A DEVELOPMENTAL FRAMEWORK FOR IMPROVING HURRICANE MODEL PHYSICAL PARAMETERIZATIONS USING AIRCRAFT OBSERVATIONS

As part of NOAA’s Hurricane Forecast Improvement Program(HFIP),this paper addresses the important role of aircraft observations in hurricane model physics validation and improvement.A model developmental framework for improving the physical parameterizations using quality-controlled and post-processed aircraft observations is presented,with steps that include model diagnostics,physics development,physics implementation and further evaluation.Model deficiencies are first identified through model diagnostics by comparing the simulated axisymmetric multi-scale structures to observational composites.New physical parameterizations are developed in parallel based on in-situ observational data from specially designed hurricane field programs.The new physics package is then implemented in the model,which is followed by further evaluation.The developmental framework presented here is found to be successful in improving the surface layer and boundary layer parameterization schemes in the operational Hurricane Weather Research and Forecast(HWRF) model.Observations for improving physics packages other than boundary layer scheme are also discussed.

RECENT ADVANCES IN RESEARCH AND FORECASTING OF TROPICAL CYCLONE RAINFALL

In preparation for the Fourth International Workshop on Tropical Cyclone Landfall Processes(IWTCLP-IV), a summary of recent research studies and the forecasting challenges of tropical cyclone(TC) rainfall has been prepared. The extreme rainfall accumulations in Hurricane Harvey(2017) near Houston, Texas and Typhoon Damrey(2017) in southern Vietnam are examples of the TC rainfall forecasting challenges. Some progress is being made in understanding the internal rainfall dynamics via case studies. Environmental effects such as vertical wind shear and terrain-induced rainfall have been studied, as well as the rainfall relationships with TC intensity and structure. Numerical model predictions of TC-related rainfall have been improved via data assimilation, microphysics representation, improved resolution, and ensemble quantitative precipitation forecast techniques. Some attempts have been made to improve the verification techniques as well. A basic forecast challenge for TC-related rainfall is monitoring the existing rainfall distribution via satellite or coastal radars, or from over-land rain gauges. Forecasters also need assistance in understanding how seemingly similar landfall locations relative to the TC experience different rainfall distributions. In addition, forecasters must cope with anomalous TC activity and landfall distributions in response to various environmental effects.

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).

Research advances on internal processes affecting tropical cyclone intensity change from 2018–2022

This contribution summarizes the significant progress in a variety of topic areas related to internal tropical cyclone(TC)intensity change processes over 2018–2022 from the WMO Tenth International Workshop on Tropical Cyclones(IWTC-10).These topic areas include surface and boundary layer processes;TC internal structure and microphysical processes;and,radiation interactions with TCs.Recent studies better frame the uncertainty in the surface drag and enthalpy coefficients at high wind speeds.These parameters greatly impact TC intensity and it is therefore important that more direct measurements of these boundary layer parameters are made.Particularly significant scientific strides have been made in TC boundary layers.These advancements have been achieved through improved coupled models,large-eddy simulations,theoretical advance-ments,and detailed observations.It is now clear that the research field needs to better represent the eddy viscosity throughout the depth of the boundary layer.Furthermore,detailed study of coherent structures in TC boundary layers will likely be a propitious direction for the research community.Meanwhile,in-depth observational field campaigns and assiduous data analysis have made significant headway into verifying theory and modeling studies of intensification processes related to TC vortex alignment,efficient latent heating distributions,and overall 3D structure.Substantial efforts have also been made to better understand the intricate roles radiative processes play in TC evolution and intensity change.Finally,some promising progress has been made in the development of time-dependent theories of TC intensification and the predictability of internal TC intensity change.Overall,there have been well-earned gains in the understanding of intensity change processes intrinsic to the TC system,but the journey is not complete.This paper highlights some of the most relevant and important research areas that are still shedding new light into internal factors governing TC intensity change.