This paper proposes a novel approach to identifying the annual cycle and variability of the East Asia and western Pacific (EA-WP) monsoon. A low-level circulation pattern (LCP) calendar is constructed based on nine LCPs obtained from K-means cluster analysis for 46 years (1979–2024) of daily 850-hPa wind data. The LCP daily occurrence frequency reveals climatological features of the monsoon annual cycle and seasonal progression. The LCP-based summer and winter monsoon indices well represent key monsoon characteristics. A strong East Asian summer monsoon (EASM) corresponds to more frequent occurrences of LCP featuring low-level anticyclonic circulation over the western North Pacific, while a strong East Asian winter monsoon (EAWM) corresponds to more frequent occurrences of LCPs characterized by low-level northerly winds over the South China Sea and the Philippine Sea. The variability of EASM and EAWM is synchronized during the developing phase of ENSO events. Strong (weak) EA-WP monsoon years are marked by strong (weak) EASM followed by strong (weak) EAWM, whereas no clear relationship is found between EASM and its preceding EAWM. Approximately 86

Convection over the South China Sea (SCS) exhibits distinct quasi-biweekly oscillations (QBWO). The QBWO_SCS modulates marine boundary layer jets (MBLJs) embedded in the southwesterly monsoon flow during June, the late Meiyu season. During the first half cycle from Phase 1 (P1) to Phase 2 (P2), convection is most suppressed over the SCS in P2, while enhanced convective activity is observed within the Meiyu trough over southeastern China. An anomalous low-level anticyclonic circulation over the SCS leads to increased (decreased) MBLJ frequency over the northern (southern) SCS, and these anomalies reverse in Phase 4 (P4). In P2, QBWO_SCS-intensified MBLJs near the southeastern coast of China create favorable conditions for heavy inland rainfall. First, strengthened southwesterly MBLJs enhance moisture transport from the SCS to inland southeast China and increase moisture convergence within the Meiyu trough. Second, warm, moist air advected inland meets continental cold air, enhancing baroclinicity and frontogenesis, which strongly correlates with inland rainfall maxima. Third, the topography of southeast China amplifies rainfall through orographic lifting as moisture-laden MBLJs impinge on elevated terrain. In contrast, during P4, weakened MBLJs reduce moisture transport, convergence, and frontogenesis, leading to diminished inland rainfall. Meanwhile, QBWO_SCS-induced convection-coupled circulation in P4 supports monsoon trough development and enhances heavy precipitation over coastal south China, the northern SCS, and southern Taiwan. About 25% of QBWOs over SCS are positively correlated with low-level cyclonic flow originating from QBWOs over the tropical western Pacific, 10% are weakly modulated by the boreal summer intraseasonal oscillation, and 65% are caused by other processes.

Monsoon onset marks an abrupt seasonal transition from a dry to a moist atmosphere, but physical processes associated with the monsoon onset over India and the Arabian Sea (AS) are not fully understood. In this study, a northward propagating convective phase of intraseasonal oscillations (ISOs), associated with low-level cyclonic circulation, is identified as a crucial factor in initiating the monsoon onset. The northward propagation is sustained by a positive moist static energy (MSE) tendency to the north and a simultaneous negative tendency to the south of the convective center. Results from the MSE budget diagnosis indicate that the MSE tendency dipole is attributed to horizontal moisture advection. Under a wetter (dryer) background environment over southeastern (northwestern) AS, the intraseasonal cyclonic circulation enhances (reduces) the MSE to its north (south). In addition, the northward propagation is controlled by a meridional asymmetry of background convective instability (BCI). During the pre-onset stage, the accumulation of background low-level moisture over the northern AS due to meridional moisture transport by cross-equatorial flow enhances local BCI. A more unstable background environment over the AS, compared to the equatorial western Indian Ocean (EWIO), facilitates the northward propagation of ISOs. ENSO exerts a marked impact on the monsoon onset through the modulation of the meridional asymmetry of BCI. During post-La Nina Springs, both the enhanced meridional SST gradient over EWIO and the stronger cross-equatorial low-level flow over the AS help trigger the northward-propagating ISOs and thus lead to an earlier monsoon onset.

East Asian monsoon shows strong annual cycle with the wet season in summer and dry in winter. In addition to annual cycle, some monsoon regions exhibit distinct climatological sub-seasonal variations such as fast annual cycle, climatological intraseasonal oscillations (CISOs) and climate singularities. In this paper a significant cyclic-type outgoing longwave radiation (OLR) singularity during the spring to summer transition period over the South China Sea (SCS) is identified based on the daily OLR data from 1979 to 2023. The quasi-CISO in each individual year is invented as an analogue to CISO. Its relationship with Madden–Julian Oscillation (MJO) and the SCS summer monsoon onset (SCSSM) is analyzed. The quasi-CISO shows large interannual variability. A group of years with the quasi-CISO amplitudes larger than the medium of all sample years are selected to form the quasi-CISO mode. Among them 72% of the quasi-CISO cyclic valley coincides with the SCSSM onset time represented by the persistent intensification of the monsoonal westerlies, which are the SCS-CISO years. The MJO activity during the sixteen SCS-CISO years shows three different levels. Composite results of eight SCS-CISO years with strong MJO show clear synchronized planetary- and regional-scale convection and circulation progressions where strong MJOs over the equatorial Indian Ocean appeared two weeks before SCSSM onset. Strong convection over the SCS associated with the SCSSM onset process can be triggered by the enhanced low-level southerly flow by MJO’s subsidence leg over the equatorial maritime continent through increasing the moisture transport. This study provides observational-based evidence that supports earlier findings about CISO, CMJO and SCSSM onset. The findings can be applied to evaluate the Sub-seasonal to Seasonal forecast model products for better understanding of the extended-range weather and climate predictability.

The first version of the Taiwan Central Weather Bureau one-tier (TCWB1T) fully coupled global atmospheric and oceanic modeling forecast system had been developed and implemented as a routine operation for seasonal prediction at Central Weather Bureau (CWB) in 2017, with a minor revision in 2020. Based on NCEP CFSv1, the global atmospheric model in NCEP CFSv1 was replaced by CWB’s atmospheric global spectral model (GSM) and coupled with the GFDL MOM3. Several parameters have been tested and tuned in the CWB atmospheric GSM, achieving an optimal configuration with better sea surface temperature (SST) predictions for integration more than one year. Using NCEP CFSR as the initial condition, TCWB1T conducted hindcasts from 1982 to 2011 and forecasts from 2012 to 2019 to analyze its performance. The results of these hindcasts and forecasts show that the TCWB1T can make useful predictions as verified against the observations of OISST, ERSST, CFSR, and GPCP based on the methods of EOF, RMSE, anomaly correlation, ranked probability skill score (RPSS), reliability diagram (RD), and relative operating characteristics (ROCs). TCWB1T also has the same level of skill scores as NCEP CFSv2 and/or the ECMWF fifth-generation seasonal forecast system (SEAS5), based on EOF, anomaly pattern correlation, climatological bias, RMSE, temporal correlation, and anomaly correlation percentage of forecast skill. TCWB1T shows forecast skill that is better in winter than in summer. Overall, it indicates that TCWB1T can be used for seasonal ENSO predictions.

Episodic cold surges in the East Asia winter monsoon can penetrate deep into the South China Sea (SCS), enhance consequent tropical rainfall, and further strengthen the East Asia meridional overturning circulation. These cold surges can promote strong surface fluxes and lead to a deeper marine boundary layer (MBL). However, there is a lack of boundary layer studies over the SCS, unlike many other well-studied regions such as the north Atlantic Ocean and the central-eastern Pacific Ocean. In this study, we use high resolution radiosonde data of temperature and humidity profiles over Dongsha Island (116.69E, 20.70N) to identify the inversion layer, mixed layer, cloud base, cloud top, and factors controlling low cloud cover for the period of December-January-February from 2010 to 2020. We perform an energy budget analysis with ERA-5 meteorological variables and surface fluxes. Here we show a strong turbulent flux convergence of both heat and moisture within the SCS MBL during cold surges, which leads to a lifting of the mixed layer to ~1.0 km and inversion layer to ~2.0 km and associated cloud development over Dongsha Island. The cold and dry horizontal advection is balanced by this vertical turbulent flux convergence in the energy budget. Overall, cold surges over the SCS enhance lower branch of winter monsoon meridional overturning circulation with stronger inversion and higher low cloud covers.

In boreal summer of 2022, Pakistan experienced extremely high rainfall, resulting in severe flooding and displacing over 30 million people. At the same time, heatwaves persisted over central China and Europe. The coexistence of these extreme events suggests a possible linkage. Our analysis indicated that the record rainfall was mainly induced by compounding factors. These included (1) La Niña-induced strong anomalous easterlies over the northern Indian subcontinent, (2) intense southerlies from the Arabian Sea with an upward trend in recent decades, (3) an interaction between extratropical and tropical systems, specifically the northerly flow downstream of the Europe blocking and the southerly monsoon flow from the Arabian Sea. Wave activity flux and regression analyses unveiled a distinct stationary Rossby wave-like pattern connecting the flooding in Pakistan and heatwaves in Europe and China. This pattern, an emerging teleconnection pattern in recent decade, exhibited substantial differences from the reported teleconnection patterns. We also noted the positive feedback of the excessive Pakistan rainfall could further enhance the large-scale background flow and the heavy rainfall itself. The 2022 Pakistan flood event was an intensified manifestation of the 2010 Pakistan flood event, which was also caused by compounding factors, but occurred in a more pronounced upward trend in the both tropics and extratropics.

During the first half month of April 2022, the Philippines experienced severe disasters associated with the weak but deadly tropical storm Megi that caused 214 deaths and two sunken ships. This prompted us to investigate the extended-range prediction skill of the springtime Philippine sub-seasonal scale rainfall extremes in the subseasonal-to-seasonal (S2S) prediction database. The results suggest that the S2S models can well predict the extremity of the 2022 springtime sub-seasonal peak rainfall event (SPRE) ten days ahead. In addition to the La Niña sea surface temperature anomalies, this prolonged rainfall event, from March 26 - April 14, 2022, was associated with an anomalous cyclonic circulation straddled over the South China Sea (SCS) and the Philippine Sea and persisted for two weeks. The strong relationship between the El Niño and Southern Oscillation (ENSO) and the springtime (February–April) rainfall variability in the Philippines is clearly revealed in the analysis of 25 years of observational and hindcast data. The extremely wet SPREs tend to occur during the La Niña springs, while the extremely dry SPREs tend to occur during the El Niño springs. The Madden-Julian oscillation (MJO) and equatorial Rossby (ER) waves that are capable of modulating the sub-seasonal rainfall extremes were weak when the deadly SPRE occurred in April 2022. Thus, the extended-range forecast skill of this example can be interpreted as the baseline skill of the current S2S prediction revealed in the multi-model database. The findings suggest that the SPRE is a useful item to be included in the operational forecast as potential opportunities to harness the benefits of S2S prediction and applications.

The decadal-scale variations of the Asian summer monsoon and the tropical cyclone (TC) activity over the western North Pacific (WNP) and the South China Sea (SCS) are of great scientific and societal importance. The period of 2010-2019 was identified as the most inactive decade since 1961 in terms of TC genesis over the SCS and the Philippine Sea during May (Cho et al. 2022). In this paper we extended the analysis by using 40-yr (1981-2020) data to illustrate the relationship between the SCS TC frequency in May and the spring-to-summer transition of Asian monsoon systems. The results show clear decadal-scale variations of TC frequency with two active decades during the 1980s and 2000s, and two inactive decades during the 1990s and 2010s. The circulation and surface air temperature contrast during the earlier two decades is drastically different from the contrast during later two decades. The difference can be understood as decadal-scale variations of two leading modes of the 40-yr March-June precipitation in Asian-Australian-Pacific monsoon region. For the earlier two decades, the contrast of active and inactive SCS TC frequency in May can be explained by the difference in EOF2. The positive EOF2 corresponds to a wet and dry dipole pattern of the concurrent anomalies with enhanced convection over the eastern Indian Ocean and suppressed convection over the western Pacific warm pool. For the later two decades, the contrast can be explained by the difference in EOF1, which shows a meridional dipole pattern over eastern Indian Ocean reflecting the northward movement of the ITCZ. Among four decades, the decade of 2001-2010 shows the earliest northward transition of the ITCZ and the most active SCS TC frequency in May. Although the decades of 1981-1990 and 1991-2000 show strong difference in TC frequency, no discernable difference in monsoon seasonal transition is detected.

An inter-decadal increase (1990–2009) in the western North Pacific (WNP) tropical cyclone (TC) genesis frequency in May has recently been reported. The TC decadal changes was attributed to an advanced monsoon onset over the Asian Summer Monsoon region, particularly over the South China Sea (SCS) in May. In the present study, we used 60 years (1961–2020) of TC data and 40 years (1981–2020) of the global reanalysis data to investigate the unique changes of the SCS TC activity during May and the associated large-scale environment. We find that the increasing trend was weakened during the most recent decade (2011–2020), and the advanced monsoon onset was not discernable. The period of 2011–2020 was identified as a decade of the minimum TC genesis frequency over the SCS in May since 1961. The extremely inactive TC genesis was attributed to the weak low-level cross equatorial monsoonal flow over the Indo-Pacific warm pool and the weak westerly monsoon (easterly anomalies) north of equator from the western Pacific through the Philippine Sea and the SCS to the Bay of Bengal. The weak tropical monsoon was associated with subtropical anticyclonic and suppressed convection north of the equator and the opposite wind and convection south of the equator. The anticyclonic circulation over the SCS was particularly strong that inhibited TC genesis during the first decade of the twenty-first century.

The South Asian High (SAH) is the most pronounced boreal summer upper tropospheric dynamic system over Asia. The dominant modes of the SAH sub-seasonal variability are captured by the EOFs of 200-hPa daily geopotential height over 40°-120°E, 10°-40°N from June to August during 1979-2021. EOF1 shows a single center pattern with the maximum variance over the Iranian Plateau. The corresponding principal component (PC) shows an increasing tendency of the SAH in particular after the year 2010. EOF2 shows an east-west dipole pattern. Its PC has a spectral peak period of around 20 days. The composite analysis based on the negative (west mode) and positive (east mode) phases of the EOF2 reveals that the wave trains associated with the west and east modes can be traced back to the northeastern Atlantic and Ural Mountains, respectively, about two weeks before the wave reached the SAH region. The Ural ridge for the east mode excited two branches of waves, one propagated equatorward into central Asia and another propagated along 60°N into Central Siberian Plateau. The two wave trains later formed a quadrupole pattern over and to the north of the SAH. The west (east) mode composite precipitation shows wet (dry) over the Indian subcontinent and dry (wet) over the Bay of Bengal over South Asia, while over East Asia it shows dry (wet) over North China and wet (dry) over South China. In addition, the east mode has an unique tripolar pattern with dry over East China and wet over Japan and the Philippines. The sub-seasonal relationship between high-latitude Rossby waves and the SAH can influence the monsoon precipitation that is tightly locked with the annual cycle. The linkages with the tropical water vapor transport, MJO, BSISO and the extremely wet/dry seasons will be discussed.

The monsoon development in the early rainy season in East Asia is analysed by the evolution of daily weather types (WTs). The WTs are classified by a k‐means clustering analysis based on 850 hPa winds from April 1 to July 31 in the 40‐year period of 1979–2018. Five WTs are identified, typifying the progression of weather regimes in the monsoonal evolution. WTs 1 and 2, with easterly winds in the South China Sea (SCS), occurs mostly in April and early May, corresponding to typical WTs before the SCS monsoon onset. In WT3, winds in the SCS turns westerly, and a rain band emerges in South China, extending east‐northeastward to the Pacific Ocean south of Japan, which signifies the May–June Mei‐yu in South China. Then, with the rain band moved to Yangtze River Valley (YRV) in WT4, this WT corresponds to the June–July Mei‐Yu in central and eastern China along the YRV. Finally, WT5 occurs more frequently towards the end of July, and corresponds to the post‐Mei‐Yu WT, indicating the ending of the early summer rainfall season in East Asia. The evolution of the WTs is gradual but intermittent, representing the weather‐within‐climate information. Each WT likely persists to itself. But WT1 and WT2 also progress to each other. The long persistence of WT3 and WT4 up to several weeks indicates the quasi‐stationary Mei‐Yu in South China and the YRV, respectively. The year‐to‐year variability of the WTs is also evident in the WTs. The El Niño–Southern Oscillation (ENSO) impact on the precipitation in the East Asian region is analysed for three types of ENSO: Eastern Pacific, Central Pacific, and mixed El Niño and La Niña. The seasonal mean precipitation anomalies can be interpreted by the frequencies of the daily WTs under different ENSO conditions.

AbstractIn the boreal summer of 2022, Pakistan suffered record rainfall that led to severe flooding and left more 30 million people homeless. At the same time, a severe heatwave persisted over central China. The concurrence of these extreme events suggests a possible linkage. Our analysis of climatic data indicated that the record rainfall was triggered by an extratropical cold-dry northerly associated with European blocking interacting with an unusually strong warm-moist southerly flow from the Arabian Sea at Pakistan. Both flows joined with an easterly anomaly induced by La Niña over the northern Indian subcontinent, which resulted in strong convergence. Wave activity flux analysis indicated that the European blocking, flooding in Pakistan, and heatwave in China were teleconnected by a stationary Rossby wave-like pattern. The rainfall in Pakistan may have induced diabatic heating that forced an upper-level anomalous anticyclone downstream and strengthened the heatwave in central China.

During the austral summer 2018/19, devastating floods occurred over northeast Australia that killed approximately 625,000 head of cattle and inundated over 3000 homes in Townsville. In this paper, the disastrous event was identified as a record-breaking subseasonal peak rainfall event (SPRE). The SPRE was mainly induced by an anomalously strong monsoon depression that was modulated by the convective phases of an MJO and an equatorial Rossby (ER) wave. The ER wave originated from an active equatorial deep convection associated with the El Niño warm sea surface temperatures near the dateline over the central Pacific. Based on the S2S Project Database, we analyzed the extended-range forecast skill of the SPRE from two different perspectives, the monsoon depression represented by an 850-hPa wind shear index and the 15-day accumulated precipitation characterized by the percentile rank (PR) and the ratio to the three-month seasonal (DJF) totals. The results of four S2S models of this study suggest that the monsoon depression can maintain the same level of skill as the short-range (3 days) forecast up to 8–10 days. For precipitation parameters, the conclusions are similar to the monsoon depression. For the 2019 northern Queensland SPRE, the model forecast was, in general, worse than the expectation derived from the hindcast analysis. The clear modulation of the ER wave that enhanced the SPRE monsoon depression circulation and precipitation is suspected as the main cause for the lower forecast skill. The analysis procedure proposed in this study can be applied to analyze the SPREs and their associated large-scale drivers in other regions.

Taiwan and Philippine (TWPH) (117 129 degrees E, 5 26 degrees N) is a region with most frequent and intense tropical cyclone (TC) influence in the world. This paper documents the climatology and variability of TWPH TC activity with specific attention to the difference in the TCs formed over the western North Pacific (WNP) and over the South China Sea (SCS). The spatial characteristics of TWPH TCs are analyzed based on the accumulated cyclone kinetic energy (ACE) in four sub-areas where distinctly different TC seasonality and variability is found. Different from over the broad Northwest Pacific Basin (0 60 degrees N, 100 degrees E 180 degrees) where the WNP-born TC frequency dropped sharply in late-1990s and the SCS-born TC frequency slightly increased in mid-1990s, over TWPH three distinct epochs are identified. A weak variability epoch occurred during 1979 1996, a persistent low-ACE epoch during 1997 2002, and a more variable epoch during 2003 2018. The second epoch is most noteworthy. The unusually weak TC activity during this period in particular over the Philippines was associated with anomalously strong anticyclone over the SCS and the Philippine Sea during the East Asian summer monsoon season. The strong anticyclonic circulation appeared as a descending leg of the enhanced East Asian summer monsoon during summer (July to September). During autumn and early winter (September to December) the Philippine Sea anticyclone was interpreted as the descending Rossby wave response to the suppressed convection over tropical western Pacific. The anomalous anticyclone strengthened the low-level confluent flow and convection over the SCS. The findings are useful to real-time TWPH TC activity monitoring and analysis.

Rainfall over South China Sea (SCS)-Maritime Continent (MC) region involves multiple-scale phenomena such as the annual cycle, monsoon variability, ENSO, Madden-Julian Oscillation (MJO), and convectively coupled equatorial waves (CCEWs). This study focuses on documenting MJO and CCEW modulation on the boreal winter subseasonal peak precipitation, which is an event with maximum 15-day accumulated rainfall amount during November to February, summarized at 10 by 10 degrees of longitude and latitude box areas in the region. It turns out that MJO shows strong influence on the peak event occurrence time. However, MJO has almost no positive effect on the peak event in the near equator land area. Mixed Rossby-gravity wave and tropical disturbance (MT) and equatorial Rossby (ER) wave show strong positive modulation on peak rainfall mean intensity. Cases during the SCS Two Island Monsoon Experiment (SCSTIMX) winters (2016/17 and 2017/18) are analyzed. To the north of 5 degrees N, the peak event in 2016/17 occurred concurrently with MJO convective phase, while in 2017/18 as lack of MJO activity the occurrence time was modulated by the ER wave. The 2016/17 peak event shows weaker mean rainfall intensity than the 2017/18 event. To the south of 5 degrees N, the area-mean peak event occurrence time was delayed in 2016/17, while the intensity was enhanced by the joint modulation of MJO, Kelvin and ER waves. The importance of understanding the area-mean and within-area-difference of peak rainfall events in the SCS-MC region was discussed. The findings can be applied to assess the subseasonal predictability of dynamical forecast models.

The seasonal transition from December 2017 to May 2018 occurred during the final decaying stage of the La Nina phase following the 2015/16 El Nino. In this report we documented the anomalous cyclonic flow that persisted over the South China Sea (SCS) in winter and over the western North Pacific in spring was maintained by the anomalous heating in the equatorial Pacific and the extratropical influences that consist of weakened Aleutian low and subtropical wind-SST coupled air-sea fluxes over the NW Pacific. Persistent anomalous north-easterlies along with negative OLR and warm SST anomalies over the SCS in spring was found to be sustained by the cold and dry air adverted from East Asia into the lower latitudes through the anomalous easterlies associated with the cyclonic flow to the south and anticyclonic flow to the north at 20 - 30 degrees N. Besides the above interannual scale influences, heating over tropical Indian Ocean (IO) associated with two intra-seasonal oscillation (ISO) episodes in April and May caused strong easterly flow over eastern IO and Maritime Continent. The interannual and intra-seasonal influences together maintained an anticyclonic flow from SCS to Bay of Bengal in April and May, and delayed the SCS monsoon onset. A dry Equatorial Rossby wave that arrived at the SCS in late May further enhanced the delay and resulted in a late SCS monsoon onset in early June.

BACKGROUND:Extreme temperature events have been observed to appear more frequently and with greater intensity in Taiwan in recent decades due to climate change, following the global trend. Projections of temperature extremes across different climate zones and their impacts on related mortality and adaptation have not been well studied. METHODS:We projected site-specific future temperature extremes by statistical downscaling of 8 global climate models followed by Bayesian model averaging from 2021 to 2060 across Taiwan under the representative concentration pathway (RCP) scenarios RCP2.6, RCP4.5, and RCP8.5. We then calculated the attributable mortality (AM) in 6 municipalities and in the eastern area by multiplying the city/county- and degree-specific relative risk of mortality according to the future population projections. We estimated the degree of adaptation to heat by slope reduction of the projected AM to be comparable with that in 2018. RESULTS:The annual number of hot days with mean temperatures over 30 °C was predicted to have a substantial 2- to 5-fold increase throughout the residential areas of Taiwan by the end of 2060 under RCP8.5, whereas the decrease in cold days was less substantial. The decrease in cold-related mortality below 15 °C was projected to outweigh heat-related mortality for the next two decades, and then heat-related mortality was predicted to drastically increase and cross over cold-related mortality, surpassing it from 2045 to 2055. Adjusting for future population size, the percentage increase in heat-related deaths per 100,000 people could increase by more than 10-fold under the worst scenario (RCP8.5), especially for those over 65 years old. The heat-related impacts will be most severe in southern Taiwan, which has a tropical climate. There is a very high demand for heat-adaptation prior to 2050 under all RCP scenarios. CONCLUSIONS:Spatiotemporal variations in AM in cities in different climate zones are projected in Taiwan and are expected to have a net negative effect in the near future before shifting to a net positive effect from 2045 to 2055. However, there is an overall positive and increasing trend of net effect for elderly individuals under all the emission scenarios. Active adaptation plans need to be well developed to face future challenges due to climate change, especially for the elderly population in central and southern Taiwan.

Summer days with extremely hot temperatures in Taiwan have been increasing for the past few decades, and this continuing trend is expected to worsen heat-related mortality. To mitigate the corresponding health impacts, in this study, we developed a statistical state-space model to predict the number of extremely hot days in June-September for the next year. Based on historical data from 1951 to 2017, we estimated the climate change trend after adjusting for the nonlinear lagged effect of the Niño 3.4 index. We then developed a predictive state-space model using these two primary factors and adjusting for residual autocorrelations. Validation results comparing the extremely hot days observed over 2015-2017 with predictions showed that 86% of the average prediction errors were within 4 days of the observations. To assess the health impacts, we applied the model to the projection of heat-attributable mortality (AM) in 2018 by adopting a comparative risk assessment (CRA) approach with the reference period of 2001-2010. The results showed that the Taipei metropolitan area in northern Taiwan is the most affected region with AM of 1501 deaths from all-causes, followed by Taichung in central Taiwan with 490 deaths. The prediction model and the CRA projection provide both a tool and guidance for public health administrators to address the imminent threat posed by climate change.