Tropical Cyclone Landfall Research Articles

Is the tropical cyclone surge in Shanghai more sensitive to landfall location or intensity change?

AbstractIt has been shown that the proportion of intense tropical cyclones (TCs) has been increasing together with a poleward migration of TC track. However, their relative importance to TC surge at landfall remains unknown. Here we examine the sensitivity of TC surge in Shanghai to landfall location and intensity with a new dynamical modelling framework. We find a surge sensitivity of 0.8 m (°N)−1 to landfall location, and 0.1 m (m s−1)−1 to wind speed in Shanghai during landfall. The landfall location and intensity are comparably important to surge variation. However, based on a plausible range of reported trends of TC poleward migration and intensity, the potential surge hazard due to poleward migration is estimated to be about three times larger than that by intensity change. The long‐term surge risk in Shanghai is therefore substantially more sensitive to changes of TC track and landfall location than intensity. This may also be true elsewhere and in the future.

Environmental analysis on the first documented tornado outbreak in China

AbstractThis study presents an analysis on the storm environmental features during the first recorded tornado outbreak in the modern history of China on August 13–14, 2018. Eleven reported tornadoes were spawned within a 20‐hr period by Typhoon Yagi (1814) during its dissipating stage after its landfall. They primarily formed when Yagi was at a relatively weak intensity. Six tornadoes were generated after that Yagi had lost its intensity as a tropical depression. These tornadoes were mainly located in the northeast quadrant with respect to the typhoon center. Specifically, they were concentrated in the overlapping region of the large storm relative helicity (SRH) and large entraining convective available potential energy (E‐CAPE) that considers the effects of the environmental air entrainment. The intrusion of midlevel dry air was responsible for the spatial pattern of large‐value E‐CAPE. Special focus was further put into the dynamical diagnosis of the cause that the maxima in SRH were distributed in Yagi's northeast sector. On cylindrical coordinates, the northeast quadrant was characterized by the strongest upward increase in the radial velocity in a layer of 950–700 hPa, which resulted from the interaction between the typhoon circulation and the subtropical high and a midlevel trough. The resultant in‐up‐out radial wind profile contributed to the large helicity in the northeast quadrant. In the lowest 50 hPa layer, the helicity was mainly owed to the upward increase in the tangential velocity associated with typhoon vortex. The diagnoses of the atmospheric environment for the tornado outbreak in this case may provide additional benefit for assessing the tornado risk within landfalling tropical cyclones in China.

Observed Vertical Structure of Precipitation Influenced by Dry Air for Landfalling Tropical Cyclones Over China

AbstractThe vertical structure of precipitation and its evolution during midlevel dry‐air intrusion (DAI) for landfalling tropical cyclones (LTCs) over China in the past 10 years were examined using several observed Tropical Rainfall Measuring Mission (TRMM) PR products and a reanalysis data set. We show that in the outer region where the environmental midlevel dry air intrudes more easily, the process of environmental DAI has an important effect on the vertical structure and precipitation of LTCs through promoting substantially stratiform precipitation, while inhibiting infrequent intense convective precipitation. Although the total mean rain rate does not change much during the DAI period, both the mean rain rate and area of stratiform precipitation are almost doubled, while the convective precipitation halves compared to the situation prior to the DAI period. Also, the vertical structure of precipitation relative to the vertical wind shear (VWS) is modulated by the dry air, with a clear stratiform precipitation structure in the DAI region, though the dry‐air distribution of LTCs does not depend on the direction of the VWS but rather on the synoptic environmental collocation. Further analysis shows that the mid‐level DAI is favorable to the generation of stratiform precipitation through producing moderate midlevel convergence and less intense low‐level subsidence, which contribute to the mid‐level spin‐up without spinning down the low‐level circulation. At the same time, it helps in maintaining the uniform stratiform precipitation above the melting layer and homogenizing the low‐level circulation, and thus boosts the development of stratiform precipitation in intensity and area in the outer region.

Spatial and Temporal Variation Characteristics of the Intensity of Landfall Tropical Cyclones in China

Based on the tropical cyclone data of the United States Joint Typhoon Center, this paper analyses the characteristics of the temporal and spatial changes of tropical cyclones that landed in China from 1951 to 2015. The conclusions are as follows: (1) The frequency of landings showed a slow upward trend from 1951 to the early 1990s, and showed a slow downward trend from the late 1990s to 2015. In 1988, it changed from a low period to a high period. (2) Tropical cyclones are mainly distributed in the range of 130-140°E, 10-15°N east of the Philippine Islands, and the northeastern part of the South China Sea. The spatial distribution of the first eigenvector of the source frequency EOF is basically the same as the multi-year spatial distribution. From the time coefficient of the first mode, the change trend of the concentrated distribution has undergone a process of strengthening-weakening. From the perspective of the spatial distribution of the second mode, the source frequencies in the Northwest Pacific and the South China Sea have opposite spatial distribution characteristics in the latitude direction. (3) One of the main tracks of landfall tropical cyclones is westward from the tropical Pacific to the Philippine Sea and South China Sea, and the other from the tropical Pacific to the northwest to South Korea and Japan, affecting the area near the coast of East Asia. The spatial distribution of the first eigenvector of the track frequency EOF is basically the same as that of the multi-year spatial distribution, and the spatial distribution of the second mode has a positive-negative opposite spatial distribution characteristic in the meridian direction.

The Use of the Conway–Maxwell–Poisson in the Seasonal Forecasting of Tropical Cyclones

AbstractThe Conway–Maxwell–Poisson distribution improves the precision with which seasonal counts of tropical cyclones may be modeled. Conventionally the Poisson is used, which assumes that the formation and transit of tropical cyclones is the result of a Poisson process, such that their frequency distribution has equal mean and variance (“equi-dispersion”). However, earlier studies of observed records have sometimes found overdispersion, where the variance exceeds the mean, indicating that tropical cyclones are clustered in particular years. The evidence presented here demonstrates that at least some of this overdispersion arises from observational inhomogeneities. Once this is removed, and particularly near the coasts, there is evidence for equi-dispersion or underdispersion. To more accurately model numbers of tropical cyclones, we investigate the use of the Conway–Maxwell–Poisson as an alternative to the Poisson that represents any dispersion characteristic. An example is given for East China where using it improves the skill of a prototype seasonal forecast of tropical cyclone landfall.

Correction to: Spatiotemporal Analysis of Tropical Cyclone Landfalls in Northern Bay of Bengal, India and Bangladesh

Correction to: Spatiotemporal Analysis of Tropical Cyclone Landfalls in Northern Bay of Bengal, India and Bangladesh

Birth of a cold core in tropical cyclones past landfall

What happens to a tropical cyclone past landfall? Per the prevailing theory, tropical cyclones past landfall decay via a straightforward process in which thermodynamics plays no role. We show, contrary to this theory, that thermodynamics is crucially important and propose a conceptual framework for the post-landfall phase, culminating in the surprising discovery of the birth of a cold core. In addition to its significance for our understanding of the post-landfall phase, the birth of a cold core bears directly on the current forecasting methods for extreme weather conditions triggered by a landfalling tropical cyclone.

Combined Effect of the PDO and ENSO on the Date of the First Tropical Cyclone Landfall in Continental East Asia

AbstractThe date of the first tropical cyclone (TC) landfall (DFTCL) is important for TC disaster prevention. This study analyzes the variation in the characteristics of the DFTCL in continental East Asia and investigates the possible effect of the Pacific Decadal Oscillation (PDO) and the El Niño‐Southern Oscillation (ENSO) on the DFTCL. Results show that the combined effect of the PDO and ENSO plays an important role in whether TC landfall occurs relatively earlier or later. During negative PDO phases, the DFTCL is impacted significantly by ENSO events. TCs tend to make landfall later (earlier) in the years following El Niño (La Niña). However, little influence is noticeable for the ENSO events during positive PDO phases. The combined effect is possibly associated with the anomalous anticyclone (cyclone) in the western North Pacific (South China Sea) which is modulated by different PDO phases asymmetrically. During negative PDO phases, the tropical Indian Ocean (TIO) has a strong response to El Niño events in winter. The warm anomaly persists in the following months until early summer. This induces the anomalous anticyclone in the western North Pacific which is enhanced by the anomalous meridional circulation. The anomalous anticyclone can suppress TC genesis and landfall. On the other hand, the TIO has a significant cooling response to La Niña events and induces the anomalous cyclone near the South China Sea. The anomalous cyclone favors earlier than usual TC genesis and landfall. However, this relationship cannot be detected in the positive PDO phase.

Strongly Coupled Assimilation of a Hypothetical Ocean Current Observing Network within a Regional Ocean–Atmosphere Coupled Model: An OSSE Case Study of Typhoon Hato

AbstractThe forecast of tropical cyclone (TC) intensity is a significant challenge. In this study, we showcase the impact of strongly coupled data assimilation with hypothetical ocean currents on analyses and forecasts of Typhoon Hato (2017). Several observation simulation system experiments (OSSE) were undertaken with a regional coupled ocean–atmosphere model. We assimilated combinations of (or individually) a hypothetical coastal current HF radar network, a dense array of drifter floats, and minimum sea level pressure. During the assimilation, instant updates of many important atmospheric variables (winds and pressure) are achieved from the assimilation of ocean current observations using the cross-domain error covariance, significantly improving the track and intensity analysis of Typhoon Hato. Relative to a control experiment (with no assimilation), the error of minimum pressure decreased by up to 13 hPa (4 hPa/57% on average). The maximum wind speed error decreased by up to 18 kt (5 kt/41% on average) (1 kt ≈ 0.5 m s−1). By contrast, weakly coupled implementations cannot match these reductions (10% on average). Although traditional atmospheric observations were not assimilated, such improvements indicate that there is considerable potential in assimilating ocean currents from coastal HF radar and surface drifters within a strongly coupled framework for intense landfalling TCs.

Spatial variations of North Atlantic landfalling tropical cyclone wind speed decay over the continental United States

AbstractUnderstanding tropical cyclone wind speed decay during the post-landfall stage is critical for inland hazard preparation. This paper examines the spatial variation of wind speed decay of tropical cyclones over the continental United States. We find that tropical cyclones making landfall over the Gulf Coast decay faster within the first 24 hours after landfall than those making landfall over the Atlantic East Coast. The variation of the decay rate over the Gulf Coast remains larger than that over the Atlantic East Coast for tropical cyclones that had made landfall more than 24 hours prior. Besides an average weaker tropical cyclone landfall intensity, the near-parallel trajectory and the proximity of storms to the coastline also help to explain the slower post-landfall wind speed decay for Atlantic East Coast landfalling tropical cyclones. Tropical cyclones crossing the Florida peninsula only slowly weaken after landfall, with an average of less than 20% post-landfall wind speed drop while transiting the state. The existence of these spatial variations also brings into question the utility of a uniform wind decay model. While weak intensity decay over the Florida peninsula is well estimated by the uniform wind decay model, the error from the uniform wind decay model increases with tropical cyclones making direct landfall more parallel to the Atlantic East Coast. The underestimation of inland wind speed by the uniform wind decay model found over the western Gulf Coast brings attention to the role of land-air interactions in the decay of inland tropical cyclones.

Impact of the Monsoonal Surge on Extreme Rainfall of Landfalling Tropical Cyclones

A comparative analysis and quantitative diagnosis has been conducted of extreme rainfall associated with landfalling tropical cyclones (ERLTC) and non-extreme rainfall (NERLTC) using the dynamic composite analysis method. Reanalysis data and the tropical cyclone precipitation dataset derived from the objective synoptic analysis technique were used. Results show that the vertically integrated water vapor transport (Qvt) during the ERLTC is significantly higher than that during the NERLTC. The Qvt reaches a peak 1–2 days before the occurrence of the ERLTC and then decreases rapidly. There is a stronger convergence for both the Qvt and the horizontal wind field during the ERLTC. The Qvt convergence and the wind field convergence are mainly confined to the lower troposphere. The water vapor budget on the four boundaries of the tropical cyclone indicates that water vapor is input through all four boundaries before the occurrence of the ERLTC, whereas water vapor is output continuously from the northern boundary before the occurrence of the NERLTC. The water vapor inflow on both the western and southern boundaries of the ERLTC exceeds that during the NERLTC, mainly as a result of the different intensities of the southwest monsoonal surge in the surrounding environmental field. Within the background of the East Asian summer monsoon, the low-level jet accompanying the southwest monsoonal surge can increase the inflow of water vapor at both the western and southern boundaries during the ERLTC and therefore could enhance the convergence of the horizontal wind field and the water vapor flux, thereby resulting in the ERLTC. On the other hand, the southwest monsoonal surge decreases the zonal mean steering flow, which leads to a slower translation speed for the tropical cyclone associated with the ERLTC. Furthermore, a dynamic monsoon surge index (DMSI) defined here can be simply linked with the ERLTC and could be used as a new predictor for future operational forecasting of ERLTC.

Hydrological Response of the Pampanga River Basin in the Philippines to Intense Tropical Cyclone Rainfall

AbstractThe Philippines is frequently affected by tropical cyclones (TCs), and understanding the flood response of the Pampanga River basin (PRB) from TC-induced rain is needed in effective disaster risk management. As large uncertainties remain in TC rain forecasting, we propose a simple checklist method for flood forecasting of the PRB that depends on the general TC track, season, and accumulated rainfall. To this end, flood events were selected based on the alert, alarm, and critical river height levels established by the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA). Results show that all flood events in the PRB were induced by TCs. All intense TCs that directly traversed the PRB resulted in critical-level floods. These TCs also had the shortest flood onset of 7–27 h from alert to critical level. Flooding from distant landfalling TCs, on the other hand, are dependent on season. TCs traversing north (south) of the PRB induced flooding only during the southwest (northeast) monsoon season. These TCs can raise water levels from alert to critical in 11–48 h. Remote precipitation from non-landfalling TCs can also induce critical-level flooding but with a longer onset time of 59 h. These results indicate that a simple checklist method can serve as a useful tool for flood forecasting in regions with limited data and forecasting resources.

Destructive destruction or creative destruction? Unraveling the effects of tropical cyclones on economic growth

This paper investigates the contemporaneous and long-term effects of tropical cyclones and the related policies on economic growth and associated structural changes. We consider three distinguishing features of tropical cyclones, including wind speed, precipitation, and storm surge height, as well as one policy-related feature of tropical cyclones in Hong Kong—the issuing of the No. 8 signal. Using data from Hong Kong for the period 1980–2018, we show that although tropical cyclone landfalls on the coast of Hong Kong have much higher average wind speeds, wind speed does not have a significant influence on either overall GDP or sectoral GDP. Economic losses from tropical cyclones are driven mainly by the issuing of the No. 8 signal, a climate policy in Hong Kong that suspends daily activities in dangerous tropical cyclone weather. With an average shutdown of 1.87 days due to No. 8 signals, the economic loss is about 0.9 billion U.S. dollars. However, in the long run, the No. 8 signal policy has delayed positive impacts on total GDP and some sectoral growth. Our analysis suggests that at least five years of recovery is necessary for damage attributed to severe tropical cyclones.

Forgotten accounts of tropical cyclones making landfall in Tanzania

Landfalling tropical cyclones are essentially unheard of in Tanzania. It has been suggested that Cyclone Kenneth, which occurred in 2019, was the first tropical cyclone to make landfall in Tanzania. This paper brings to light tropical cyclones that made landfall in Tanzania in 1872 and 1952. We draw on eyewitness accounts and meteorological observations to raise the profile of these seemingly forgotten tropical cyclones, which devastated lives and economic activities. The severe societal impacts, and potential link to climate change, of landfalling tropical cyclones in Tanzania encourages further investigation into the drivers of tropical cyclones in the southwest Indian Ocean.

Observed Shear-Relative Rainfall Asymmetries Associated with Landfalling Tropical Cyclones

This study examines the shear-relative rainfall spatial distribution of tropical cyclones (TCs) during landfall based on the 19-year (1998–2016) TRMM satellite 3B42 rainfall estimate dataset and investigates the role of upper-tropospheric troughs on the rainfall intensity and distribution after TCs make a landfall over the six basins of Atlantic (ATL), eastern and central Pacific (EPA), northwestern Pacific (NWP), northern Indian Ocean (NIO), southern Indian Ocean (SIO), and South Pacific (SPA). The results show that the wavenumber 1 perturbation can contribute ∼ 50% of the total perturbation energy of total TC rainfall. Wavenumber 1 rainfall asymmetry presents the downshear-left maxima in the deep-layer vertical wind shear between 200 and 850 hPa for all the six basins prior to making a landfall. In general, wavenumber 1 rainfall tends to decrease less if there is an interaction between TCs and upper-level troughs located at the upstream of TCs over land. The maximum TC rain rate distributions tend to be located at the downshear-left (downshear) quadrant under the high (low)-potential vorticity conditions.

Spatiotemporal Analysis of Tropical Cyclone Landfalls in Northern Bay of Bengal, India and Bangladesh

In the Northern Bay of Bengal (NBoB), cyclonic storms (wind speed: ≥34 knots) inflict considerable losses in coastal Bangladesh and India. By building a georeferenced panel database of storm landfalls for this region, one can obtain spatial information on period-wise strike intensities. In this study, 168 cyclone strike locations along a 1259-km impact zone were analyzed for seven historical periods between 1877 and 2016. Cyclone landfall trends for this region denote a gradual reduction in storm frequencies since peaking in 1961–1980, which is generally in line with already established trends for the Northern Indian Ocean and Bay of Bengal basins. One notable exception for the NBoB in this is the unimodal seasonality of storm landfalls during 1877–1960, but that also conformed to the bimodal regional trends in the later periods. Over time, the median location of storm strikes in the NBoB has shifted eastward into westernmost Bangladesh, with a particularly marked variability in location after 1960. Northern Odisha and West Bengal, India, experienced more cyclone strikes over the past 140 years; but the highest mean wind speeds occurred along Bangladesh’s eastern coast. Also, storm impacts have varied considerably within and across zones; northern Odisha and the Sundarban region of West Bengal have withstood the greatest impacts. The pronounced spatial and temporal variations in cyclone impacts evinced in this study can provide valuable information for relief prioritization and community adaptation to cyclones in the region. The general method developed for this analysis can be applied to other coastal locations for management of storm impacts.

Future Changes in the Frequency and Destructiveness of Landfalling Tropical Cyclones Over East Asia Projected by High‐Resolution AGCMs

AbstractFuture changes in the frequency and destructiveness of landfalling tropical cyclones (TCs) over East Asia were investigated by analyzing the simulations of two high‐resolution (20–25‐km) atmospheric general circulation models forced by sea surface temperature (SST) in the present period (1979–2003) and under future warming conditions (2075–2099) of the RCP8.5 scenario. The present‐day simulations capture well the genesis count, tracks, and intensity associated with TCs striking the coastal areas of Taiwan‐East China (TWCN), the South China Sea‐Indochina (SCS) and the vicinity of Japan (JP). The frequency of landfalling TCs over TWCN, SCS, and JP is projected to nearly half by the end of the 21st century. However, these landfalling TCs induce enhanced destructive threats of stronger winds and heavier precipitation under the future warmer climate. Through attribution analysis we found the reduced frequency of landfalling TCs to be mainly caused by a decline in TC genesis count (rather than TC track changes), while the increased intensity of landfalling TCs is linked with changes in the TC intensification rate (as opposed to duration changes). Diagnoses of the genesis potential index and eddy energetics further suggest that the mid‐tropospheric drying and weakened synoptic‐scale eddy activity resulting from anticyclonic and downward circulations over the main TC genesis region create an unfavorable environment for TC genesis. In contrast, warmer SST, reduced vertical wind shear and enhanced efficiency of eddy kinetic energy generations appear over the regions before TC landfall, resulting in a more rapid intensification of TCs that later approach the coastal areas.

Tropical cyclones over the western north Pacific since the mid-nineteenth century

Tropical cyclone (TC) activities over the western North Pacific (WNP) and TC landfall in Japan are investigated by collecting historical TC track data and meteorological observation data starting from the mid-nineteenth century. Historical TC track data and TC best track data are merged over the WNP from 1884 to 2018. The quality of historical TC data is not sufficient to count the TC numbers over the WNP due to the lack of spatial coverage and different TC criteria before the 1950s. We focus on TC landfall in Japan using a combination of TC track data and meteorological data observed at weather stations and lighthouses from 1877 to 2019. A unified TC definition is applied to obtain equivalent quality during the whole analysis period. We identify lower annual TC landfall numbers during the 1970s to the 2000s and find other periods have more TC landfall numbers including the nineteenth century. No trend in TC landfall number is detected. TC intensity is estimated by an annual power dissipation index (APDI). High APDI periods are found to be around 1900, in the 1910s, from the 1930s to 1960s, and after the 1990s. When we focus on the period from 1977 to 2019, a significant increasing trend of ADPI is seen, and significant northeastward shift of TC landfall location is detected. On the other hand, TC landfall location shifts northeastward and then southwestward in about 100-year interval. European and US ships sailed through East and Southeast Asian waters before the weather station network was established in the late nineteenth century. Then, we focus on TC events in July 1853 observed by the US Naval Japan Expedition of Perry’s fleet and August 1863 by a UK Navy ship that participated in two wars in Japan. A TC moved slowly westward over the East China Sea south of the Okinawa Islands from 21 to 25 July 1853. Another TC was detected in the East China Sea on 15–16 August 1863 during the bombardment of Kagoshima in southern Japan. Pressure data are evaluated by comparing the observations made by 10 naval ships in Yokohama, central Japan during 1863–1864. The deviation of each ship pressure data from the 10 ships mean is about 2.7–2.8 hPa.

Markov Chain Monte Carlo simulation and regression approach guided by El Niño–Southern Oscillation to model the tropical cyclone occurrence over the Bay of Bengal

Tropical cyclone (TC) is one of the most devastating weather systems that causes enormous loss of life and property in the coastal regions of Bay of Bengal (BoB). Statistical forecasting of TC occurrence can help decision-makers and inhabitants in shoreline zones to take necessary planning and actions in advance. In this study, we have investigated the impact of El Nino–Southern Oscillation (ENSO) on the frequency of TC over the BoB by using 100 years TC and Southern Oscillation Index data. The frequency of TC is approximated through observation and Markov Chain Monte Carlo (MCMC) simulation. Two-sample Student’s t test has been applied for examining the statistical significance where the results are significant at 5% level for all cyclonic disturbances. The monthly and seasonal distribution show this feature more distinctly. The total annual frequency of depressions and cyclonic storms in El Nino and La Nina conditions does not differ much, but the monthly/seasonal distribution shows high differences for certain months and seasons. The simulated frequency of TC landfall using MCMC matches well with the observation. The proposed methodology is illustrated through a case study in BoB rim countries-Bangladesh, India, Sri Lanka and Myanmar. Poisson and Bayesian regression have also been used to predict the probabilities of TC frequency over the BoB. Both the regression approaches show 10 and 32% improvement than climatology for the forecast and cross-validation skill respectively. We have also analyzed TC impact over Bangladesh as a case study. Possible links of the variation of TC activities with the largescale geographical distribution of sea surface temperature, vertical wind shear, vorticity, moisture and relative humidity are also explored.

On the Improvement of the DSAEF_LTP Model to Heavy Precipitation Simulation of Landfalling Tropical Cyclones over China in 2018

In this study, the Dynamical-Statistical-Analog Ensemble Forecast model(DSAEF_LTP model) for landfalling tropical cyclone(LTC) precipitation was employed to simulate the precipitation of 10 LTCs that occurred over China in 2018. With similarity region scheme(SRS) parameter values added and TC intensity introduced to the generalized initial value(GIV), four groups of precipitation simulation experiments were designed to verify the forecasting ability of the improved model for more TC samples. Results show that the simulation ability of the DSAEF_LTP model can be optimized regardless of whether adding SRS values only, or introducing TC intensity into GIV, while the experiment with both the two improvements shows a more prominent advantage in simulating the heavier precipitation of LTCs. Compared with four NWP models(i.e., ECMWF, GFS, GRAPES and SMS-WARMS), the overall forecasting performance of the DSAEF_LTP model achieves a better result in simulating precipitation at the thresholds over 250 mm and performs slightly better than NWP models at the thresholds over 100 mm.