The Niño-3.4 index is a primary predictor of tropical cyclone (TC) rapid intensification (RI) in seasonal prediction, but fails to fully capture the evolution characteristics of El Niño–Southern Oscillation (ENSO) events. To address this limitation, a new metric—the ENSO decaying rate—is introduced in this study, which quantifies ENSO decaying flavors. When combined with the conventional Niño-3.4 index, the ENSO decaying rate improves the predictability of boreal autumn TC RI mean occurrence position on interannual timescales. This improvement arises because the ENSO decaying rate better captures the evolution of large-scale oceanic and atmospheric conditions that subsequently influence RI occurrence in boreal autumn. Furthermore, during the short-decaying El Niño transition years, the TC heat potential favors RI of autumn TCs in the South China Sea and the Philippine Sea. The ENSO decaying rate, rather than the conventional Niño-3.4 index, captures the TC heat potential conditions. Our findings demonstrate a strong association between the ENSO decaying rate and subsequent RI mean occurrence longitude in autumn on interannual timescales. This offers a potential pathway for improving the RI seasonal prediction skill.

Tropical cyclone (TC) activity over the western North Pacific (WNP) during the developing and persisting periods of multiyear La Ni & ntilde;a events exhibits distinct spatial patterns, particularly during boreal summer. In multiyear La Ni & ntilde;a's developing summers, TC activity is suppressed basinwide due to an anomalous anticyclonic circulation over the WNP. This circulation arises from the synergistic effects of the Indo-Pacific Ocean Capacitor effect following the preceding El Ni & ntilde;o and strengthened tropical easterlies driven by concurrently developing La Ni & ntilde;a. In contrast, during multiyear La Ni & ntilde;a's persisting summers, TC activity markedly increases over the northwestern WNP and adjacent coastal regions of the northwestern WNP. This arises from enhanced convection over the western WNP induced and maintained by long-lasting La Ni & ntilde;a, which, in summer, generates Rossby wave trains that induce an anomalous cyclone over the northwestern WNP and an anticyclone east of Japan. These systems provide favorable environments for TC activity over the northwestern WNP and amplify TC risks in coastal regions of the northwestern WNP. The differences in summer TC activity arise from the synergistic effects of different preceding El Ni & ntilde;o-Southern Oscillation (ENSO) conditions and the concurrent La Ni & ntilde;a. In addition, TC activity is relatively similar in subsequent autumns, which may be due to the dominant modulation of the current La Ni & ntilde;a. Our findings provide a more detailed picture beyond canonical views of ENSO-TC relationships from the perspective of multiyear La Ni & ntilde;a events, which could advance our physical understanding of TC activity and help TC seasonal prediction.

Tropical cyclone-induced storm surges pose significant and growing threats to coastal regions; however, their long-term evolution in response to changing tropical cyclone characteristics remains poorly quantified. Here, by conducting a comprehensive global analysis, we find that tropical cyclone-induced storm surge has increased globally by 20% over the period 1982-2024, which is also statistically significant in both hemispheres. Notably, such increases are 28% over the western North Pacific, 38.2% over the eastern Pacific and 31% over the South Pacific, respectively. Through statistical decomposition, we identify the poleward migration of tropical cyclone activity as a key factor amplifying the storm surge in both hemispheres. Furthermore, the intensification of major tropical cyclones and increasing sizes of weak tropical cyclones also play important roles in enhancing storm surges across multiple basins. These changes in tropical cyclone activity, particularly the poleward migration, are largely related to human-induced global warming, underscoring the intrinsic link between tropical cyclone characteristics and associated surge risk under a changing climate. Our findings highlight the necessity of explicitly incorporating the evolving tropical cyclone activity into climate projections and provide a critical framework for assessing compound coastal flood risks in a warming world.

The year 2025 is the third warmest year on record. Accompanying the exceptional heat, weather and climate extremes continued to swipe across the globe, with unprecedented magnitudes in many cases. The global monsoon regions were severely affected and hit with massive social and economic disruption, due to the combination of hazards and high exposure and vulnerability. This paper provides an overview of the extreme events that struck global monsoon regions in 2025, including their characteristics, extremity, and the resulting impacts, e.g., the spatially compound extreme rainfall–heatwaves throughout summer and autumn in East Asia, the extremely wet monsoon in South Asia, devastating tropical cyclones in various monsoon regions, etc. Brief physical background, especially the connections with monsoon activities, is also provided for understanding these extreme events. This provides insights into scientific challenges that remain to be addressed to improve our understanding for extreme events in monsoon regions.

Abstract The ocean serves as the energy source for tropical cyclones (TCs), and a TC typically encounters multiple oceanic warm and cold events during its lifecycle. While most existing studies emphasize individual thermal events, the net contribution of multiple warm and cold events to TC intensity remains unclear. We use a set of idealized coupled atmosphere–ocean simulations to examine how multiple ocean warm and cold thermal events affect TC intensity evolution throughout its lifecycle. Based on observational evidence, our experimental design includes one control experiment and 30 sensitivity experiments across three core scenarios (warm-anomaly dominated, cold-anomaly dominated, and warm-cold balanced anomalies). Relative to the control experiment, warm dominated experiments produce a stronger intensity evolution, cold dominated experiments produce a weaker decay, and the balanced experiments also lead to a slight increase. This response is fundamentally asymmetric, as the intensifying influence of warm events outweighs the weakening influence exerted by cold events with comparable magnitude. Moreover, this asymmetry increases with the magnitude of the oceanic thermal anomalies, and when the warm-anomaly amplitude is doubled, the simulated TC satisfies the rapid intensification criterion. These findings quantify the asymmetric forcing of ocean thermal structures on TCs, providing a crucial mechanistic basis for improving TC intensity forecasts.

Abstract The El Niño–Southern Oscillation (ENSO) is important to the interannual variability of tropical cyclone (TC) genesis in the Western North Pacific (WNP). However, the mechanisms for the TC seasonal changes in ENSO developing phase remain unclear. This study addresses the critical influences of the background sea surface temperature (SST) annual cycle and ENSO related sea surface temperature anomalies (SSTA) in regulating TC genesis seasonal changes. The results show that during eastern Pacific (EP) El Niño years, TC genesis increases in the southeastern WNP and decreases in the northwest in summer, while in autumn, TC genesis strengthens in the east and weakens in the west. For central Pacific (CP) El Niño events, basin-wide enhancement occurs in summer, with a southeast–northwest contrast in fall, whereas La Niña developing years exhibit nearly opposite patterns. These variations arise from anomalous convection generated by the combination of warm background SST annual cycle and ENSO SSTA, which modify large-scale conditions for TC genesis. Background SST can also strengthen ENSO evolution via the Bjerknes feedback, amplifying circulation impacts. This work provides a new perspective on the critical role of background SST annual cycle in shaping the ENSO–TC relationship, which is potentially helpful for improving seasonal TC prediction over the WNP.

The El Niño-Southern Oscillation (ENSO) has a significant impact on subsequent East Asian summer rainfall (EASR), and their relationship is unstable in observation. In this study, we utilize 10 models from the Paleoclimate Modeling Intercomparison Project Phases 3 and 4 to investigate the variability of the relationship between ENSO and EASR over the last millennium. All models reproduce the observed positive correlation between ENSO and EASR in the historical simulation, with the PMIP4 models outperforming the PMIP3 ones. In the last millennium simulation, the simulated spatial patterns of the ENSO-EASR correlation are similar to those in the historical simulation, and this relationship exhibits interdecadal variation closely related to ENSO variability. All models show the response of the EASR and Niño 3 index to volcanic activity over the last millennium. Still, external forcing is not the main driver for their low-frequency variability. The effects of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) on the ENSO-EASR relationship are further examined, and the negative phase of the PDO strengthens the ENSO-EASR relationship by enhancing the western Pacific subtropical high and the ENSO amplitude, while AMO shows little influence on the ENSO-EASR relationship.

Utilizing a data set of objectively estimated tropical cyclone (TC) size based on deep learning algorithms, this study investigates the relationship between the interannual variation of TC outer size over the western North Pacific and El Ni & ntilde;o-Southern Oscillation (ENSO) during July-September from 1981 to 2017. The size of TCs is measured by the mean radius of gale-force winds at their lifetime maximum intensity. Our results reveal an abrupt decadal change in the ENSO-TC size relationship: the annual mean TC size exhibited a strong correlation with the Ni & ntilde;o 3.4 SST index before 1998, but this correlation has significantly weakened since then. This change is primarily attributed to the more uniform distributions of cyclone expansion rate (CER) across ENSO phases during the past two decades. Climatically, environmental conditions favorable for TC size expansion weaken with increasing latitude, resulting in a dominant meridional gradient of CER. Before 1998, TC activity displayed a pronounced north-south contrast between El Ni & ntilde;o and La Ni & ntilde;a years, leading to a significantly higher mean CER for TCs during El Ni & ntilde;o episodes. In recent decades, however, interannual variations in TC genesis density have shifted to a southeast-northwest dipole pattern. This shift, along with changes in TC tracks, has substantially increased the latitudinal overlap of TC occurrences between warm and cold phases, thereby narrowing differences in CER distributions. Concurrently, changes in environmental conditions have become more favorable for TC size expansion during La Ni & ntilde;a years, further reducing disparities in TC size distributions across ENSO phases.

Tropical cyclone (TC) translation speed (TCTS) has been reported to significantly decrease during the past several decades over the western North Pacific (WNP). In this paper, we used an objective clustering method to categorize the WNP TCs into 7 typical tracks. A statistical method was utilized to quantitatively analyze the contribution by the changes in the TCTS and the relative track density of each category to the basin-mean TCTS trend. The decreasing trends of TCTS generated in the vicinity of the Philippines west of around 135°E and then entered the South China Sea (TCs in cluster 3), TCs formed in the east of the Philippine Sea (TCs in clusters 4), long-lifetime TCs (TCs in cluster 5) and recurving TCs formed closer to East Asia (TCs in cluster 6) contribute − 0.36 km h−1 decade−1 (69.94

Abstract Obvious biases in simulating tropical cyclone (TC) genesis of the current climate models hamper our understanding of TC changes. In this study, we found a delay of the seasonal cycle of TC genesis frequency over the western North Pacific (WNP) in most Coupled Model Intercomparison Project Phase 6 models. During the active TC season, the simulated south‐warming and north‐cooling surface temperature bias amplifies the meridional gradient and excites thermal winds. This weakens the western North Pacific Subtropical High and easterly monsoon trough, which further reduces TC genesis frequency over the western WNP in summer. But in autumn, positive TC genesis biases were only observed in coupled models over the eastern WNP. Both seasons contribute to the delayed seasonal cycle of TC frequency in models. Our findings highlight the importance of accurate simulation of surface temperature by climate models to TC simulations and aid in future model improvements.

Current coupled climate models contain large biases in simulating tropical cyclogenesis, reducing the confi-dence in tropical cyclone (TC) projection. In this study, we investigated the influence of sea surface temperature (SST) biases on TC genesis in the Coupled Model Intercomparison Project phase 6 simulations from 1979 to 2014. Positive TC genesis biases were found over the tropical central North Pacific (CNP) in most of climate models, including the high-resolution mod-els. Compared to coupled models, TC genesis density (TCGD) simulations over CNP in uncoupled models forced by observa-tional SST improved obviously. A warm SST bias over the tropical CNP in the coupled models is the main cause of TC genesis biases. The SST bias-induced diabatic heating leads to an anomalous Gill-type atmospheric circulation response, which con-tributes to a series of favorable environmental conditions for TC formation over the CNP. Numerical experiments were also performed with HiRAM to demonstrate the influence of SST biases on the TCGD simulation, further confirming our conclu-sion. The current results highlight the importance of improving TC simulation in state-of-the-art climate models by reducing SST simulation bias.

Global tropical cyclone (TC) genesis frequency (TCGF) has been documented to decrease or increase linearly in a changing climate. However, our numerical experiments show that the global TCGF exhibits a parabolic relation with spatio-uniform climate changes in sea surface temperature (SST) from -15 K to 5 K relative to the present climate, with the peak in the 5 K-cooler climate. The parabolic relation is found in all TC basins except the eastern North Pacific where TCGF keeps increasing with the changing climate. TCGF can be expressed as the product of the frequency of TC seeds and the TC survival rate (SR). Further analysis shows that this parabolic structure in the global TCGF depends on TC seeds rather than the TC SR. The TC SR exhibits an increasing trend with the SST increase, while TC seeds show a consistent change with TCGF, which might be linked to the changes in low-level relative humidity.

Storm surges are among the deadliest natural hazards, but understanding and prediction of year-to-year variability of storm surges is challenging. Here, we demonstrate that the interannual variability of observed storm surge levels can be explained and further predicted, through a process-based study in Hong Kong. We find that El Niño-Southern Oscillation (ENSO) exerts a compound impact on storm surge levels through modulating tropical cyclones (TCs) and other forcing factors. The occurrence frequencies of local and remote TCs are responsible for the remaining variability in storm surge levels after removing the ENSO effect. Finally, we show that a statistical prediction model formed by ENSO and TC indices has good skill for prediction of extreme storm surge levels. The analysis approach can be applied to other coastal regions where tropical storms and the climate variability are main contributors to storm surges. Our study gives new insight into identifying ‘windows of opportunity’ for successful prediction of storm surges on long-range timescales.

The El Niño-Southern Oscillation (ENSO) is crucial to the interannual variability of tropical cyclone (TC) genesis over the western North Pacific (WNP). However, most state-of-the-art climate models exhibit a consistent pattern of uncertainty in the simulated TC genesis frequency (TCGF) over the WNP in ENSO phases. Here, we analyze large ensemble simulations of TC-resolved climate models to identify the source of this uncertainty. Results show that large uncertainty appears in the South China Sea and east of the Philippines, primarily arising from two distinct atmospheric modes: the Matsuno-Gill-mode (MG-mode) and the Pacific-Japan-like pattern (PJ-mode). These two modes are closely associated with anomalous diabatic heating linked to tropical precipitation bias in model simulations. By conditionally constraining either of the modes, we can significantly reduce model uncertainty in simulating the dipole structure of the TCGF anomalies, confirming that it is the atmospheric circulation bias in response to tropical precipitation bias that causes uncertainty in the simulated WNP TCGF.

Tropical cyclone (TC) translation speed (TCS) over the western North Pacific (WNP) has experienced a long-term decreasing trend. To date, however, little is known about the multidecadal variability of TCS and its possible in-fluence on this trend. This study investigated the multidecadal variability of the WNP TCS and the underlying physical mechanisms. Results show that the WNP TCS presents robust multidecadal variability during the past seven decades, which is dominated by the TCS over the extratropics. Further analysis shows that the Atlantic multidecadal oscillation (AMO) is responsible for the TCS multidecadal variability. AMO positive (negative) phases lead to favorable (unfavor-able) large-scale environmental conditions for maintaining TCs over the extratropics, which results in longer (shorter) resi-dence time for TCs having been accelerated by the midlatitude westerlies, thus, leading to higher (lower) TCS. The TCS phase shift strongly offsets its slowdown trend, leading to the inconsistent trends during past decades. This inconsistency may also relate to the influence of extratropical transitioned cyclones without being totally excluded. These cyclones may be inhomogeneously recorded due to the absence of satellite observation before the 1980s. Our results indicate that inter-nal variation such as AMO may dominate TCS low-frequency variations over the past several decades. Previous studies have attributed the inconsistent trends of TCS during different subperiods to data inhomogeneity. This study shows that AMO can modulate the TCS trends in different subperiods with phase shift, thus providing new evidence for the recent controversial TCS slowdown.

The multi-year simulation of tropical cyclones (TCs) over the Western North Pacific (WNP) in the variable resolution (VR) CAM-MPAS model is studied. Experiments with the global quasi-uniform low resolution of 120 km (MPAS-UR) and the variable resolution mesh of 30–120 km refined over East Asia (MPAS-VR) are integrated from 1980 to 2005 following the Atmospheric Model Intercomparison Project protocol. By utilizing an objective detection method, TCs in ERA5 reanalysis and model simulations are tracked and compared against observations. MPAS-VR shows significant advantages over MPAS-UR as indicated by more realistic TC counts, intensities, lifetime distribution, and seasonal variation. The large-scale circulation and precipitation patterns associated with TCs are also improved in MPAS-VR relative to MPAS-UR. Based on the theory of Dynamic Genesis Potential Index, the multi-year TC records are further used to quantify the dependence of TC genesis on various dynamical environmental factors from the perspective of seasonal variation. We find that in ERA5, the relative contribution of the 500 hPa vertical pressure velocity term to TC genesis exceeds that of the 200–850 hPa vertical wind shear term, which is responsible for the August peak and strong seasonal variation of TC genesis. MPAS-UR fails to capture such relationship while MPAS-VR performs much better in this regard, suggesting that the higher skills in simulating the relative contributions from different dynamical environmental factors to the simulated seasonal cycle of TC genesis may explain the improvements from MPAS-UR to MPAS-VR.

Tropical cyclone (TC) lifetime maximum intensity (LMI) positions have been reported to migrate poleward globally during the last several decades. However, during the TC peak season, the trend of TC LMI position over the western North Pacific (WNP) is not as robust as that of genesis position. In this study, we found that the TC track change plays important roles in decreasing the genesis‐to‐LMI latitude distance (G2LD), which therefore leads to the inconsistent long‐term trends of genesis and LMI positions. A statistical approach was applied to quantitatively estimate the contributions by TC track change to the G2LD trend. The results show that the increase of near‐land formed short‐track TCs and the decrease of northwestward moving and eastward posited recurving TCs combined to make the largest contribution to the decreasing trend of the G2LD and thus to the insignificant long‐term trend of LMI position during peak season. Such TC track changes are closely related to the La Niña‐like warming pattern over the Pacific. The northeastward retreatment of the western Pacific subtropical high also plays an important role in reducing the northwestward moving TCs and increasing the recurving TCs over the northwestern WNP. Applying the same statistical approach to TC genesis positions indicates that the decrease of low‐latitude formed TCs makes the largest contribution to the poleward migration of genesis position, and the increase of high‐latitude formed TCs takes the second place. These low‐latitude formed TCs are mainly featured by northwestward moving and recurving tracks.

Predicting the peak‐season (July–September) tropical cyclones (TCs) in Southeast Asia (SEA) several months ahead remains challenging, related to limited understanding and prediction of the dynamics affecting the variability of SEA TC activity. Here, we introduce a new statistical approach to sequentially identify mutually independent predictors for the occurrence frequency of peak‐season TCs in the South China Sea (SCS) and east of the Philippines (PHL). These predictors, which are identified from the preseason (April‐June) environmental fields, can capture the interannual variability of different clusters of peak‐season TCs, through a cross‐season effect on large‐scale environment that governs TC genesis and track. The physically oriented approach provides a skillful seasonal prediction in the 41‐year period (1979–2019), with r = 0.73 and 0.54 for SCS and PHL TC frequency, respectively. The lower performance for PHL TCs is likely related to the nonstationarity of the cross‐season TC‐environment relationship. We further develop the statistical approach to a hybrid method using the predictors derived from dynamical seasonal forecasts. The hybrid prediction shows a significant skill for both SCS and PHL TCs, for lead times up to four or 5 months ahead, related to the good performance of models for the sea surface temperatures and low‐level winds in the tropics. The statistical and hybrid predictions outperform the dynamical predictions, showing the potential for operational use.

EDITORIAL article Front. Phys., 10 November 2022Sec. Interdisciplinary Physics Volume 10 - 2022 | https://doi.org/10.3389/fphy.2022.1041941

Tropical cyclone (TC) rainfall (TCR) over the western North Pacific (WNP) in TC peak season shows diverse responses to different El Niño flavors. Accumulated TCR increases over the low latitude regions (northwestern quadrant) of the WNP in eastern Pacific (central Pacific) El Niño but decreases over the entire basin in La Niña years. TCR hours are the primary causes of the variations in accumulated rainfall, while TCR rate takes second place. TCR hours are closely related to the total duration of TCs, which can be attributed to the slower translation speed and the longer TC travelling distance in eastern Pacific El Niño, but the increased (decreased) TC number for central Pacific El Niño (La Niña). Meanwhile, the TCR rate is closely related to TC intensity and 850 hPa vorticity. In eastern Pacific El Niño years, the decrease in steering flow and the southeastward displacement of TC genesis locations cause the changes in translation speed and travelling distance over the WNP, and the increased TC intensity over the offshore regions of eastern China. In central Pacific El Niño years, the easterly anomaly of midlatitude steering flow causes the increased TC number entering the corresponding region, and the increase of 850 hPa vorticity over the WNP basin leads to the enhanced TC intensity. In La Niña years, the combined effects of decreased 850 hPa vorticity and enhanced vertical wind shear over the Philippine Sea can result in the suppressed TC number and TC intensity.