Tropical cyclone scenario prepared for Tonga National Emergency Management Office (NEMO) as part of the PacSAFE Project (2016-2018)

The Tropical Cyclone Scenario Selection tool enables users (e.g. emergency managers, engineers, researchers, etc.) to query the catalogue of tropical cyclone scenarios, developed as part of the 2018 Tropical Cyclone Hazard Assessment (TCHA18). The TCHA18 catalogue is comprised of 10,000 simulated years of tropical cyclone activity in the Australian region, amounting to over 160,000 tropical cyclone events. Using the search tools, the tracks and wind fields of individual events affecting a location or region can be discovered and explored. The returned scenarios are retrieved from a catalogue of synthetic tropical cyclones and can queried within the map and/or downloaded in various formats for follow-on analysis.

The National Hazard Impact Risk Service for Tropical Cyclone Event Impact provides information on the potential impact to residential separate houses due to severe winds. The information is derived from Bureau of Meteorology tropical cyclone forecast tracks, in combination with building location and attributes from the National Exposure Information System and vulnerability models to define the level of impact. Impact data is aggregated to Statistical Area Level 1, categorised into five qualitative levels of impact.

The TCHA18 Data collection covers the model output generated by the Tropical Cyclone Risk Model as part of the assessment. This includes average recurrence interval wind speeds, stochastic track catalogues, wind fields and intermediary data. It also includes an evaluation track catalogue, used to evaluate the performance of the model with respect to historical landfall rates, frequency and track density.

Tropical cyclone Gita impacted the Kingdom of Tonga in February 2018, causing significant damage across the main island of Tongatapu. This dataset is a best estimate of the maximum local gust wind speed across Tongatapu, based on the best-available track information, elevation and land cover data. The data represents the maximum 0.2 second, 10-metre above ground level wind speed at (approximately) 25 metre horizontal resolution. The wind field was generated using: Geoscience Australia's Tropical Cyclone Risk Model - https://github.com/GeoscienceAustralia/tcrm Wind Multipliers code - https://github.com/GeoscienceAusralia/Wind_Multipliers TC Gita track was sourced from the Joint Typhoon Warning Center (http://www.metoc.navy.mil/jtwc/jtwc.html)

The Tropical Cyclone Scenario Selector Tool (TC SST) provides an interactive application to interrogate the stochastic event catalogue which underpins the 2018 Tropical Cyclone Hazard Assessment (TCHA18). The application allows users to search for TC events in the catalogue based on location and intensity (either TC intensity category, or maximum wind speed), visualise the tracks and the wind fields of those events, and download the data for further analysis.

Geoscience Australia has produced a National Tropical Cyclone Hazard Assessment (TCHA18). The 1%/0.2% Annual Exceedance Probability Maps provides 0.2-second duration, 10-metre above ground level gust wind speeds across Australia arising from tropical cyclone events over a 2-km grid, for 1% and 0.2% annual exceedance probability (100- and 500-year annual recurrence interval respectively). Surface conditions are assumed to correspond to terrain category 2 conditions as defined in AS/NZS 1170.2 (2011).

The local wind multiplier data for Tongatapu is used to generate local wind speeds over the island of Tongatapu, Tonga.

The TCHA18 Stochastic Event Catalogue contains artificially generated tropical cyclone tracks and wind fields representing 10000 years of tropical cyclone activity. The catalogue stores the track of each event in annual collections (i.e. one simulated year per file). The wind field of each event is stored in a separate file, containing the maximum wind speed, the components (eastward and northward wind) corresponding to the maximum wind speed, and the minimum sea level pressure from the event. All events are recorded in a relational database file, which contains records of the distance of closest passage, maximum wind speeds and the direction of the maximum wind speed for over 400 locations in Australia. The database also contains records of the average recurrence interval wind speeds at those stations. The database is intended to simplify the process of identifying individual events in the catalogue for more detailed modelling to support scenario planning for emergency management, for example.

Consider you are responsible for providing an emergency response in Karratha. There is a category 4 cyclone sweeping towards the coast and Bureau of Meteorology forecasts indicate the cyclone will intensify to category 5 before landfall. The last time a category 5 cyclone came close to Karratha was in 1999, when Cyclone John passed 80 km east of Karratha, sparing it the worst winds. If it had not turned to the southeast prior to landfall, damage to Karratha would have been much worse. Karratha has also grown substantially since then, with close to half the residential buildings constructed after 1997. As a first responder, are you prepared for the consequences of a direct strike? Do you even know what the extent of the impacts might be? What will Karratha look like immediately after the cyclone passes? If emergency preparation decisions were based on past experience, they would likely fall well short of the required action to minimise impacts. The Severe Wind Hazard Assessment project, funded through the WA Natural Disaster Resilience Program, endeavours to provide emergency managers with realistic, modelled scenarios of cyclone impact in WA communities to inform local, regional and state planning for cyclone risk. By analysing hypothetical scenarios, the Department of Fire and Emergency Services can identify and address gaps in the understanding of the impacts of a cyclone, and improve decision-making processes at coordination and control levels. A first step in this process is to develop hypothetical severe tropical cyclone footprints for WA communities. We use a stochastic tropical cyclone model to generate a catalogue of cyclone events, then select TC tracks meeting the criteria for the exercise: events with specific intensities passing directly over communities. Here we present the hazard footprints of these hypothetical storms, and a preliminary analysis of the impacts on residential buildings. Poster presented at the 2018 Amos-ICSHMO Conference Sydney, NSW (https://www.ametsoc.org/index.cfm/ams/meetings-events/ams-meetings/amos-icshmo-2018/)