Phenomenological and Predictability Studies of Western North Pacific Tropical Cyclones in Relation to the Pacific Jet Stream

This project will investigate tropical cyclones (TCs) over the western North Pacific with emphasis on TC life cycle, track, and structure; TC interaction with the North Pacific jet stream; and high-impact weather events over the eastern North Pacific and North America that are linked dynamically to western North Pacific TCs. Atmospheric predictability will be addressed in terms of conventional statistical measures of model forecast skill, and will be assessed in the context of episodes of individual western North Pacific TCs and downstream high-impact weather events. These project goals will be accomplished through an analysis of recurving and transitioning TCs, including those TCs that undergo extratropical transition (ET) and subsequent reintensification as extratropical cyclones (ECs), over the western North Pacific from July through December. The analysis will address the ability of operational numerical weather prediction models to forecast episodes of western North Pacific TCs and associated high-impact weather events occurring downstream over the eastern North Pacific and North America; the behavior of large-scale flow regimes in which these episodes occur; and the transitions between large-scale flow regimes that take place in conjunction with these episodes. Multiscale investigations of interactions involving TCs and the North Pacific jet stream and the ET/EC of western North Pacific TCs will be conducted to understand how initial-analysis and model-physics errors limit predictability, and will be accomplished through the synoptic evaluation of the skill of the operational National Centers for Environmental Prediction (NCEP) Global Forecast System for projections out to two weeks. This project may be expected to advance scientific understanding by isolating factors that limit predictability for episodes of western North Pacific TCs and associated downstream high-impact weather events over the eastern North Pacific and North America, establishing the relative levels of predictability for the large-scale flow regimes and regime transitions in which these episodes occur, and increasing understanding of the mechanisms that govern the predictive skill of high-impact weather events. The anticipated advances in scientific understanding may be expected to translate into improved forecasts of high-impact weather events over the eastern North Pacific and North America that are challenging to predict, thereby benefiting operational forecasting practice in the U.S.