The skill of a combined grand ensemble (GE), which is constructed from three operational global ensemble prediction systems (EPS), is evaluated with respect to the probability forecast of a tropical cyclone (TC) being within a specified area. Anisotropic probability ellipses are defined from the GE to contain 68% of the ensemble members. Forecast reliability is based on whether the forecast verifying position is within the ellipse. A sharpness parameter is based on the size of the GE-based probability ellipse relative to other operational forecast probability ellipses. For the 2010 Atlantic TC season, results indicate that the GE ellipses exhibit a high degree of reliability whereas the operational probability circle tends to be over-dispersive. Additionally, the GE ellipse tends to be sharper than the operational product for forecast intervals beyond 48 hours. The size and shape of the GE ellipses varied with TC track types, which suggests that information about the physics of the flow-dependent system is retained whereas isotropic probability ellipses may not reflect variability associated with track type. It is concluded that the GE probability ellipse demonstrates utility for combined EPS to enhance probabilistic forecasts for use as TC-related decision aids, as there is a potential for reducing the sizes of warning areas.

The thesis work was in two major parts: development and testing of a new approach to detecting and tracking tropical cyclones in climate models; and application of an extreme value statistical approach to enable assessment of changes in weather extremes from climate models. The tracking algorithm applied a creative phase-space approach to differentiate between modeled tropical cyclones and their mid-latitude cousins. A feature here was the careful attention to sensitivity to choice of selection parameters, which is considerable. The major finding was that the changes over time were relatively insensitive to these details. This new approach will improve and add confidence to future assessments of climate impacts on hurricanes. The extremes approach utilized the Generalized Pareto Distribution (one of the standard approaches to statistics of extremes) applied to present and future hurricane distributions as modeled by a regional climate model, then applied the changes to current observations to extract the changes in the extremes. Since climate models cannot resolve these extremes directly, this provides an excellent method of determining weather extremes in general. This is of considerable societal importance as we are most vulnerable to such extremes and knowledge of their changes enables improved planning and adaptation strategies.

The dynamics and predictability of various aspects of tropical cyclone track and intensity forecasting are explored through the use of real-time convection-permitting ensemble forecasts generated by a regional-scale model that employs advanced data assimilation techniques. Airborne Doppler radar observations, as well as sounding observations gathered during NASAs Hurricane and Severe Storm Sentinel (HS3) are assimilated and the resulting sensitivity and uncertainty of divergent track and intensity forecasts for three Atlantic tropical cyclones (TCs; Hurricane Sandy (2012), Hurricane Nadine (2012), and Hurricane Edouard (2014)) are explored. Ensemble members are separated into groups according to their performance and composite analyses and ensemble sensitivity techniques are employed to diagnose the sources of greatest sensitivity and uncertainty, as well as to dynamically explain the divergent behavior observed in the forecasts.The analysis of the Hurricane Sandy (2012) ensemble reveals that the divergent track forecasts result from differences in the location of Sandy that develop over the first 48-h of the simulation as a result of variance in the strength of the environmental winds that Sandy is embedded in throughout this period. Disparities in the strength and position of an approaching mid-latitude trough yield divergence in track forecasts of Hurricane Nadine (2012); an increased interaction between the mid-latitude system and the TC steers Nadine eastward, while a reduced interaction allows the TC to be steered westward ahead of the approaching trough. In addition, the inclusion of 6-h sea surface temperature (SST) updates considerably improves Nadines intensity forecasts, highlighting the importance of accurate SST fields when simulating TCs embedded in marginally favorable environmental conditions. Finally, considerable variance in the rapid intensification (RI) onset time in the Hurricane Edouard (2014) ensemble results from small distinctions in the magnitude of deep-layer shear prior to RI, which contributes to differences in the vortex tilt magnitude, the strength and location of the inner-core convection associated with the developing vortex, and the subsequent precession process.

This book deals with recent advances in our understanding and prediction of tropical cyclogenesis, intensification and movement as well as landfall processes like heavy rainfall, gale wind and storm surge based on the latest observational and numerical weather prediction (NWP) modeling platforms. It also includes tropical cyclone (TC) management issues like early warning systems, recent high impact TC events, disaster preparedness, assessment of risk and vulnerability including construction, archiving and retrieval of the best tracking and historical data sets, policy decision etc., in view of recent findings on climate change aspects and their impact on TC activity. The chapters are authored by leading experts, both from research and operational environments. This book is relevant to cyclone forecasters and researchers, managers, policy makers, graduate and undergraduate students. It intends to stimulate thinking and hence further research in the field of TCs and climate change, especially over the Indian Ocean region and provides high-quality reference materials for all the users mentioned above for the management of TCs over this region.

This book deals primarily with monitoring, prediction and understanding of Tropical Cyclones (TCs). It was envisioned to serve as a teaching and reference resource at universities and academic institutions for researchers and post-graduate students. It has been designed to provide a broad outlook on recent advances in observations, assimilation and modeling of TCs with detailed and advanced information on genesis, intensification, movement and storm surge prediction. Specifically, it focuses on (i) state-of-the-art observations for advancing TC research, (ii) advances in numerical weather prediction for TCs, (iii) advanced assimilation and vortex initialization techniques, (iv) ocean coupling, (v) current capabilities to predict TCs, and (vi) advanced research in physical and dynamical processes in TCs. The chapters in the book are authored by leading international experts from academic, research and operational environments. The book is also expected to stimulate critical thinking for cyclone forecasters and researchers, managers, policy makers, and graduate and post-graduate students to carry out future research in the field of TCs.