Understanding the Physical Processes Responsible for Different Rainfall Distributions Associated with Tropical Cyclone Landfall

Tropical cyclone (TC) is one of the most devastating weather-related hazards, which maycause significant fatalities, property loss, and damage to infrastructure, etc. when it is close to landthrough its intense winds, heavy rain and storm surge. Among these three elements, the locationof occurrence of heavy rain is the most difficult to predict because of our relative poorunderstanding of the mechanisms for the development of heavy rain associated with TCs, and thelimited amount of data available.The World Meteorological Organization therefore endorsed in 2015 the establishment of aResearch and Development Project [Understanding and Prediction of Rainfall Associated withLandfalling Tropical Cyclones (UPDRAFT)] to study the heavy rain phenomenon associated withTC landfall through field campaigns, data analyses and numerical simulations. This currentproposed project will focus on contributing to one of the two objectives of this 5-year internationalproject of which the PI is a member of the International Science Steering Committee, which is toenhance our understanding of the physical processes that lead to various rainfall distributionsassociated with TC landfall. Specifically, the objectives are as follows:(1)To document the effects of land surface characteristics and topography on the rainfalldistribution as a TC makes landfall, and(2) To identify the role of environmental thermodynamic (such as moisture and convectiveinstability) and dynamic (such as vertical wind shear) effects in modifying the rainfalldistribution.While some previous studies have addressed these two issues, they were mostly based oncase studies with limited amounts of observations, and therefore some outstanding questionsremain unanswered. The data from the field campaigns in the UPDRAFT project will allow a muchmore complete examination of the dynamic and thermodynamic conditions related to theconvection and rainfall distributions associated with TC landfall. The current proposal includesparticipation in the data collection during the field campaign, the subsequent data analyses andnumerical simulations to address the two listed objectives. While the effects listed are not the onlyones that can modify these distributions (others include, for example, large-scale synoptic flowpatterns, internal dynamics and microphysical processes), it is expected that the results of thisstudy will contribute towards an improved understanding of the physical processes responsible forthe observed rainfall distributions associated with TC landfall, which may then contribute toimproved accuracy of rainfall forecasts in numerical weather prediction models.