Radar-based Characteristics and Formation Environment of Supercells in the Landfalling Typhoon Mujigae in 2015

This study presents the radar-based characteristics and formation environment of supercells spawned by the tornadic landfalling Typhoon Mujigae(2015)in October 2015.More than 100 supercells were identified within a 24-hour period around the time of the typhoon’s landfall,of which three were tornadic with a rotational intensity clearly stronger than those of non-tornadic supercells.The identified supercells were concentrated within a relatively small area in the northeast quadrant beyond 140 km from the typhoon center.These supercells were found more likely to form over flat topography and were difficult to maintain in mountainous regions.During the study period,more supercells formed offshore than onshore.The mesocyclones of the identified supercells were characterized by a small diameter generally less than 5 km and a shallow depth generally less than 4 km above ground level.An environmental analysis revealed that the northeast quadrant had the most favorable conditions for the genesis of supercell in this typhoon case.The nondimensional supercell composite parameter(SCP)and entraining-SCP(E-SCP)were effective in separating supercell from non-supercell environment.Even though the atmosphere in the typhoon’s northeast quadrant was characterized by an E-SCP/SCP value supportive of supercell organization,orography was an impeditive factor for the supercell development.These findings support the use of traditional parameters obtained from midlatitude supercells to assess the supercell potential in a tropical cyclone envelope.

Science and prediction of monsoon heavy rainfall

With the increasing incidence of heavy rainfall events,particularly over the monsoon regions,the highly dense populations are more vulnerable[1].Research initiatives on observation,modeling,and prediction of monsoon heavy rainfall have been promoted actively by World Weather Research Programme's(WWRP)Working Group on Tropical Meteorology Research(WGTMR)of the World Meteorological Organization(WMO)since 2010.Series of monsoon-heavy-rainfall workshops were held in Beijing(2011),Petaling Jaya(2012),and New Delhi(2015)to benefit scientists worldwide and forecasters from the National Meteorological and Hydrological Services.An international Research and Development Project,namely,the Southern China Monsoon Rainfall Experiment(SCMREX)[2]was established in 2013 to coordinate field campaign experiments and to conduct scientific research on presummer(April-June)heavy rainfall processes in southern China.

A REVIEW OF THE STORM CHARACTERISTICS OF TYPHOON KALMAEGI (1415) AND RELATED FORECASTING CONSIDER ATIONS IN HONG KONG

Kalmaegi(1415)required the issuance of Gale or Storm Wind Signal No.8 in Hong Kong in 2014,even though it passed by at a distance of 370 km from Hong Kong during its closest approach.Storm surges triggered by Kalmaegi caused backflow of sea water in some low lying areas in both Hong Kong and Macao.This paper reviews the use of observational data in monitoring the cyclone characteristics and studies the synoptic factors leading to its fast movement and extensive circulation.The combined analysis of multi-platform satellite wind retrieval,in-situ surface observations and aircraft reconnaissance data over the northern part of the South China Sea is found to be useful in depicting the cyclone structure.Synoptic analysis suggests that the relatively large size of Kalmaegi may be attributed to monsoon shear pattern during its formation stage and the subsequent strengthening of southwesterlies over the northern part of the South China Sea.A strong subtropical ridge north of Kalmaegi not only provides strong steering and thus its high translational speed,but also leads to extensive gale force wind distribution over its northern semi-circle.The performance of various numerical prediction models in forecasting the movement,intensity change and wind structure of Kalmaegi,as well as the storm surge triggered,is assessed and presented.

PROGRESS IN HONG KONG'S TROPICAL CYCLONE FORECASTING AND WARNING SERVICES IN RECENT DECADES

With modern infrastructures and effective warning systems,casualties,damages and losses due to tropicalcyclones(TCs)have been significantly reduced over the years in Hong Kong.Nevertheless,densely populated coastal cities like Hong Kong will need to continuously enhance its resilience to high winds,heavy rain and storm surges brought by TCs,especially with the growing concern of the challenges induced by climate change and sea level rise.By embracing the advance of remote sensing,communication and numerical modelling technology,the Hong Kong Observatory(HKO)continues to improve its TC monitoring and forecasting techniques as well as forecasting and warning services to meet the needs of the society.This paper concisely reviews the major development and achievement of TC-related operation and services of HKO in recent decades,in aspects such as Numerical Weather Prediction(NWP)models,nowcasting techniques,warning communication and public education.Future thrusts on TC forecasting and warning services of HKO will also be discussed.