A Climatology of Heavy Rain and Major Flood Events in Victoria 1876-2019 and the Effect of the 1976 Climate Shift

An extensive search has been carried out to find all major flood and very heavy rainfall events in Victoria since 1876 when Southern Oscillation(SOI)data became available.The synoptic weather patterns were analysed and of the 319 events studied,121 events were found to be East Coast Lows(ECLs)and 82 were other types of low-pressure systems.Tropical influences also played a large role with 105 events being associated with tropical air advecting down to Victoria into weather systems.Examples are presented of all the major synoptic patterns identified.The SOI was found to be an important climate driver with positive SOIs being associated with many events over the 144 years studied.The 1976 Climate Shift and its influence on significant Victorian rainfall events is studied and negative SOI monthly values were shown to dominate following the Shift.However,one of the most active periods in 144 years of Victorian heavy rain occurred after the shift with a sustained period of positive SOI events from 2007 to 2014.Therefore,it is critical for forecasting future Victorian heavy rainfall is to understand if sequences of these positive SOI events continue like those preceding the Shift.Possible relationships between the Shift and Global Temperature rises are also explored.Upper wind data available from some of the heaviest rainfall events showed the presence of anticyclonic turning of the winds between 850hPa and 500hPa levels which has been found to be linked with extreme rainfall around the Globe.

A SHORT NOTE ON THE RAPID INTENSIFICATION OF HURRICANES HARVEY AND IRMA

Hurricanes Harvey and Irma had a huge impact on the Southern United States and in the case of Irma,also parts of the Caribbean Islands.Here we focus on the impact of both hurricanes following a period of rapid intensif ication.The structure of hurricanes were examined using wind data made available from aircraft reconnaissance missions.Intense convection developed in a region where the winds in the lower to middle levels turned anticyclonically with height.Earlier studies showed that this wind structure was similar to that would be found in an ascent region theoretically associated with Quasi-Geostrophic warm air advection.

THE INTERACTION OF HURRICANE MICHAEL WITH AN UPPER TROUGH LEADING TO INTENSIFICATION RIGHT UP TO LANDFALL

Hurricane Michael was intensifying as it made landfall devastating areas of the Florida Panhandle including the small town of Mexico Beach. The structure of the hurricane is examined using radar wind data made available from aircraft reconnaissance missions. This showed a dominant warm air advection configuration(winds turning in direction in an anticyclonic fashion with height) around the core of the hurricane. Conventional radiosonde data was also used to study the warm air advection environment east of a deep layered tough system which Michael moved into and which appeared to favour such strong intensification. The structure of this deep trough is also examined and compared with a situation where Hurricane Dennis in 2005 weakened as it approached the coast in much the same region. It appears that the thermal structure of the upper trough at low to middle levels is critical to whether the hurricane intensifies or weakens with the presence of strong cold air advection associated with weakening.

The interaction of Hurricane Michael with an upper trough leading to intensification right up to landfall

Hurricane Michael was intensifying as it made landfall devastating areas of the Florida Panhandle including the small town of Mexico Beach.The structure of the hurricane is examined using radar wind data made available from aircraft reconnaissance missions.This showed a dominant warm air advection configuration(winds turning in direction in an anticyclonic fashion with height)around the core of the hurricane.Conventional radiosonde data was also used to study the warm air advection environment east of a deep layered tough system which Michael moved into and which appeared to favour such strong intensification.The structure of this deep trough is also examined and compared with a situation where Hurricane Dennis in 2005 weakened as it approached the coast in much the same region.It appears that the thermal structure of the upper trough at low to middle levels is critical to whether the hurricane intensifies or weakens with the presence of strong cold air advection associated with weakening.

Forecasting tropical cyclone tornadoes and impacts:Report from IWTC-X

This report synthesizes global tropical cyclone(TC)tornado research and operational practices to date.Tornadoes are one of the secondary(and lesser researched)hazards contributing to the devastation TCs leave in their wake.While gale-force winds and storm surge produce the majority of damage and fatalities globally,TC tornadoes also pose a fatal threat,complicating evacuation plans and protective actions as the storm moves inland.Climatological studies characterize TC-spawned tornadoes as usually weak and short-lived,primarily originating from miniature supercells in the outer rainbands.These tornadic features pose challenges to forecasting and radar detection.Additionally,TC tornadoes can pose a threat to communities 12 h prior to and beyond 48 h after a TC makes landfall.Research,both basic and operational,has increased globally over the last few years in efforts to move from a climatological to ingredientsbased approach to detect and forecast TC tornadoes.While the United States has led the charge,given the increased exposure to tornadoes year round,other nations such as China,Japan,and Australia have increased their efforts to record and detect TC tornadoes.Despite these advancements,more work needs to be done globally to understand the TC environment conducive for tornadic activity.Recommendations for future forecasting and research for TC tornadoes include i)develop a comprehensive global tornado database to improve research and forecasting efforts;ii)apply innovative technology to detect tornadoes;and iii)conduct field campaigns to thoroughly sample TC tornado environments,particularly along coastlines.

ADVANCES IN UNDERSTANDING AND FORECASTING RAPIDLY CHANGING PHENOMENA IN TROPICAL CYCLONES

This review of new understanding and forecasting of tropical cyclones(TCs) is based on presentations at the International Top-level Forum on Rapid Change Phenomena in Tropical Cyclones in Haikou, China. The major topics are the sudden changes in tracks, rapid changes in structure and intensity, rapid changes in rainfall, and advances in forecasting and forecaster requirements. Although improved track forecast guidance has been achieved with the Australian ACCESS-TC model and in track forecasts to 120 h by the China Meteorological Administration, there is a continuing need for better understanding and improved track forecast guidance. Advances in understanding of processes related to rapid intensification(RI), secondary eyewall formation, mechanisms controlling inner-core structure and size changes, and structure and intensity changes at landfall have been achieved, but progress in prediction of rapid changes in structure and intensity has been slow. Taking into account complex interactions involved in TC-related rainfall, a prioritized list of physical processes that govern rainfall from landfalling TCs in China has been developed. While forecaster participants were generally encouraged by the progress being made, they expressed a strong desire for a transition of that new knowledge to timely and reliable forecast guidance products.

Extreme rainfall and flooding from Hurricane Florence

Hurricane Florence made landfall near Wrightsville Beach,North Carolina,around 1115 UTC 14 September as a weakening Category 1 hurricane(on the Saffir-Simpson Hurricane Wind Scale).Its slow movement through North and South Carolina resulted in extreme rainfall totals and major flooding making it the ninth-most-destructive hurricane to affect the United States.The structure of Florence is examined using microwave data,radiosonde observations and rainfall registrations to identify the processes along with its slow movement which caused the extreme rainfall.Two major processes were identified with initially,intense thunderstorms driven by strong buoyancy with some dynamic uplift,generated such rainfall while following landfall larger scale ascent with winds turned in an anticyclonic direction with height,appeared to be the principal cause of the heavy rainfall.