In this study, 67 Tropical Cyclones (TCs) crossing Jiangsu province are identified from a total of 2440 western North Pacific TCs during the 73 a period of 1949—2021 using the best-track data archived at the China Meteorological Administration's Shanghai Typhoon Institute (CMA-STI). Temporal and spatial characteristics of activities and potential destructiveness associated with TCs crossing Jiangsu province are investigated. Results show that TCs crossing Jiangsu province, which mainly generated in July and August over a broader region, account for 2.7% and 10.2% of TCs over the western North Pacific and those making landfall in China, respectively. TCs crossing Jiangsu province made landfall in China mainly in June—November, with the highest landfalling frequency and widest landfalling distribution in August. The landfalling routes of TCs crossing Jiangsu are categorized into 14 types (T₁—T₁₄), of which the route T₄ for TCs that made landfall first in Taiwan, China and then in Fujian accounts for the highest proportion. The TC tracks crossing Jiangsu are classified into four types. The moving directions in Jiangsu and overall track morphologies of TCs corresponding to these four types are closely related to the westward extension and northward shift of the western Pacific subtropical high. TCs entered and left mainly from the southeast and east coast of Jiangsu respectively during July—September. The entering locations of TCs crossing Jiangsu shift northward from June to August and retreat southward in September—October, while leaving locations shift westward and then retreat eastward, due to seasonal adjustments of large-scale systems, such as the western Pacific subtropical high and monsoon circulation. The track density of TCs in Jiangsu generally decreases from southeast to northwest, with most of the TCs moving northward or northeastward. Spatial distributions of track density and average velocity vectors of TCs crossing Jiangsu are characterized by significant monthly variations. There is a significant increase in potential destructiveness of TCs in Jiangsu (JS-PDI) during the period of 1949—2021, corresponding to increases in their landfall intensity and average intensity in Jiangsu. The JS-PDI in August is considerably higher than in other months. In agreement with the distribution of average TC intensity in Jiangsu, larger JS-PDI values are mainly distributed in the coastal region and Southeast of Jiangsu, and the locations of maximum JS-PDI agree well with the TC track density.

Based on dual-polarization radar observations, surface data and ERA5 reanalysis product, an extensive propagation high wind event in Hubei province triggered by squall line is studied. Results show that in the environment with typical thunderstorm temperature and humidity profiles (wet downburst), the squall line originating in Southwest Henan province significantly enhanced after crossing Tongbai mountain, and resulted in a Derecho event in Hubei province. The direct reason for the enhancement of the squall line is that several isolated storms on the south side merged into the squall line. Further analysis reveals that the key mesoscale systems for the enhancement of the squall line included a shallow cold outflow from another squall line, an boundary-layer jet forced by the topography and the cold pool outflow of the squall line. The topographic effects include the blocking of cold pool outflow, the valley penetration of outflow, and the orographic uplift, which triggered isolated storms and provided a mesoscale ascending environment. After the squall line crossed the mountain, extreme winds in Guangshui were mainly caused by downward momentum transfer and divergence of strong downdrafts. The intense convective cells in the squall line were composed of graupels or small hails above the melting layer, and many small solid particles melted into large water droplets or water-covered ice cores near the melting layer. Significant evaporation under the melting layer significantly reduced the diameter of raindrops and liquid water content. This indicates that significant melting and evaporation are the main mechanisms for the formation of strong downdrafts in the storm. The results enhance our understanding of the effects of mesoscale topography on storms and physical processes of the formation of extreme winds.

To deepen understanding of mesoscale convective systems under the special topography of Hunan province, this paper uses high spatiotemporal resolution data obtained from the Variational Doppler Radar Analysis System to study the extreme precipitation process that occurred in Hunan province from 20:00 BT 29 May to 06:00 BT 30 May 2022. Results indicate that this extremely heavy precipitation event occurred in the convergence zone between dry, cold northerly airflow and warm, moist southwesterly jet at 700 hPa. In the initial stage, clustered convections were sporadically triggered and gradually organized into a banded mesoscale convection system. During the development of the banded mesoscale convection system, positive vorticity formed due to environmental vertical wind shear and negative vorticity generated by the cold pool gradually approached equilibrium, which, coupled with the enhancement of the southwesterly jet that transported a large amount of moisture, resulted in rapid development of the banded mesoscale convection system with extreme precipitation reaching 103 mm in one hour. In the maintenance stage, the compensatory downdraft for the updraft within the banded mesoscale convection system suppressed convection generation in the central part of the system. Additionally, the downdraft enhanced raindrops evaporation in the middle and lower levels and transferred horizontal westward momentum to the near-surface, intensifying convection in the eastern part of the banded mesoscale convection system and resulting in splitting of the convection system into a clustered mesoscale convective system. As the convection moved southward, the low-level southwesterly was blocked by Mingyang and Xuefeng mountains. As a result, new convections were mostly triggered on the west side of the Xiangjiang river valley, resulting in larger total precipitation there.

Back-building MCSs (Mesoscale Convective Systems) are highly conductive to sudden, localized short-duration heavy rainfall. In order to reveal the characteristics of this type of MCS and its association with heavy rainfall, this study systematically studies spatial and temporal distribution of back-building MCSs that triggered short-duration heavy rainfall during the warm seasons from 2015 to 2021 in Zhejiang province. Different organizational forms and environmental thermodynamic factors of different types are also explored. The results show that back-building MCSs in Zhejiang province exhibit significant monthly and diurnal variation patterns, i.e., MCSs mainly occur in June and July with peak hourly rainfall intensities of 30 and 50 mm in these two months, respectively. The MCS primarily form between 11:00 and 14:00 BT, with the highest frequency of formation occurring between 12:00 and 13:00 BT. The majority of MCSs have a duration of 12 h or less, with 10 h duration being the most common. The start time of backward propagation shows a quasi-bimodal pattern, which is 2—3 h later than the main formation time of the MCS. For 90% of the cases, the time of maximum hourly rainfall intensity occur within 0—2.5 h after the onset of the backward propagation. Based on the evolution characteristics of convective system organization, the back-building MCSs with short-duration heavy rainfall in Zhejiang province can be categorized into four types: Advective, quasi-stationary, turning, and propagating MCS, with about 42% occuring under the forcing of weak synoptic-scale system. The MCS usually occurs in an environment with medium convective available potential energy (CAPE), high humidity and appropriate vertical wind shear, but with different environmental factors for different types. The quasi-stationary MCSs account for the largest proportion (44.7%) and are characterized by significant environmental dynamic features, including strong atmospheric instability, large steering flow, and mid-to-lower-level vertical wind shear. They result in relatively weak maximum hourly rainfall intensity (the median is 50 mm/h). Propagating MCSs (accounting for about 17%) exhibit more distinct environmental thermodynamic characteristics with large CAPE and precipitable water (PW), and lead to the strongest maximum hourly rainfall intensity (the median is 70 mm/h).

To meet the need for weather forecasting, strong convection monitoring and warning services, an hourly 1 km wind gust product across China has been produced using hourly wind gust observations and model forecast data. These data are adopted after the procedure of quality control, space-time matching and fusion analysis. This product is updated at a 5 min lag with the overall RMSEs of 1.9 m/s for independent test and 0.68 m/s for the non-independent test. The results indicate that as the wind speed increases, the number of samples continuously declines, there is a relatively pronounced tendency for the product's error to rise, and the accuracy gradually decreases. However, the quality of this product improves effectively compared to model predictions of high speed of wind gusts. Specifically, the accuracy of wind speed above magnitude 9 has improved by 89.3%, and the relative error has dropped significantly with a reduction ratio of about 27.4%. The development of this product can support disaster mitigation and decision-making related to catastrophic gales and typhoons.

Hong Kong is a coastal city in southern China. In the nineteenth century, Hong Kong's shipping industry had been well developed, serving as an important entrepot in the region. The Hong Kong Observatory (HKO) was established in 1883. Early operations of the HKO were all related to the shipping industry at the time, including meteorological observations and tropical cyclone warning service. The HKO has been conducting meteorological measurements at its Headquarters in Tsimshatsui since 1884. The long-term weather observations document the variations of climate in Hong Kong caused by global climate change and local urbanization. In 2017, the HKO Headquarters received the World Meteorological Organization's recognition as one of the first batches of centennial observing stations in the world. In more than a century, the HKO's services have evolved in pace with the increasing expectations and requirements of the modern society. During the period, the HKO made use of advanced technologies from time to time in tandem with its operational developments. Looking ahead, the HKO will further strengthen the cooperation with meteorological authorities in mainland China and the Greater Bay Area, playing the role of connecting the world to promote close meteorological cooperations regionally and internationally, and improving the ability to prevent natural disasters and respond to emergencies.