A very rare event of sand/dust weather in Hong Kong in late spring in 2025 - observational and forecasting aspects

Abstract

A rare event of sand/dust weather in Hong Kong occurred in the evening of April 12, 2025 and lasted till April 17, 2025. It is very uncommon because the sand/dust, originating from Mongolia, managed to climb over the mountains at Nanling in central-southern China with heights reaching about 2000 m above sea level, and reached the coast of southern China. Analysis of local observations confirming the occurrence sand/dust weather, namely, PM10, PM2.5/PM10 ratio, AERONET observations and chemical speciation analysis, are presented in this paper. The trajectory and thickness of the sand/dust is also studied using synoptic weather observations and geostationary meteorological satellite aerosol products. Finally, the forecasting aspect of the sand/dust weather is discussed, from the forecasting by a few days ahead to possibly at the sub-seasonal scale. It turns out that the forecast aerosol concentrations serve as a useful product to hint the occurrence of sand/dust weather in Hong Kong, even though there are still discrepancies between the observed and the forecast values. There is also signature of conditions favourable for sand/dust transport to southern China in model sub-seasonal forecast outputs, and the recurrence of similar synoptic patterns in middle and lower troposhere in late spring (April) in the future may hint the potential of sand/dust weather over Hong Kong again.