The western North Pacific subtropical high (WNPSH) dominates the summer climate over East Asia. The intensity, position, and shape of WNPSH influence the spatiotemporal distributions of precipitation, temperature, and tropical cyclone activities in this region. This paper intends to investigate the performance of the UK Met Office Global Seasonal forecast system version 5 (GloSea5) in simulation/prediction of the WNPSH based on a hindcast dataset. Analyses of the hindcast data show a systematic bias in the mean circulation over West Pacific, with negative geopotential height anomalies over the western North Pacific (WNP) and cyclonic anomalies in the 850-hPa winds and water vapor transport, indicating a weakening and eastward shift of the WNPSH. Despite the model’s bias in the climatology, it well captured the interannual variability of the monthly and seasonal-mean intensity of the WNPSH and the position of its ridge line in boreal summer from 1993 to 2015. The seasonal hindcasts indicate that there is significant prediction skill at up to three-month lead time for both the intensity and position of the WNPSH ridge line. The relationship between the WNPSH and different phases of the El Niño-Southern Oscillation (ENSO) in both the observational data and GloSea5 hindcasts was then investigated. The model captured the summer WNPSH anomalies well during most of the ENSO phases, except in the La Niña decaying and neutral summers. The intensity of the anticyclone in the WNP is weak in the decaying phase of El Niño in the GloSea5 hindcasts compared with the reanalysis data. GloSea5 is capable of representing the lagged teleconnection between El Niño events in the previous winter and the intensity of the WNPSH in the following summer. Regression analysis reveals weakened negative sea surface temperature anomalies (SSTAs) over the WNP in GloSea5, which reduced the gradient between the tropical western Pacific and the tropical Indian Ocean, resulting in a weaker easterly anomaly and stronger westerly anomaly, contributing to the weak anomalous anticyclone over the WNP and the weakened WNPSH relative to the reanalysis data.

北太平洋副热带高压西部（WNPSH）主导着东亚的夏季气候。WNPSH的强度，位置和形状影响该地区降水，温度和热带气旋活动的时空分布。本文旨在研究英国气象局全球季节性预报系统版本5（GloSea5）在基于后验数据集的WNPSH的模拟/预测中的性能。对后播数据的分析表明，西太平洋的平均环流存在系统性偏差，北太平洋西部（WNP）的负势势高度异常以及850-hPa的风和水汽输送的气旋异常，表明减弱和向东移动WNPSH。尽管该模型在气候方面存在偏见，它很好地捕获了WNPSH在1993年至2015年夏季的WNPSH的月度和季节平均强度的年际变化及其脊线的位置。季节后遗症表明，在长达三个月的提前期之前，它具有显着的预测能力WNPSH脊线的强度和位置。然后研究了观测资料和GloSea5后预报中的WNPSH与厄尔尼诺-南方涛动（ENSO）不同相位之间的关系。该模型在ENSO的大多数阶段都很好地捕获了夏季WNPSH异常，但拉尼娜衰落和中性夏季除外。与重新分析的数据相比，在GloSea5后代的厄尔尼诺现象的衰变阶段，WNP中反气旋的强度很弱。GloSea5能够表示前一个冬季的厄尔尼诺事件和下个夏季的WNPSH强度之间的滞后遥相关。回归分析显示，GloSea5 WNP上的负海面温度距平（SSTAs）减弱，这减小了热带西太平洋和热带印度洋之间的梯度，导致东风偏弱和西风偏强，导致了弱的反气旋异常相对于重新分析数据而言，WNP和WNPSH减弱。