Doppler radar observation of Typhoon Vicente (1208) during its Rapid Intensification near landfall

Typhoon Vicente (1208) experienced an extreme rapid intensification (RI) process over the northern South China Sea (SCS) before landfalling, with its minimum sea surface pressure dropped from 975 hPa (July 23, 0600UTC) to 960 hPa (Jul 23, 1800UTC) in 12 hours and its maximum surface sustained wind increased from 33 m s-1 to 45 m s-1 according to the best track data of China Meteorological Administration (CMA). The internal processes and intensity evolution of Vicente during RI period were well revealed by Doppler Radars in Hong Kong (HKRD) for nearly 12 hours before landfalling started from 0800 UTC. The primary circulation, perturbation pressure, and reflectivity of Vicente were derived from the ground-based velocity track display (GBVTD) technique. It is interesting to note that, during the RI period, the organization process of a “secondary eyewall” was well captured by HKRD, inferring from the incipient secondary maxima in the profile of the retrieved primary circulation (SRMW) around 1500 UTC on July 23, coupled by the secondary maxima in the axisymmetric reflectivity profile. Later, the secondary eyewall contracted inward with the radius of SRMW shrinking from 67 km to 62 km within half an hour until it was interrupted and further broken down by the interaction with terrain around 1536 UTC. After that, Vicente experienced an extreme RI process shortly before landfalling accompanied by a contracting eyewall. The maxima of axisymmetric tangential wind increased from 38 m s-1 to 47 m s-1 from 1536 UTC to 1806 UTC while the radius of maximum wind (RMW) shrunk from 35 km to around 25 km. The central pressure dropped ~10 hPa in two and half hours. It was shown that RI event was coincident with high-wavenumber asymmetric energy in the northwest direction transporting inward from 80 km radius around 1600 UTC and ceasing at 40 km radius around 18 UTC.