RECENT ADVANCES IN RESEARCH AND FORECASTING OF TROPICAL CYCLONE TRACK, INTENSITY, AND STRUCTURE AT LANDFALL

This review prepared for the fourth International Workshop on Tropical Cyclone Landfall Processes(IWTCLP-4) summarizes the most recent(2015-2017) theoretical and practical knowledge in the field of tropical cyclone(TC) track, intensity, and structure rapid changes at or near landfall. Although the focus of IWTCLPIV was on landfall, this summary necessarily embraces the characteristics of storms during their course over the ocean prior to and leading up to landfall. In the past few years, extremely valuable observational datasets have been collected for TC forecasting guidance and research studies using both aircraft reconnaissance and new geostationary or low-earth orbiting satellites at high temporal and spatial resolution. Track deflections for systems near complex topography such as that of Taiwan and La Réunion have been further investigated, and advanced numerical models with high spatial resolution necessary to predict the interaction of the TC circulation with steep island topography have been developed. An analog technique has been designed to meet the need for longer range landfall intensity forecast guidance that will provide more time for emergency preparedness. Probabilistic track and intensity forecasts have also been developed to better communicate on forecast uncertainty. Operational practices of several TC forecast centers are described herein and some challenges regarding forecasts and warnings for TCs making landfall are identified. This review concludes with insights from both researchers and forecasters regarding future directions to improve predictions of TC track, intensity, and structure at landfall.

MIND THE GAP: TOWARDS AND BEYOND IMPACT MESSAGING TO ENHANCE TROPICAL CYCLONE RISK COMMUNICATION

Traditionally, meteorological agencies collect, analyse, and share technical information about natural hazards with emergency services organisations and community members; often sending different warning products to each of these groups. For the general public, effective risk communication requires that technical information be translated to first gain attention and build understanding of risk, and then continue to be exchanged by all parties. The World Meteorological Organization and its partner agencies have recognised this need for translated information by moving away from warnings describing risks solely in terms of meteorological parameters and towards clearer messaging emphasizing significance and potential impacts. While the move towards more relatable weather warning messaging is a positive one, risk communication is a complex, dynamic and interactive process that is highly dependent on audience psychology, knowledge, skills, and capabilities; presenting at once difficulties and opportunities for agencies. Over recent years, advertisers, politicians and public safety advocates have all improved their messaging through the use of big data, psychology, social networking and behavioural economics principles, yet the links between these elements and weather risk communication are still relatively immature. This report aims to build links between weather forecasters, social scientists and related industries by outlining three conceptual models social scientists have developed to meet different challenges in the field of risk communication; the mental models approach, risk information seeking and processing, and the protective action decision making model. Recent issues and successes in the communication of tropical cyclone risk will then be examined and compared to these models, and future opportunities will be discussed.

THE WORLD METEOROLOGICAL ORGANIZATION FOURTH INTERNATIONAL WORKSHOP ON TROPICAL CYCLONE LANDFALL PROCESSES(IWTCLP-IV): A SUMMARY

The Fourth International Workshop on Tropical Cyclone Landfall Processes(IWTCLP-4) was held in Macao, China from 5-7 December 2017. The workshop was organized by the World Meteorological Organization(WMO) Expert Team on Tropical Cyclone Landfall Processes in partnership with the WMO Tropical Cyclone Program. The workshop provided a forum for discussion between researchers and forecasters on the current status of tropical cyclone landfall processes and on priorities and opportunities for research. More than 60 leading research scientists and warning specialists working on topics related to tropical cyclone landfall examined current knowledge, forecasting and research trends from an integrated global perspective. The workshop offered a number of recommendations for future forecasting studies and research with special regard to the varying needs of different tropical cyclone af fected regions. The recommendations emanating from the workshop will be presented at the upcoming Ninth International Workshop on Tropical Cyclones(IWTC-9)(Hawaii, USA, 3-7 December 2018).

TROPICAL CYCLONE WIND FIELD DETERMINATION:CHALLENGES AND POSSIBILITIES

The difficulties encountered in trying to determine the intensity of any landfalling tropical cyclone are reviewed. These difficulties are then related to the complexities observed during the landfall of Severe Tropical Cyclone Larry(2006), and possible wind speed sampling deficiencies and biases are considered for that event. Recent and expected advances in knowledge of storm structure and wind speed estimation methods suggest a need for increased documentation requirements, so that the various assumptions employed in estimating landfall intensity can subsequently be improved upon. Increases in documentary requirements may also improve the error bound determination of intensity estimates of individual events, and thus ultimately the climate record as well.

THE CONVECTIVE FEATURES WITHIN AND SURROUNDING SEVERE TROPICAL CYCLONE LARRY(2006)

A sequence of ground-based radar reflectivity images sampled in the 17 hours prior to, and during the landfall of Severe Tropical Cyclone Larry(2006) are presented and analyzed using Fourier and wavelet analysis techniques. A range of mesoscale convective anomalies were detected, with characteristics and behavior consistent with vortex Rossby wave initiation. Cyclonically propagating eye-wall kinks, elongations and mesoscale reflectivity maxima were all observed throughout the sampling period, along with intense inner spiral bands. Various deep convective maxima propagated within the eye-wall at speeds consistent with predictions derived by linear barotropic wave theory. Three eye-wall breakdown episodes were observed during the study period, along with corresponding increases in storm-core asymmetric wave power and reductions in estimated storm intensity. Vortex Rossby wave initiated radial flows are also suggested by the presence of a possible mesovortex within a broken section of the eye-wall during landfall, and the outward ejection of filaments of deep convection from an adjacent inner spiral band. The possible influence of this wave activity upon the storm intensity and integrity is discussed.