This paper reports on a waterspout presiding over the Pearl River Estuary near Zhuhai, China. It is observed mainly using the terminal Doppler weather radar in Hong Kong. A slanting radar reflectivity core and airflow circulating around was seen in the vertical cross-section across the mesoscale/microscale cyclone associated with the waterspout. The vertical wind profile associated with the cyclone was analysed and found to exhibit characteristics similar to those of a tornado reported in the region in a previous study. The primary characteristic of the waterspout was a circulating flow stronger at higher levels (approximately a few kilometres above ground) than at lower levels. In terms of nowcasting, the performance of a convection-permitting numerical weather prediction model (2 km horizontal resolution) was analysed. It was found to demonstrate reasonable simulation skill for the mesoscale/microscale cyclone, although the slanting feature was not well predicted. The results of this study can serve as a useful reference for similar studies of waterspouts/tornadoes worldwide. K E Y W O R D Snumerical simulation, waterspout, weather radar

An observational and simulation study of a tornado event in Hong Kong that occurred in the morning of 29 August 2018 is documented in this paper. Rotating airflow associated with the tornado is well captured by the Doppler velocity from a Terminal Doppler Weather Radar (TDWR) in Hong Kong. The Doppler velocity patterns show the typical signature of a velocity couplet associated with a meso/microcyclone, and for most part of its lifetime, it captures clearly the evolution with time. Weather radar echoes of those thunderstorms inducing the current tornado, as well as the meso/microcyclone itself, are also successfully reproduced in a real-time simulation by a fine-resolution numerical weather prediction (NWP) model initialised 3 hours earlier, albeit with a time lag of about 15 minutes when compared to the actual event. The model simulation displays some interesting features of the cyclone, including the vertical structure of horizontal and vertical velocities and cloud liquid water content, which are consistent with literature that accounts in other parts of the world. The vertical profile of maximum radial velocity associated with the velocity couplet also compares well between the actual weather radar observation and numerical simulation. The results in this paper could serve as an interesting reference for both meteorologists and wind engineers, also demonstrating the power of very high-resolution NWP in predicting such events in a real-time fashion.

Located at the southeastern coast of Guangdong Province of China, Hong Kong is susceptible to the effects of severe convective weather and tropical cyclones. The Hong Kong International Airport (HKIA) is susceptible to windshear and microbursts caused by convective weather. Due to the complex terrain around the HKIA, windshear caused by strong winds of tropical cyclones across complex terrain can be as strong as microbursts generated by thunderstorms. A Terminal Doppler Weather Radar (TDWR) has been used to detect microbursts and windshear in real time to safeguard aviation safety. The TDWR at Brothers Point, Tuen Mun, Hong Kong, was optimized to detect windshear and microbursts in a highly cluttered environment. Stationary and moving clutters were suppressed and radar velocity data were dealiased by the hybrid multiple pulse repetition interval method during radar system optimization. A case on October 4, 2015 showed that the TDWR performed satisfactorily with a probability of detection and a false alarm ratio of 91% and 1% respectively in detecting microbursts by comparing microburst features identified by the TDWR and human truth, which is a method to identify areas of interest by analysts.

ABSTRACT:In 2011, the Hong Kong Observatory (HKO) and the Government Flying Service (GFS) of the Hong Kong Government conducted reconnaissance data collection flights for two tropical cyclones over the South China Sea. It was the first time in the region that flight measurements of this kind had been carried out specifically for tropical cyclones. Horizontal wind velocity components, temperature and relative humidity at selected flight levels were recorded at the temporal resolution of 20 times per second to delineate the wind flow and other meteorological conditions. They were found to be consistent with other synoptic station data sparsely located over the sea areas, as well as in good agreement with the ocean surface wind data from the satellite microwave scatterometer. In this study, aircraft measurements for the two tropical cyclones in 2011 and one in July 2009 were assimilated into the HKO mesoscale Non-Hydrostatic Model (NHM) using its three-dimensional variational data assimilation (3DVAR) to investigate the impact of the data on the model analysis and forecast. Model sensitivity experiments with and without the flight measurements were conducted. The flight observations were found to improve model analysis and forecasts of wind circulation, temperature and humidity in the vicinity of the tropical cyclones. Improvement in track forecast was obtained although an insignificant effect was seen in predicting the central pressure of the storms. The inclusion of flight measurements also improved the forecast of the surface wind distribution and precipitation associated with the tropical cyclones.

A weak waterspout was observed at the Hong Kong International Airport on the morning of June 8, 2020. This paper documents the meteorological observations of this weak system, which was well captured by surface wind sensors and a Doppler weather radar, and this study also investigated the capability of a high‐resolution numerical weather prediction model to simulate the system in a near real‐time configuration. Despite the short‐lived nature of the vortex, the model effectively reproduced the occurrence of a weak vortex around the time the system was observed, although with positional errors of the order of a few kilometres. The simulated vertical cross‐sections of the reflectivity and Doppler velocity were consistent with the actual radar observations and reflected the slanting nature of the micro‐vortex. These results may serve as a useful reference for the study of weak waterspouts worldwide.