intensity change (Carrasco et al, ; Wang et al, ). Finally, SAR data could be used to study, in detail, the existence and formation of secondary eyewall features and eyewall replacement cycles (see Kossin & Sitkowski, and references within), which are often monitored using ice scattering signals from microwave imagers.…”

An Ensemble Approach to Investigate Tropical Cyclone Intensification in Sheared Environments. Part II: Ophelia (2011)

“…Another possible explanation relies on the profile of environmental winds; while Katia experienced substantial shear in the lower troposphere (between 850 and 600 hPa), Ophelia experienced substantial shear in the upper troposphere (between 600 and 200 hPa). Recent work by Wang et al (2015) suggests that shear in the lower troposphere can be more disruptive for TC intensity than shear in the upper troposphere.…”