Understanding the predictability of tropical cyclones from hours to weeks
Our field has established a solid foundation concerning the factors limiting our ability to predict the intensity and structure of high-impact tropical cyclones (TCs) on weather timescales (e.g., days). These factors include the challenge in predicting the rapid intensification of TCs under moderate vertical wind shear, the critical need for inner-core observations of TCs, and improved understanding of the air-sea fluxes that fuel intense TCs. While much work remains to realize the upper (intrinsic) limit of TC predictions on weather timescales, this will not be the primary focus of this seminar. Instead, the primary focus of this seminar is aimed at understanding the predictability of TCs on subseasonal time scales, a relatively new horizon. Considerable eGort is now being placed toward the goal of predicting high impact weather beyond the well-established, 2-week, limit of predictability. A crucial first step towards these eGorts is to first establish the intrinsic limit of subseasonal TC predictions. The global Model for Prediction Across Scales (MPAS) with 15 km uniform grid spacing is used to explore opportunities to predict TC activity out to 5 weeks. After understanding the MPAS TC climatology, a series of identical twin experiments are conducted to examine the intrinsic predictability of large-scale conditions relevant for TC activity and TC activity itself. It is shown that errors in weekly averaged fields relevant for TC activity, such as vertical wind shear and atmospheric moisture, have predictability slightly beyond the classic 2-week weather predictability limit and that weekly TC activity on the basin scale has an intrinsic limit of only 3 weeks.
