The study on the causes of extreme hot weather in Zhejiang Province can provide scientific basis for the prediction and prevention of extreme hot weather. Based on conventional meteorological observations, the ERA5 reanalysis data from European Centre for Medium-Range Weather Forecasts, the outgoing long-wave radiation (OLR) data from National Oceanic and Atmospheric Administration, and daily climate system monitoring indices from the National Climate Center, this study compares and analyzes the spatial and temporal distribution and characteristics of two extreme high temperature events in Zhejiang Province in the summers of 2013 and 2022, and constructs a conceptual model of extreme hot weather. The results indicate that both hot events were characterized by wide coverage, long duration, strong extremity, and severe impacts. The high temperature event in 2022 had a longer duration and wider coverage area, while the single station extreme high temperature value in 2013 was higher. The western Pacific subtropical high (WPSH) in 2022 had a larger extent with a more westward ridge point, whereas in 2013, the duration of the 850 hPa warm ridge temperature exceeding 24 ℃ was longer. The center of extreme high temperature in 2022 was located farther south, with temperatures above 42 ℃ mainly occurring in central and southern Zhejiang, whereas in 2013, extreme high temperatures were concentrated in central and northern Zhejiang. The intensification and westward shift of the WPSH were the direct causes of both extreme high temperature events, corresponding well to a stronger and eastward-displaced South Asian high. When the 1 252 dagpm contour at 200 hPa extends eastward beyond 122°E, the 588 dagpm contour at 500 hPa extends westward beyond 115°E, the 850 hPa warm ridge temperature exceeds 22 ℃, and weak southerly winds prevail in the lower troposphere, it is more likely to experience extreme high temperature exceeding 40 ℃ in Zhejiang. Additionally, negative OLR anomalies over the Maritime Continent (MC) enhance the WPSH by modulating meridional vertical circulation and low-frequency wave propagation. Meanwhile, anomalous zonal vertical circulation between the Pacific at the same latitude as Zhejiang and eastern China further strengthens the WPSH. These findings provide scientific insights for predicting and mitigating extreme heat events in Zhejiang Province.

The error test of gust forecast has a certain guiding significance for the refined forecast correction in practice, and provides a reference for how to eliminate the influence of the daily variation of error in the refined forecast. The 10 m gust and 10 m average wind forecast data of the European Centre for Medium-Range Weather Forecast (ECMWF) are selected from the fine grid for 3-72 h day by day from 2017 to 2019, and based on the real maximum wind data 3 hours by 3 hours of 9 national meteorological observation stations in Dalian area, the error test of forecast is analyzed. The results are as follows: According to the forecast error test based on the forecast and the actual situation, the mean error（ME）of the ECMWF fine grid forecast is 0.96 m·s^-1, which indicates that the forecast is larger on the whole. However, the statistical conclusions of the forecast errors of the two classifications are inconsistent for each wind level, and the test according to the forecast wind level is more consistent with the actual forecast work based on the model forecast. According to the statistical test of the forecast, the forecast errors of each wind direction, each wind level and each station are obviously different. The larger the wind level is, the greater the degree of forecast bias is, and wind direction also shows the trend of error increasing with wind level increase. The average error of gust forecast has obvious daily variation, with the largest error around 08:00 and the smallest error around 20:00, which is mainly caused by the daily variation of the average error of 10 m average wind prediction. The correlation coefficients between all forecast cases and the observations for each predictive aging are above 0.7, and when it comes to each wind level and wind direction, the correlation of each wind direction is good, but the correlation of each wind level is significantly reduced, and the reliability of the wind forecast of the magnitude 8 and above is decreased greatly.

In operational weather forecast, the short-term heavy precipitation under the control of the western Pacific subtropical high is easily to be missed. In order to get a better grasp of short-term heavy rainfall in Hunan under the control of the western Pacific subtropical high and explore its causes and trigger mechanism, this paper analyzes a short-term heavy rainfall process on September 6, 2018 by using the observation data from ground automatic weather station and Doppler weather radar, retrieved TBB (black body temperature) from FY-2F satellite and NCEP reanalysis. The results show that the abundant water vapor, stronger unstable energy and certain uplift conditions can trigger the short-term heavy rainfall in Hunan Province in the ridge of the strong western Pacific subtropical high. However, it is more difficult to forecast the rainstorm due to the lack of large-scale circulation systems such as trough, middle and low level jet and shear line. Due to the invasion of weak cold air before noon, the cooperation of low-level shear with surface mesoscale convergence line cause near surface dynamic uplift, further trigger convective precipitation. In the afternoon, the surface air temperature affecting by solar radiation reaches convective triggering temperature, which can trigger freely heat convection. Both the positive vorticity region and the low-level convergence region extend upward after the rainfall, which is conducive to the maintenance of vertical upward movement, but its dynamic condition is obviously weaker than that of typical heavy precipitation process in flood season. The environmental wind and its vertical shear are weak, and the thunderstorm cells move slowly, which is beneficial to the maintenance of heavy rainfall for a long time in the same area.