Feasibility analysis of early warning of sea fog within six hours for two harbors in the South China Sea

Sea fog significantly impacts harbor operations, at times even causing navigation to cease. This study examines two harbors in the north of the South China Sea, analyzing the feasibility of increasing each harbor's sea fog early warning capability to 6 h in advance. Although the harbors are separated by only about 100 km, analysis of their backward trajectories reveals differences in the incoming flow and sea fog types. Concerning the types, at Xuwen harbor, warm advection fog represents 49.56% of the cases, cold advection representing 48.03%. At Zhanjiang harbor, 37.06% are warm advection fog, with 58.33% cold advection fog cases. We propose different monitoring and early warning schemes for the harbors. For Xuwen, we suggest eight visibility lidars located on the north and south sides of Qiongzhou Strait (two on the north, six on the south). Here, such a setup would give warning probabilities of sea fog of 87.50, 66.23, and 49.78% for advance times of 2, 3, and 4 h. For Zhanjiang, we suggest two visibility lidars and four buoys at the east side of the harbor. The corresponding warning probabilities are 83.77, 64.47, and 47.15% for the same advance times. For 5-6 h in advance, the early warning probabilities of both harbors drop quickly. We also suggest a flow chart for the early warning and monitoring scheme at each harbor.