Tropical Cyclone Best-track Research Articles

Revealing the intricate relationship: Droughts and typhoons in Taiwan using the Standardized Precipitation Index (SPI)

Study regionTaiwan Study focusThis study examines the relationship between typhoon parameters and droughts in Taiwan, particularly following the severe drought of 2020–2021. Using tropical cyclone best-track and satellite-based precipitation datasets from 1981 to 2020, we analyzed anomalies, correlation matrices, and wavelet coherence. Seasonal variations and long-term trends were also detected. New hydrological insights for the regionWe found a positive correlation between typhoon characteristics (count, duration, length, wind speed) in Taiwan and drought occurrence and severity, especially over 2–4 year periods. Conversely, negative relationships were observed between typhoon duration and length in the Western North Pacific (WNP) and drought indices in Taiwan, influenced by large-scale atmospheric patterns. Typhoon duration and length in the WNP had a greater impact on Taiwan's drought than typhoon quantity, showing significant coherence with long-term drought over multi-year to decadal timescales. Seasonally, drought intensity peaked in central and southeastern Taiwan during late winter and early spring when typhoons were absent, in contrast to the rainy summer typhoon season. Spatially, increasing drought trends were identified in central and southern Taiwan, while northern regions exhibited decreasing dryness, potentially linked to the concentration of typhoon landing points in the north. This study underscores the complex relationships between drought severity in Taiwan and typhoon behavior in both the vicinity of Taiwan and the WNP.

Influence of convective parameterization on the simulation of tropical cyclones over the South West Indian Ocean: A case study of tropical cyclone Idai (2019)

Proper configuration of the physical parameterization scheme is important for accurate outcomes of mesoscale weather forecasting model. This study evaluates the performance of four distinct cumulus parameterization schemes: the Kain-Fritsch (KF), Grell 3D ensemble (GR3D), Modified Tiedtke (MTIEDKE) and Modified Kain-Fritsch (MKF) schemes, in simulating Tropical Cyclone (TC) Idai (2019) in the Southern Indian Ocean. Utilizing the Weather Research Forecasting (WRF) model and TC best-track and satellite precipitation datasets, the research assesses the models' efficacy in replicating Idai's observed track and intensity. Results indicate that the KF, MTIEDKE, and MKF schemes reasonably capture Idai's southwestward track, with MKF demonstrating superior accuracy in reproducing observed intensity evolution. Conversely, the GR3D simulation exhibits a northwestward deviation, leading to notable track and intensity errors. Further investigations suggest that the smaller track and intensity differences in the MKF simulation are linked to the more accurate simulation of rainfall in both the surrounding environment and the TC inner-core region. The two factors exert strong influences on the large-scale steering flow and TC secondary circulation, respectively. The findings underscore the importance of selecting appropriate convective parameterization schemes for precise tropical cyclone simulations in the Southern Indian Ocean. This research contributes valuable insights into the intricate interaction between convective processes and atmospheric dynamics, offering implications for enhancing tropical cyclone prediction models in the region.

Applicability Evaluation of the Global Synthetic Tropical Cyclone Hazard Dataset in Coastal China

A tropical cyclone dataset is an important data source for tropical cyclone disaster research, and the evaluation of its applicability is a necessary prerequisite. The Global Synthetic Tropical Cyclone Hazard (GSTCH) dataset is a dataset of global tropical cyclone activity for 10,000 years from 2018, and has become accepted as a major data source for the study of global tropical cyclone hazards. On the basis of the authoritative Tropical Cyclone Best Track (TCBT) dataset proposed by the China Meteorological Administration, this study evaluated the applicability of the GSTCH dataset in relation to two regions: the Northwest Pacific and China’s coastal provinces. For the Northwest Pacific, the results show no significant differences in the means and standard deviations of landfall wind speed, landfall pressure, and annual occurrence number between the two datasets at the 95% confidence level. They also show the cumulative distributions of central minimum pressure and central maximum wind speed along the track passed the Kolmogorov–Smirnov (K-S) test at the 95% confidence level, thereby verifying that the GSTCH dataset is consistent with the TCBT dataset at sea-area scale. For China’s coastal provinces, the results show that the means or standard deviations of tropical cyclone characteristics between the two datasets were not significantly different in provinces other than Guangdong and Hainan, and further analysis revealed that the cumulative distributions of the tropical cyclone characteristics in Guangdong and Hainan provinces passed the K-S test at the 95% confidence level, thereby verifying that the GSTCH dataset is consistent with the TCBT dataset at province scale. The applicability evaluation revealed that no significant differences exist between most of the tropical cyclone characteristics in the TCBT and GSTCH datasets, and that the GSTCH dataset is an available and reliable data source for tropical cyclone hazard studies in China’s coastal areas.

The effects of intraseasonal oscillations on landfalling tropical cyclones in the Philippines during the boreal summer

As a kind of weather phenomenon with destructive wind and heavy rainfall, tropical cyclones (TCs), especially the landing TCs, can cause severer economic damage and losses of life. Philippines is one of the countries mostly affected by Tropical cyclones (TCs). Based on the best-track TC data and global atmospheric and oceanic reanalysis data, the present paper investigates the isolated and combined effects of two intraseasonal oscillations, the Madden-Julian oscillation (MJO) and the quasi-biweekly oscillation (QBWO), on landfall of TCs in the Philippines during boreal summer (May-September) in 1979-2019. The results show that both the MJO and the QBWO can significantly affect the frequency, landfall intensity, location, and translation speed of TCs that make landfall in the Philippines. During the convective (non-convective) phases of the MJO and the QBWO, more (less) frequent and stronger (weaker) TCs make landfall in the Philippines. This is due to the increased (decreased) frequency of TCs formation in the NWP and environmental factors in the region east of the Philippines that are favorable (unfavorable) for the development of TCs. With the northward propagation of the convective signals of the MJO and QBWO, the Western Pacific Subtropical High (WPSH) shifts eastward, and the steering flow is unfavorable for westward movement of NWP TCs. This, in turn, causes a northward shift in the landfall locations and a decrease in the translation speed of TCs. These results are helpful for the prediction of the TCs affecting the Philippines.

Factors Controlling Tropical Cyclone Intensification Over the Marginal Seas of China

Tropical cyclone (TC) intensification over marginal seas, especially rapid intensification (RI), often poses great threat to lives and properties in coastal regions and is subject to large forecast errors. It is thus important to understand the characteristics of TC intensification and the involved key factors affecting TC intensification over marginal seas. In this study, the 6-hourly TC best-track data from Shanghai Typhoon Institute of China Meteorological Administration, ERA-Interim reanalysis data, and TRMM satellite rainfall products are used to analyze and compare the climatological characteristics and key factors of different intensification stratifications over the marginal seas of China (MSC) and the western North Pacific (WNP) during 1980–2018. The statistical results show that TC intensification over the MSC is more likely to occur when TCs experience relatively large intensities, weak vertical wind shear, small translation perpendicular to the coastline, relatively high fullness, strong upper-level divergence, low-level relative vorticity, and high inner-core precipitation rate. The box difference index method is used to quantify the relative contributions of these factors to TC RI. Results show that the initial (relative) intensity contributes the most to TC RI over both the MSC and the WNP. The inner-core precipitation rate and translation perpendicular to the coastline are of second importance to TC RI over the MSC, while both vertical wind shear and TC fullness are crucial to TC RI over the WNP. These findings may help understand TC activity over the MSC and provide a basis for improving intensity prediction of TCs in the MSC.

The Performance of Three Exponential Decay Models in Estimating Tropical Cyclone Intensity Change After Landfall Over China

In this study, the performance of three exponential decay models in estimating intensity change of tropical cyclones (TCs) after landfall over China is evaluated based on the best-track TC data during 1980–2018. Results indicate that the three models evaluated can reproduce the weakening trend of TCs after landfall, but two of them (M1 and M2) tend to overestimate TC intensity and one (M3) tends to overestimate TC intensity in the first 12 h and underestimate TC intensity afterwards. M2 has the best performance with the smallest errors among the three models within 24 h after landfall. M3 has better performance than M1 in the first 20 h after landfall, but its errors increase largely afterwards. M1 and M2 show systematic positive biases in the southeastern China likely due to the fact that they have not explicitly included any topographic effect. M3 has better performance in the southeastern China, where it was originally attempted, but shows negative biases in the eastern China. The relative contributions of different factors, including landfall intensity, translational speed, 850-hPa moist static energy, and topography, to model errors are examined based on classification analyses. Results indicate that the landfall intensity contributes about 18%, translational speed, moist static energy and topography contribute equally about 15% to the model errors. It is strongly suggested that the TC characteristics and the time-dependent decay constant determined by environmental conditions, topography and land cover properties, should be considered in a good exponential decay model of TC weakening after landfall.

Rapid Weakening of Tropical Cyclones in Monsoon Gyres Over the Western North Pacific: A Revisit

The low-level monsoon trough over the western North Pacific (WNP) can evolve into a large cyclonic circulation, which is often termed a monsoon gyre (MG). Previous studies have revealed that tropical cyclones (TCs) embedded in MGs can experience rapid weakening (RW) and such RW might be attributed to the convective activity in the southeastern quadrant of the MG, which could induce asymmetries in a TC’s inner core structure, while the environmental factors, including the sea surface temperature (SST) and vertical wind shear (VWS), were not primary contributors to RW events. In this study, the possible role of large-scale environmental factors in association with the RW of TCs in MGs over the WNP is revisited based on the best-track TC and global reanalysis data during 2000–2018. Results indicate that TCs tend to weaken rapidly when they are embedded in the eastern semicircle of a MG, with the extreme RW events often occurring in the southeastern quadrant of a MG. However, different from previous studies, results from this study demonstrated that lower SST and strong large-scale VWS in the eastern semicircle of a MG are two major environmental factors contributing to the RW of TCs in MGs over the WNP. The different findings in this study from those in previous studies could be partly due to the different methods used to obtain the MG circulations and partly due to the environmental factors being analyzed in different quadrants of MG in this study.

Atmospheric moisture shapes increasing tropical cyclone precipitation in southern China over the past four decades

Although slower translation speed can induce a larger amount of local rainfall for an individual tropical cyclone (TC), whether change in total TC precipitation (TCP) affecting China is related to TC translation speed in the satellite era remains unclear. Based on multiple TC best-track datasets and a reanalysis dataset, we find a significant increasing trend in total TCP over two regions of southern China during 1980–2018. This upward trend can be attributed to the enhancing atmospheric water vapor content and moisture transport over southern China, however, TC intensity, frequency, and translation speed have no contributions. Given the potential linkage between the increasing atmospheric water vapor content over southern China and the western Pacific warming under global warming, our results suggest a likely role of anthropogenic global warming in the increasing TCP over southern China during the past 4 decades.

Western North Pacific tropical cyclone track forecasts by a machine learning model

An ensemble machine learning model for tropical cyclone (TC) track forecasts over the Western North Pacific was developed and evaluated in this study. First, we investigated predictors including TC climatology and persistence factors which were extracted from TC best-track dataset and storm’s surrounding atmospheric conditions which were extracted from ERA-Interim reanalysis. Then, we built a Gradient Boosting Decision Tree (GBDT) nonlinear model for TC track forecasts, in which 30-year data was used. Finally, using tenfold cross-validation method, the GBDT model was compared with a frequently used technique: climatology and persistence (CLIPER) model. The experimental results show that the GBDT model performs well in three forecast times (24 h, 48 h, and 72 h) with relatively small forecast error of 138, 264, and 363.5 km, respectively. The model obtains excellent TC moving direction aspects. However, the model is still insufficient to produce aspects of storm acceleration and deceleration, with mean moving velocity sensitivities all less than 60%. Nevertheless, the model obtains much more robust and accurate TC tracks relative to CLIPER model, where the forecast skills are 17.5%, 26.3%, and 32.1% at three forecast times, respectively. The presented study demonstrates that the GBDT model could provide reliable evidence and guidance for operational TC track forecasts.

Increasing Historical Tropical Cyclone-Induced Extreme Wave Heights in the Northern East China Sea during 1979 to 2018

Tropical cyclone (TC)-induced wind waves are a major concern in coastal safety, therefore quantifying the long-term change in extreme TC waves is critical for the design of coastal infrastructures and for understanding variations in coastal morphology. In this study, a trend analysis is performed on the TC-induced extreme wave heights in the northern East China Sea using numerically simulated wave height data during the period of 1979 to 2018. The simulation was forced with historical TC winds constructed using a parametric TC wind model with satellite-observed TC best-track data as the input. The results show consistently increasing extreme wave heights throughout the study region, which are induced predominantly by the increasing TC intensity. The increase rates (0.01–0.08 m yr−1) are relatively large (small) in offshore (nearshore) waters and at relatively high (low) latitudes. The spatial variability of the wave height trend is highly sensitive to the type of TC track. An analytical model of extreme wave height trend is developed that can efficiently estimate the rate of change in the extreme wave heights using extreme wind speed information.

Different Climatological Characteristics, Inner-Core Structures, and Intensification Processes of Simulated Intense Tropical Cyclones between 20-km Global and 5-km Regional Models

Abstract Climatological characteristics of simulated intense tropical cyclones (TCs) in the western North Pacific were explored with a 20-km-mesh atmospheric general circulation model (AGCM20) and a 5-km-mesh regional atmospheric nonhydrostatic model (ANHM5). From the AGCM20 climate runs, 34 intense TCs with a minimum central pressure (MCP) less than or equal to 900 hPa were sampled. Downscaling experiments were conducted with the ANHM5 for each intense TC simulated by the AGCM20. Only 23 developed into TCs with MCP ≤ 900 hPa. Most of the best-track TCs with an MCP ≤ 900 hPa underwent rapid intensification (RI) and attained maximum intensities south of 25°N. The AGCM20 simulated a similar number of intense TCs as the best-track datasets. However, the intense AGCM20 TCs tended to intensify longer and more gradually; only half of them underwent RI. The prolonged gradual intensification resulted in significant northward shifts of the location of maximum intensity compared with the location derived from two best-track datasets. The inner-core structure of AGCM20 TCs exhibited weak and shallow eyewall updrafts with maxima below an altitude of 6 km, while downscaling experiments revealed that most of the intense ANHM5 TCs underwent RI with deep and intense eyewall updrafts and attained their maximum intensity at lower latitudes. The altitudes of updraft maxima simulated by the AGCM20 descended rapidly during the phase of greatest intensification as midlevel warming markedly developed. The change in major processes responsible for precipitation in AGCM20 TCs before and after maximum intensification suggests close relationships between the large-scale cloud scheme and midlevel warming and prolonged gradual intensification.

Contribution of Tropical Cyclones to Rainfall at the Global Scale

This study quantifies the relative contribution of tropical cyclones (TCs) to annual, seasonal, and extreme rainfall and examines the connection between El Niño–Southern Oscillation (ENSO) and the occurrence of extreme TC-induced rainfall across the globe. The authors use historical 6-h best-track TC datasets and daily precipitation data from 18 607 global rain gauges with at least 25 complete years of data between 1970 and 2014. The highest TC-induced rainfall totals occur in East Asia (>400 mm yr−1) and northeastern Australia (>200 mm yr−1), followed by the southeastern United States and along the coast of the Gulf of Mexico (100–150 mm yr−1). Fractionally, TCs account for 35%–50% of the mean annual rainfall in northwestern Australia, southeastern China, the northern Philippines, and Baja California, Mexico. Seasonally, between 40% and 50% of TC-induced rain is recorded along the western coast of Australia and in islands of the south Indian Ocean in the austral summer and in East Asia and Mexico in boreal summer and fall. In terms of extremes, using annual maximum and peak-over-threshold approaches, the highest proportions of TC-induced rainfall are found in East Asia, followed by Australia and North and Central America, with fractional contributions generally decreasing farther inland from the coast. The relationship between TC-induced extreme rainfall and ENSO reveals that TC-induced extreme rainfall tends to occur more frequently in Australia and along the U.S. East Coast during La Niña and in East Asia and the northwestern Pacific islands during El Niño.

The Relationship between Sea Surface Temperature and Maximum Intensification Rate of Tropical Cyclones in the North Atlantic

Abstract An empirical relationship between sea surface temperature (SST) and the maximum potential intensification rate (MPIR) of tropical cyclones (TCs) over the North Atlantic has been developed based on the best-track TC data and the observed SST during 1988–2014. Similar to the empirical relationship between SST and the maximum potential intensity of TCs previously documented, results from this study show a nonlinear increasing trend of the MPIR with increasing SST, with a more rapid increasing trend when SST is higher than 27°C. Further analyses indicate that about 28% of intensifying TCs over the North Atlantic reached 50% of their MPIR and only 7% reached 80% of their MPIR at the time when they were at their lifetime maximum intensification rates. Moreover, a TC tended to have a larger intensification rate when it was located in regions with higher SST and lower vertical wind shear (VWS). This indicates that although the MPIR–SST relationship is much stronger than that for the IR rate versus SST for most TCs, the actual intensification rate of a TC is determined by not only the SST but also other environmental effects, such as VWS. Additional results from a simplified dynamical system previously developed for TC intensity prediction suggest an SST-dependent TC MPIR, similar to that fitted from observations. However, the MPIR obtained from the observational fitting seems to underestimate the MPIR in regions with low SST at higher latitudes where VWS is often large. Nevertheless, this study provides the observational evidence for the existence of the MPIR for TCs.

Influence of Oceanic Intraseasonal Kelvin Waves on Eastern Pacific Hurricane Activity

Abstract Recent studies have highlighted the role of subsurface ocean dynamics in modulating eastern Pacific (EPac) hurricane activity on interannual time scales. In particular, the well-known El Niño–Southern Oscillation (ENSO) recharge–discharge mechanism has been suggested to provide a good understanding of the year-to-year variability of hurricane activity in this region. This paper investigates the influence of equatorial subsurface subannual and intraseasonal oceanic variability on tropical cyclone (TC) activity in the EPac. That is to say, it examines previously unexplored time scales, shorter than interannual, in an attempt to explain the variability not related to ENSO. Using ocean reanalysis products and TC best-track archive, the role of subannual and intraseasonal equatorial Kelvin waves (EKW) in modulating hurricane intensity in the EPac is examined. It is shown first that these planetary waves have a clear control on the subannual and intraseasonal variability of thermocline depth in the EPac cyclone-active region. This is found to affect ocean subsurface temperature, which in turn fuels hurricane intensification with a marked seasonal-phase locking. This mechanism of TC fueling, which explains up to 30% of the variability of TC activity unrelated to ENSO (around 15%–20% of the total variability), is embedded in the large-scale equatorial dynamics and therefore offers some predictability with lead time up to 3–4 months at seasonal and subseasonal time scales.

An intercomparison of tropical cyclone best-track products for the southwest Pacific

Abstract. Recent efforts to understand tropical cyclone (TC) activity in the southwest Pacific (SWP) have led to the development of numerous TC databases. The methods used to compile each database vary and are based on data from different meteorological centres, standalone TC databases and archived synoptic charts. Therefore the aims of this study are to (i) provide a spatio-temporal comparison of three TC best-track (BT) databases and explore any differences between them (and any associated implications) and (ii) investigate whether there are any spatial, temporal or statistical differences between pre-satellite (1945–1969), post-satellite (1970–2011) and post-geostationary satellite (1982–2011) era TC data given the changing observational technologies with time. To achieve this, we compare three best-track TC databases for the SWP region (0–35° S, 135° E–120° W) from 1945 to 2011: the Joint Typhoon Warning Center (JTWC), the International Best Track Archive for Climate Stewardship (IBTrACS) and the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC). The results of this study suggest that SPEArTC is the most complete repository of TCs for the SWP region. In particular, we show that the SPEArTC database includes a number of additional TCs, not included in either the JTWC or IBTrACS database. These SPEArTC events do occur under environmental conditions conducive to tropical cyclogenesis (TC genesis), including anomalously negative 700 hPa vorticity (VORT), anomalously negative vertical shear of zonal winds (VSZW), anomalously negative 700 hPa geopotential height (GPH), cyclonic (absolute) 700 hPa winds and low values of absolute vertical wind shear (EVWS). Further, while changes in observational technologies from 1945 have undoubtedly improved our ability to detect and monitor TCs, we show that the number of TCs detected prior to the satellite era (1945–1969) are not statistically different to those in the post-satellite era (post-1970). Although data from pre-satellite and pre-geostationary satellite periods are currently inadequate for investigating TC intensity, this study suggests that SPEArTC data (from 1945) may be used to investigate long-term variability of TC counts and TC genesis locations.

Distribution characteristics of the intensity and extreme intensity of tropical cyclones influencing China

To address the deficiency of climatological research on tropical cyclones (TCs) influencing China, we analyze the distributions of TCs with different intensities in the region, based on the best-track TC data for 1949–2011 provided by the Shanghai Typhoon Institute. We also present the distributions of 50- and 100-yr return-period TCs with different intensities using the Gumbel probability distribution. The results show that TCs with different intensities exert distinctive effects on various regions of China and its surrounding waters. The extreme intensity distributions of TCs over these different regions also differ. Super and severe typhoons mainly influence Taiwan Island and coastal areas of Fujian and Zhejiang provinces, while typhoons and TCs with lower intensities influence South China most frequently. The probable maximum TC intensity (PMTI) with 50- and 100-yr return periods influencing Taiwan Island is below 890 hPa; the PMTI with a 50-yr return period influencing the coastal areas of Fujian and Zhejiang provinces is less than 910 hPa, and that with a 100-yr return period is less than 900 hPa; the PMTI with a 50-yr return period influencing the coastal areas of Hainan, Guangdong, and the northern part of the South China Sea is lower than 930 hPa, and that with a 100-yr return period is less than 920 hPa. The results provide a useful reference for the estimation of extreme TC intensities over different regions of China.

Estimating Tropical Cyclone Damages Under Climate Change in the Southern Hemisphere Using Reported Damages

This paper estimates the damages from tropical cyclones (TCs) in the Southern Hemisphere under future climate change scenarios based on the historical TC records in Australia. From the best-track TC data, we examine the changes in frequency, intensity, and economic damage of the TCs that made landfall since 1970. From the detailed individual TC reports, damage estimates are constructed based on reported damages. We find that the TC frequency has significantly declined over time. The intensity, however, does not show a significant trend. Average damage per TC has declined significantly from 43 million AUD in the 1970s to 11 million in the 1990s. This paper finds that 1 % decrease in minimum central pressure leads to 32.7 % increase in economic damage, which is more than three times larger than that found in the US hurricane study with regards to maximum wind speeds. For future damage projections, characteristics of the 14,000 TCs generated under seven different AOGCM climate models are applied. All seven climate models predict a decrease in TC frequency in the Southern Hemisphere but intensity predictions vary. By the end of the twenty second century, changes in climate are expected to increase the TC damage under the MRI (\(+\)94 %), the MIROC (\(+\)73 %), and the CSIRO (\(+\)66 %) model due to increased intensity. However, TC damage is expected to fall under the GFDL (\(-\)92 %) and the CNRM (\(-\)85 %) model due to decreased intensity and frequency. Adaptation will be a key determinant of the future vulnerability to TCs in the Southern Hemisphere.

Oscillation in frequency of tropical cyclones passing Taiwan and Hainan Islands and the relationship with summer monsoon

The temporal variations in the frequency of tropical cyclones (TCs) traversing the Taiwan and Hainan Islands (TH islands), were analyzed using a best-track TC dataset from the Joint Typhoon Warning Center for the period 1945–2007. Results show that the oscillations were interannual and interdecadal on the timescales of 2–8 and 8–12 years, respectively. It is also shown that the number of TCs formed in the western North Pacific basin (WNP) and of those traversing the TH islands varied intraseasonally. These results also held for typhoons traversing the TH islands, although the oscillations were less apparent. This study identified interrelationships between the frequency of TCs making landfall on the TH islands and the East Asia summer monsoon (EASM), the South Asia summer monsoon (SASM), and the South China Sea summer monsoon (SCSSM). The SCSSM significantly influenced the number of TCs traversing Hainan Island, but had little influence on the number of TCs traversing Taiwan Island. By contrast, the SASM influenced the numbers of TCs traversing both of the TH islands, shown by correlation coefficients of 0.41 for Taiwan Island and −0.25 for Hainan Island. In addition, the frequency of TC landfall on Taiwan Island increased during years of enhanced EASM, as indicated by a correlation coefficient of 0.4.

An Examination of Tropical Cyclone Position, Intensity, and Intensity Life Cycle within Atmospheric Reanalysis Datasets

Abstract The following study examines the position and intensity differences of tropical cyclones (TCs) among the Best-Track and five atmospheric reanalysis datasets to evaluate the degree to which reanalyses are appropriate for studying TCs. While significant differences are found in both reanalysis TC intensity and position, the representation of TC intensity within reanalyses is found to be most problematic owing to its underestimation beyond what can be attributed solely to the coarse grid resolution. Moreover, the mean life cycle of normalized TC intensity within reanalyses reveals an underestimation of both prepeak intensification rates as well as a delay in peak intensity relative to the Best-Track. These discrepancies between Best-Track and reanalysis TC intensity and position can further be described through correlations with such parameters as Best-Track TC age, Best-Track TC intensity, Best-Track TC location, and the extended Best-Track TC size. Specifically, TC position differences within the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), ECMWF Interim Re-Analysis (ERA-I), and Modern Era Retrospective-Analysis for Research and Applications (MERRA) exhibit statistically significant correlations (0.27 ≤ R ≤ 0.38) with the proximity of TCs to observation dense areas in the North Atlantic (NATL) and western North Pacific (WPAC). Reanalysis TC intensity is found to be most strongly correlated with Best-Track TC size (0.53 ≤ R ≤ 0.70 for maximum 10-m wind speed; −0.71 ≤ R ≤ −0.53 for minimum mean sea level pressure) while exhibiting smaller, yet significant, correlations with Best-Track TC age, Best-Track TC intensity, and Best-Track TC latitude. Of the three basins examined, the eastern North Pacific (EPAC) has the largest reanalysis TC position differences and weakest intensities possibly due to a relative dearth of observations, the strong nearby terrain gradient, and the movement of TCs away from the most observation dense portion of the basin over time. The smaller mean Best-Track size and shorter mean lifespan of Best-Track EPAC TCs may also yield weaker reanalysis TC intensities. Of the five reanalyses, the smaller position differences and stronger intensities found in the Climate Forecast System Reanalysis (CFSR) and Japanese 25-year Reanalysis (JRA-25) are attributed to the use of vortex relocation and TC wind profile retrievals, respectively. The discrepancies in TC position between the Best-Track and reanalyses combined with the muted magnitude of TC intensity and its partially nonphysical life cycle within reanalyses suggests that caution should be exercised when utilizing these datasets for studies that rely either on TC intensity (raw or normalized) or track. Finally, several cases of nonphysical TC structure also argue that further work is needed to improve TC representation while implying that studies focusing solely on TC intensity and track do not necessarily extend to other aspects of TC representation.

Quantifying the possible existence of undocumented Atlantic warm-core cyclones in NOAA/CIRES 20th Century Reanalysis data

[1] Prior to 1966, the lack of satellite imagery led to an unknown number of tropical cyclones (TCs) in the Atlantic Basin remaining undetected by traditional surface observational networks. Previous research has shown that this historical undersampling has led to difficulties in interpreting long-term trends in TC activity. In this study, advances in global reanalysis methods are used to further guide existing TC Best-Track revision efforts, specifically for the pre-satellite era. First, a series of atmospheric proxies of TC passage in the NOAA/CIRES 20th Century Reanalysis dataset are constructed for the satellite-era. Next, similar magnitude signatures (not corresponding to known Best-Track TCs) are identified in the pre-satellite era and subjected to further synoptic verification. Surface observations are used to categorize candidate events into three confidence bins. A small but significant number of the candidate events are cases that warrant further examination by ongoing reanalysis efforts. As this method shows promise for use in other TC basins around the world, preliminary results suggest that this technique may potentially lead to a more complete climatological record of global TC incidence and an improved understanding of long-term trends in activity.