Landfall In China Research Articles

Numerical simulation of size contraction of Typhoon Cempaka (2021)

In 2021, Cempaka, a tiny tropical cyclone, made landfall in China. As the TC intensified prior to landfall, the tropical cyclone size measured with precipitation decreased significantly. A numerical simulation was conducted to examine the possible processes modulating the storm size. Azimuthally mean potential vorticity (PV) was found to decrease mainly in the middle to upper troposphere between 50- and 80-km radii. The PV budget results indicate that the advection and generation of mean PV associated with asymmetric processes, rather than the symmetric processes, primarily contributed to the decrease in mean PV. These asymmetric processes leading to a negative PV tendency were likely associated with inactive outer rainbands. In contrast, the tangential winds simultaneously expanded radially outward, possibly related to inner-core diabatic heating. The findings here emphasize the importance of outer rainband activity in tropical cyclone size change.摘要2021年台风“查帕卡”增强过程中风场向外扩张, 但卫星云图显示降水范围减小. 高分辨率数值模拟结果显示, “查帕卡”降水范围减小对应着50-80km半径处对流层中层位涡的减小. 位涡诊断结果表明, 非对称过程是导致上述位涡减小的关键物理过程, 而非对称过程主要同外雨带活动减弱有关. 上述结果强调了外雨带活动对热带气旋尺度变化的潜在重要影响.

Slower-decaying tropical cyclones produce heavier precipitation over China

The post-landfall decay of tropical cyclones (TC) is often closely linked to the magnitude of damage to the environment, properties, and the loss of human lives. Despite growing interest in how climate change affects TC decay, data uncertainties still prevent a consensus on changes in TC decay rates and related precipitation. Here, after strict data-quality control, we show that the rate of decay of TCs after making landfall in China has significantly slowed down by 45% from 1967 to 2018. We find that, except the warmer sea surface temperature, the eastward shift of TC landfall locations also contributes to the slowdown of TC decay over China. That is TCs making landfall in eastern mainland China (EC) decay slower than that in southern mainland China (SC), and the eastward shift of TCs landfall locations causes more TCs landfalling in EC with slower decay rate. TCs making landfall in EC last longer at sea, carry more moisture upon landfall, and have more favorable dynamic and thermodynamic conditions sustaining them after landfall. Observational evidence shows that the decay of TC-induced precipitation amount and intensity within 48 h of landfall is positively related to the decay rate of landfalling TCs. The significant increase in TC-induced precipitation over the long term, due to the slower decay of landfalling TCs, increases flood risks in China’s coastal areas. Our results highlight evidence of a slowdown in TC decay rates at the regional scale. These findings provide scientific support for the need for better flood management and adaptation strategies in coastal areas under the threat of greater TC-induced precipitation.

Detecting the impact of climate change on tropical cyclones in Southern China

Abstract It is well known that tropical cyclones (TCs) making landfall in Southern China (SC) account for more than half of all TCs making landfall in China. Therefore, it is important to have an in-depth understanding of the activities of TCs in SC under climate warming. Our results show that there have been no significant changes in the frequency and duration of these TCs, but their intensities have unexpectedly decreased by ~20% since 1980, which is inconsistent with the previous understanding that climate change increases TC intensity. The results consistently show a significant decrease in the different TC intensity percentiles, which is related to the intensity distribution that shows a significant decrease in the proportion of tropical storms and a significant increase in the proportion of tropical depressions, as well as a slight decrease in the proportion of category 1-2. Because of the locations of those TCs activity show a clear shoreward migration tendency, indicating that land friction can suppress TC intensification, so that TC intensity has weakened. In addition, results also suggest that TC development is strongly suppressed and is mainly related to the enhancement of atmospheric stability, vertical wind shear and subtropical high under global warming. These results are quite different from the previous understanding of the changes in TC intensity under global warming. Such knowledge can help us better understand the relationship between climate change and the impact of TC activity at the regional scale.

Long-range prediction of the tropical cyclone frequency landfalling in China using thermocline temperature anomalies at different longitudes

The landfalls of the tropical cyclone (TC) along the coast of China have caused huge economic damages. There are approximately nine TC landfalls in China every year. It will be beneficial if the landfall frequency can be predicted in advance. Inspired by the study of Sparks and Toumi (Commun Earth Environ, 30-1-2020), six datasets, including four ocean reanalyses and two object analyses from 1993 to 2019, are employed to study the consistency in the relationship between the thermocline temperature anomalies at different longitudes and the frequency of TC landfalls along the coastal areas of China (South China, East China, and the whole of China). The thermocline temperature anomalies at different longitudes are tested in order to confirm our hypothesis that the eastward and westward transports of ocean heat from the warm pool are the causes of the significant correlations. The results show some significant correlations at various longitudes, and the temperature anomalies can predict the TC landfall frequency for several months or longer. Further study also shows the close relationship between the ocean heat transport and the sea surface temperature anomalies at the genesis locations of TC landfalls. The locations of the western Pacific subtropical high (WPSH) during high-frequency TC landfall years also show favorable spatial patterns to the TC landfall in South China and East China, respectively. In years with a high TC frequency in South China, the westward displacement of the WPSH ridge steers TC toward South China, while during high-frequency TC landfall years in East China, WPSH is located further north, and the westward extension of the ridge is in close proximity to the East China Sea.

An Observational Study of Short‐Cycle Lightning Outbreaks in the Inner Core of Typhoon Hato (2017) Before Landfall

AbstractThis study analyzes microphysical signatures relevant to the short‐cycle lightning activity in the inner core of Typhoon Hato (2017) before landfall in China. Observations reveal that the lightning bursts were accompanied by enhanced inner‐core convection with a behavior cycle of about 3 hr. The coupling between wavenumber‐2 vortex Rossby waves (VRWs) and shear‐forced convective asymmetries resulted in a local updraft enhancement. Furthermore, supercooled liquid water droplets invigorated a striking enhancement of graupel via riming immediately above the freezing level, further enhancing charge separation and lightning generation outside the eyewall. Furthermore, when similar phase‐locking was associated with other propagating VRWs, graupel and updraft volumes were significantly boosted, leading to short‐cycle lightning outbreaks in the inner core.

Characteristics of the tropical cyclones before making landfall in China

AbstractTropical cyclones (TCs) before landfall deserve great concerns, which directly affect the following forecasts and alarm‐issuing. In 1949–2021, nearly 29% of the total number of TCs that originated over the western North Pacific (WNP) and the South China Sea (SCS) made landfall in China. Of them, those from the WNP display a significantly lower (higher) ratio of making landfall over China (south China) in (the second year after) El Niño years. At 48 h before landfall, the TC centers display significant inter‐annual variations in zonal direction, but only those from the WNP additionally show significant inter‐decadal variations in meridional direction, which are probably attributed to the El Niño–Southern Oscillation and the large‐scale environment from both the ocean and the atmosphere. Once they move into a distance of ~660 km (~900 km) away from the south and southeast (east) coastlines of China, the probability of making landfall in the subsequent 24 h is increasing. In the 3 days before landfall, TCs show decreasing (increasing) uncertainty in translation speed (moving direction) as they moved close to the land, which is regardless of either the origination or the destination. In general, a moving direction of west‐northwestward dominates the majority of TCs if they originated from the WNP, which exhibits a clockwise rotation trend and tends to move faster as they approached the land. In comparison, those TCs originated from and stayed over the SCS show the largest uncertainty of moving direction and the most frequent abnormal tracks. For intensity (maximum wind speed), those originated from the WNP are generally stronger than those from the SCS. Their intensities vary in a range of −5 m s−1 to 5 m s−1 in each connective 6 h in the 3 days before landfall, of which the TCs made landfall in the east China display the largest uncertainty. In particular, great attention should be paid to the TCs originating from the WNP and approaching the southeast China in the future, in which the rapid intensification occurred with the most frequency but with a significantly lower occurrence in the second year after the El Niño years in the period investigated.

El Niño Onset Time Affects the Intensity of Landfalling Tropical Cyclones in China

In this work, we studied the influence of spring (SP) and summer (SU) El Niño events on the landfalling tropical cyclones (TCs) in China. The results showed that compared to SU El Niño years, the average latitude of the landfalling TCs in SP El Niño years shifted significantly southward and that the average TC intensity was significantly stronger, especially in the post-landfall period. Additionally, more severe tropical storm-level TCs generated over the South China Sea made landfall in China. Meanwhile, in SP El Niño years, landfalling TCs in southern China had a greater landfall intensity, but landfalling TCs in eastern China were the opposite. These changes in TC intensity during the SP El Niño years could be attributed to more favorable dynamical and thermodynamical conditions, which are beneficial for maintaining TC intensity and duration after landfall. These results could have important implications for an in-depth understanding of TC activities, as well as TC disaster prevention and mitigation.

Biogenic emissions-related ozone enhancement in two major city clusters during a typical typhoon process

Typhoons could influence air quality via multiple chemical and physical process and has attracted much scientific attention. A typical typhoon, In-Fa, passed through Yangtze River Delta (YRD) and Jing-Jin-Ji (JJJ) after it made a landfall in China. Under such influences, two city clusters both experienced high ozone (O3) concentrations, with JJJ about 5 days earlier than YRD. Data from several environmental monitoring sites and three regional sites indicated that cross-regional transport and biogenic emissions both played an important role in O3 formation. During the typhoon process, O3 precursors were first transported from YRD and its surrounding areas to JJJ due to the summer monsoon. After that, air masses from northern China returned to YRD due to the peripheral winds of the typhoon. High O3 was concentrated in downwind regions, causing fast secondary formation. The peripheral winds and downdrafts of typhoon led to high temperature and stagnant weather, favorable for biogenic emissions. Observed isoprene concentration was doubled. The ratio of isoprene to VOCs also increased by around 5%. The modeling results showed the contribution of BVOCs to O3 could reach 10 ppb in JJJ when the typhoon made its landfall in YRD. When the typhoon moved to JJJ, the cross-transport of air masses from northern China to YRD contributed half of biogenic-emission-related O3. Our research extends the knowledge into the importance of biogenic emissions to O3 and cross-regional transport during a typhoon process.

Unexpected high contribution of in-cloud wet scavenging to nitrogen deposition induced by pumping effect of typhoon landfall in China

Atmospheric nitrogen deposition has large eco-environmental effects such as ocean acidification, eutrophication in coastal areas. However, knowledge of the source and the pathway of N deposition in coastal areas is limited, especially during tropical storms, hindering the accurate quantification of how anthropogenic activities influence the ocean ecosystem. In this study, the Nested Air Quality Prediction Modeling System was used to investigate the wet deposition of N induced by typhoon Hagupit over eastern coastal China from an in- and below-cloud process perspective. Our results reveal for the first time an enhancement mechanism of N deposition related to the ‘pumping effect’ of the typhoon. Different from the non-typhoon conditions, air pollutants in the typhoon-affected regions were pumped into the higher altitudes and deposited via the in-cloud scavenging process in the moving path of the typhoon-affected regions. This study updates our understanding of the source–receptor relationship on atmospheric wet deposition caused by tropical cyclones.

Improving Analysis and Prediction of Tropical Cyclones by Assimilating Radar and GNSS-R Wind Observations: Ensemble Data Assimilation and Observing System Simulation Experiments Using a Coupled Atmosphere–Ocean Model

Abstract This study investigates the impact of assimilating ground-based radar reflectivity and wind data on tropical cyclone (TC) intensity prediction. The effect on a high-impact TC in the western North Pacific region that penetrated the Bashi Channel is examined. A multiscale correction based on the successive covariance localization (SCL) method is adopted to improve the analysis and forecast performance. In addition, GNSS-R wind speed is assimilated jointly in the rapid update assimilation framework to complement the TC boundary layer where radar data are limited. Model experiments are conducted and evaluated using the observing system simulation experiments (OSSEs) framework with a coupled atmosphere–ocean model nature run. Taking the experiment without data assimilation as the baseline, assimilating the radar data with the standard localization and SCL methods reduces the wind speed analysis error by 12% and 44%, respectively. The SCL method dominates the improvement in TC intensity prediction with a lead time longer than 2 days and the TC’s peak intensity forecast is improved by 18 hPa. The additional assimilation of the GNSS-R wind speed observation further reduces the wind speed error in the low-level analysis by 12% and 5% under the standard and SCL radar assimilation framework, respectively. GNSS-R wind assimilation leads to a further 6-hPa improvement in TC’s peak intensity. However, the sampling error introduced by the SCL method restrains the effect of GNSS-R assimilation. Sensitivity experiments with different GNSS-R data arrangements show that better GNSS-R wind coverage and additional wind direction information can further improve the TC analysis. Significance Statement Tropical cyclone (TC) intensity prediction over the western North Pacific (WNP) region remains a significant challenge due to limited observations. This study aims to improve the TC intensity prediction in WNP by assimilating the ground-based radar data using a multiscale correction framework and incorporating with the satellite ocean surface wind speed observation. We particularly focus on a high-impact TC like Typhoon Hato (2017), which penetrated the Bashi Channel and later made landfall in China, causing great damage. Our results showed that the assimilation strategy improved the TC intensity prediction for a lead time longer than 2 days. These results demonstrate the great potential of these observations and can provide guidance for future applications in operation centers.

Changes of Tropical Cyclones Landfalling in China From 1979 to 2018

AbstractThis study investigates the long‐term changes of tropical cyclones (TCs) that originated over the western North Pacific (WNP) and made landfall in China from 1979 to 2018. The TC best track data sets from the three primary weather agencies, the China Meteorological Administration (CMA), the Japan Meteorological Agency (JMA), and the Joint Typhoon Warning Center (JTWC), and the TCs landfall data from the CMA are used in this study. Trend analysis of the mean locations of the TCs' lifetime maximum intensity (LMI) suggests that the locations of the LMI of TCs have moved closer to the coast gradually. This shift may be associated with a landward migration of TC genesis. The changes in TC LMI possibly contribute to the slight increase in the TCs' landfall intensity and the significant growth of TCs' overland duration. Further analyses indicate that all these changes may be mainly due to both dynamic and thermodynamic conditions in the WNP, which tend to be more favorable for the formation and development of TCs, and some of the favorable conditions have shifted toward the land during the 40 years.

Lightning Distribution in Tropical Cyclones Making Landfall in China

Lightning data from the World Wide Lightning Location Network (WWLLN) are used to document the lightning characteristics in tropical cyclones (TCs) making landfall in China. The landfall period is confined to 48 h prior to and after landfall (t-24∼t+24). Data from a total of 74 TCs are collected from 2010 to 2020, providing 3,293 individual time periods (1-h periods). To examine the radial and asymmetry distributions as a function of TC intensity, landing location, and vertical wind shear, the dataset is classified into two intensity categories, three shear groups, and four landing locations. WWLLN detected lightning activity in all TCs during the 48-h landfall, with lightning rates most frequently appearing between 250 and 600 str h−1. Extreme hourly lightning rates of 3,154 str h−1 and 4,426 str h−1 are observed in the inner core in Tropical Storm Cimaron (2013) and the outer rainbands in Severe Typhoon Matmo (2014), respectively, comparable to lightning activity in mesoscale convection systems on land. TCs landing in Guangdong and Hainan have the largest peak lightning rates, while those landing in Zhejiang and Shanghai show the lowest lightning rates. The maximum lightning density is found in the inner-core region of weak TCs (<32.7 m s−1) that are located approximately 100–200 km away from the coastline. The radial distribution of lightning density at landing stages is consistent with that at mature stages when TCs are over the ocean. However, there is a shift in the lightning maximum from the inner core prior to landfall (t-24∼t0) to the outer rainbands after landfall (t0∼t+24), indicating the effects of dry continental air intrusion and the enhanced surface frictional convergence. Vertical wind shear is the dominant factor in producing lightning and convective asymmetry for TCs landing in all locations. Lightning asymmetries are enhanced with the increase in shear magnitude from low (<5 m s−1) to moderate (5–10 m s−1) and high (>10 m s−1) shear environments, both in weak and strong TCs (≥32.7 m s−1).

Microphysical Characteristics of the Phase‐Locking VRW‐Induced Asymmetric Convection in the Outer Eyewall of Super Typhoon Lekima (2019)

AbstractMicrophysical signatures relevant to the asymmetric convection in the outer eyewall of Super Typhoon Lekima (2019) before its landfall in China were analyzed from ground‐based radar observations. The results indicate that the microphysical characteristics varied in quadrants. In the upshear‐left outer eyewall, the convection was deepened on the inner edge due to the phase locking between vortex Rossby waves (VRWs), and warm rain was the predominant process contributing to the enhancement of rainfall. In contrast, the strongest precipitation occurred on the outer edge of the upshear‐right outer eyewall. In this region, exuberant riming processes and graupel formation prevailed above the melting layer due to the strongest and more outward tilted updrafts induced by the phase locking between the VRWs. A good deal of graupel melted into raindrops, along with significant accretion processes, produced intense rainfall with larger drop sizes.

Impacts of New Implementing Strategies for Surface and Model Physics Perturbations in TREPS on Forecasts of Landfalling Tropical Cyclones

To improve the ensemble prediction system of the tropical regional atmosphere model for the South China Sea (TREPS) in predicting landfalling tropical cyclones (TCs), the impacts of three new implementing strategies for surface and model physics perturbations in TREPS were evaluated for 19 TCs making landfall in China during 2014–16. For sea surface temperature (SST) perturbations, spatially uncorrelated random perturbations were replaced with spatially correlated ones. The multiplier f, which is used to form perturbed tendency in the Stochastically Perturbed Parameterization Tendency (SPPT) scheme, was inflated in regions with evident convective activity (f-inflated SPPT). Lastly, the Stochastically Perturbed Parameterization (SPP) scheme with 14 perturbed parameters selected from the planetary boundary layer, surface layer, microphysics, and cumulus convection parameterizations was added. Overall, all these methods improved forecasts more significantly for non-intensifying than intensifying TCs. Compared with f-inflated SPPT, the spatially correlated SST perturbations generally showed comparable performance but were more (less) skillful for intensifying (non-intensifying) TCs. The advantages of the spatially correlated SST perturbations and f-inflated SPPT were mainly present in the deterministic guidance for both TC track and wind and in the probabilistic guidance for reliability of wind. For intensifying TCs, adding SPP led to mixed impacts with significant improvements in probability-matched mean of modest winds and in probabilistic forecasts of rainfall; while for non-intensifying TCs, adding SPP frequently led to positive impacts on the deterministic guidance for track, intensity, strong winds, and moderate rainfall and on the probabilistic guidance for wind and discrimination of rainfall.

Typhoon Hato's precipitation characteristics based on PERSIANN

Heavy precipitation induced by typhoons is the main driver of catastrophic flooding, and studying precipitation patterns is important for flood forecasting and early warning. Studying the space-time characteristics of heavy precipitation induced by typhoons requires a large range of observation data that cannot be obtained by ground-based rain gauge networks. Satellite-based estimation provides large domains of precipitation with high space-time resolution, facilitating the analysis of heavy precipitation patterns induced by typhoons. In this study, Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks (PERSIANN) satellite data were used to study the temporal and spatial features of precipitation induced by Typhoon Hato, which was the strongest typhoon of 2017 to make landfall in China. The results show that rainfall on the land lasted for six days from the typhoon making landfall to disappearing, reaching the maximum when the typhoon made landfall. Hato produced extremely high accumulated rainfall in South China, almost 300 mm in Guangdong Province and Guangxi Zhuang Autonomous Region and 260 mm in Hainan Province. The rainfall process was separated into three stages and rainfall was the focus in the second stage (5 h before making landfall to 35 h after making landfall).

Drastic change in dynamics as Typhoon Lekima experiences an eyewall replacement cycle

Why does the 1909 typhoon, Lekima, become so destructive after making landfall in China? Using a newly developed mathematical apparatus, the multiscale window transform (MWT), and the MWT-based localized mutliscale energetics analysis and theory of canonical transfer, this study is intended to give a partial answer from a dynamical point of view. The ECMWF reanalysis fields are first reconstructed onto the background window, the TC-scale window, and the convection-scale window. A localized energetics analysis is then performed, which reveals to us distinctly different scenarios before and after August 8–9, 2019, when an eyewall replacement cycle takes place. Before that, the energy supply in the upper layer is mainly via a strong upper layer-limited baroclinic instability; the available potential energy thus-gained is then converted into the TC-scale kinetic energy, with a portion to fuel Lekima’s upper part, another portion carried downward via pressure work flux to maintain the cyclone’s lower part. After the eyewall replacement cycle, a drastic change in dynamics occurs. First, the pressure work is greatly increased in magnitude. A positive baroclinic transfer almost spreads throughout the troposphere, and so does barotropic transfer; in other words, the whole air column is now both barotropically and baroclinically unstable. These newly occurred instabilities help compensate the increasing consumption of the TC-scale kinetic energy, and hence help counteract the dissipation of Lekima after making landfalls.

Quantifying interagency differences in intensity estimations of Super Typhoon Lekima (2019)

There were significant discrepancies in the intensity estimations of Super Typhoon Lekima (2019) among the China Meteorological Administration (CMA), the United States Joint Typhoon Warning Center (JTWC), and the Japan Meteorological Agency (JMA) data sets, with a maximum difference of over 12 m/s and 16 m/s between the JTWC data set and the CMA and JMA data sets, respectively. During the intensification phase, disagreement on the maximum sustained wind (MSW) between these agencies was due to the use of different conversion tables for the current intensity number (CI) estimated by Dvorak technique-MSW. In addition, CI discrepancies and different available observational data were also important contributors to the different intensities estimated during the Lekima’s decay phase before landfall. The ability of various methods to minimize these discrepancies was evaluated in this study. Both the linear factor multiplication method and the remapping method using the same CI-MSW conversion table have substantially abilities to reduce intensity discrepancies, with the latter method being more effective. However, these improvements only hold for the intensification phase in the ocean. The CMA data set had more complete and accurate intensity estimations when Lekima made landfall in China. After its landfall, the intensity estimate of the CMA was comparable to that of the JMA, which differed greatly from that of the JTWC.

Impact of the Pacific Meridional Mode on landfalling tropical cyclone frequency in China

AbstractThis study identifies a significant positive correlation between the Pacific Meridional Mode (PMM) index and frequency of tropical cyclones (TCs) landfalling in China during peak TC season (June–November) of the period 1977–2018. This interannual association is independent of two types of El Niño–Southern Oscillation. Large‐scale circulation over the western North Pacific (WNP) modulated by PMM can affect TC genesis location/frequency and steering flow that directly determine TC landfalls in China. During the positive PMM phase, anomalous off‐equatorial heating over the eastern North Pacific can induce anomalous low‐level cyclonic circulation and upper‐level anticyclonic circulation over most of the main development region in the WNP, as a Gill‐type Rossby wave response. The resultant larger low‐level relative vorticity and weaker vertical wind shear are conducive to the formation of more TCs over the main development region. The anomalous easterly steering flow in the north flank of the anomalous low‐level cyclonic circulation is favourable for more TCs moving westward/northwestward and making landfall in China. The physical mechanism for the impact of PMM on large‐scale circulation over the WNP is verified by numerical experiments using the Community Atmospheric Model. The PMM index is demonstrated to be a crucial predictor for landfalling TC frequency in China in statistical seasonal prediction models.

Predominant factors of disaster caused by tropical cyclones in South China coast and implications for early warning systems

Predicting disastrous wind and rainfall associated with tropical cyclones (TCs) is critical to prevent and mitigate the casualties and damage of TCs. The studied warning area was chosen with a radius of 800 km centered on Hong Kong in which the tracks of TCs making landfall in China are concentrated. In general, the number of TCs making landfall decreased but landfall locations and intensities of TCs increased since 1990. Our results suggested minimum sea level pressure (MSLP) in TC affected areas was the predominant disaster-warning factor and indicator for the resulting risks and damages of TCs in 1975–2017. The MSLP of 990 hPa monitored in a TC affected area was a threshold for severe impacts and prediction of strong wind and heavy rainfall. Early warning using a combination of MSLP and the nearest approach distance of TCs (MSLP of 990 hPa for distance of 100 km) outperformed the current warning system based on wind speed, often providing more timely warning and reducing the false warnings.

Monsoonal Influences on Offshore Rapid Intensification of Landfalling Typhoons in a Sheared Environment over the South China Sea

Abstract Tropical cyclones (TCs) formed in the western North Pacific and South China Sea can undergo rapid intensification (RI) shortly before making landfall in China. Forecasting such offshore RI is a great challenge in operations. In this study the offshore RI events in a sheared environment are examined for TCs that made landfall in China during 1979–2017. It is found that there were only three offshore RI events in a sheared environment, all of which occurred to the south of Hainan Island within the monsoon trough in early to mid-July, coinciding with the termination of the mei-yu season. The specific geographic location and timing of the occurrence of the offshore RI in the sheared environment is associated with the adjustment of the East Asia summer monsoon system when the mei-yu season terminates in the Yangtze River valley. In addition to the adjustment favorable for TC intensification by enhancing the TC–trough interaction in the upper troposphere, this study suggests that two environmental factors also contribute to the offshore RI over the South China Sea in a sheared environment. One is the intrusion of dry air associated with the western North Pacific subtropical high (WNPSH) and the other is the penetration of the water vapor flux associated with the monsoon surge. The adjustment of the East Asia summer monsoon system allows the water vapor flux of the monsoon surge to penetrate the TC circulation and prevents the dry air of the WNPSH from intruding into the TC circulation.