|
|
- Current and potential use of ensemble forecasts in operational TC
forecasting: results from a global forecaster survey
Abstract: Publication date: September 2019Source: Tropical Cyclone Research and Review, Volume 8, Issue 3Author(s): H.A. Titley, M. Yamaguchi, L. Magnusson In order to understand the current and potential use of ensemble forecasts in operational tropical cyclone (TC) forecasting, a questionnaire on the use of dynamic ensembles was conducted at operational TC forecast centers across the world, in association with the World Meteorological Organisation (WMO) High-Impact Weather Project (HIWeather). The results of the survey are presented, and show that ensemble forecasts are used by nearly all respondents, particularly in TC track and genesis forecasting, with several examples of where ensemble forecasts have been pulled through successfully into the operational TC forecasting process. There is still, however, a notable difference between the high proportion of operational TC forecasters who use and value ensemble forecast information, and the slower pull-through into operational forecast warnings and products of the probabilistic guidance and uncertainty information that ensembles can provide. Those areas of research and development that would help TC forecasters to make increased use of ensemble forecast information in the future include improved access to ensemble forecast data, verification and visualizations, the development of hazard and impact-based products, an improvement in the skill of the ensembles (particularly for intensity and structure), and improved guidance on how to use ensembles and optimally combine forecasts from all available models. A change in operational working practices towards using probabilistic information, and providing and communicating dynamic uncertainty information in operational forecasts and warnings, is also recommended.
- Tropical Cyclone Prediction on Subseasonal Time-Scales
Abstract: Publication date: September 2019Source: Tropical Cyclone Research and Review, Volume 8, Issue 3Author(s): Suzana J. Camargo, Joanne Camp, Russell L. Elsberry, Paul A. Gregory, Philip J. Klotzbach, Carl J. Schreck, Adam H. Sobel, Michael J. Ventrice, Frédéric Vitart, Zhuo Wang, Matthew C. Wheeler, Munehiko Yamaguchi, Ruifen Zhan Here we discuss recent progress in understanding tropical cyclone (TC) subseasonal variability and its prediction. There has been a concerted effort to understand the sources of predictability at subseasonal time-scales, and this effort has continued to make progress in recent years. Besides the Madden-Julian Oscillation (MJO), other modes of variability affect TCs at these time-scales, in particular various equatorial waves. Additionally, TC activity is also modulated by extratropical processes via Rossby wave breaking.There has also been progress in the ability of models to simulate the MJO and its modulation of TC activity. Community efforts have created multi-model ensemble datasets, which have made it possible to evaluate the forecast skill of the MJO and TCs on subseasonal time-scales in multiple forecasting systems. While there is positive skill in some cases, there is strong dependence on the ensemble system considered, the basin examined, and whether the storms have extratropical influences or not. Furthermore, the definition of skill differs among studies. Forecasting centers are currently issuing subseasonal TC forecasts using various techniques (statistical, statistical-dynamical and dynamical). There is also a strong interest in the private sector for forecasts with 3-4 weeks lead time.
- Advances in understanding difficult cases of tropical cyclone track
forecasts
Abstract: Publication date: September 2019Source: Tropical Cyclone Research and Review, Volume 8, Issue 3Author(s): Linus Magnusson, James D. Doyle, William A. Komaromi, Ryan D. Torn, Chi Kit Tang, Johnny.C.L. Chan, Munehiko Yamaguchi, Fuqing Zhang Although tropical cyclone track forecast errors have substantially decreased in recent decades, there are still cases each season with large uncertainties in the forecasts and/or very large track errors. As such cases are challenging for forecasters, it is important to understand the mechanisms behind the low predictability. For this purpose the research community has developed a number of tools. These tools include ensemble and adjoint sensitivity models, ensemble perturbation experiments and nudging experiments. In this report we discuss definitions of difficult cases for tropical cyclone track forecasts, diagnostic techniques to understand sources of errors, lessons learnt in recent years and recommendations for future work.
- The Interaction Of Hurricane Michael With An Upper Trough Leading To
Intensification Right Up To Landfall
Abstract: Publication date: June 2019Source: Tropical Cyclone Research and Review, Volume 8, Issue 2Author(s): Jeff Callaghan Hurricane Michael was intensifying as it made landfall devastating areas of the Florida Panhandle including the small town of Mexico Beach. The structure of the hurricane is examined using radar wind data made available from aircraft reconnaissance missions. This showed a dominant warm air advection configuration (winds turning in direction in an anticyclonic fashion with height) around the core of the hurricane. Conventional radiosonde data was also used to study the warm air advection environment east of a deep layered tough system which Michael moved into and which appeared to favour such strong intensification. The structure of this deep trough is also examined and compared with a situation where Hurricane Dennis in 2005 weakened as it approached the coast in much the same region. It appears that the thermal structure of the upper trough at low to middle levels is critical to whether the hurricane intensifies or weakens with the presence of strong cold air advection associated with weakening.
- Overview on the progress of Working Group on Meteorology of ESCAP/WMO
Typhoon Committee in the recent 10 years
Abstract: Publication date: June 2019Source: Tropical Cyclone Research and Review, Volume 8, Issue 2Author(s): Xiaotu Lei, Clarence Fong, Vicente B. Malano, Che Gayah Ismail This paper reviews the major achievements of the Working Group on Meteorology (WGM) of ESCAP/WMO Typhoon Committee since its establishment in 2004, especially in tropical cyclone observational research and scientific experiments, tropical cyclone monitoring and forecasting technologies, seasonal prediction and climate change assessment for the past decade. The progress illustrates the great value of the Committee and WGM in monitoring and forecasting of tropical cyclones in the region and the improvement of disaster prevention and reduction capabilities.
- Role of Sea Surface Temperature in Modulating Life Cycle of Tropical
Cyclones over Bay of Bengal
Abstract: Publication date: June 2019Source: Tropical Cyclone Research and Review, Volume 8, Issue 2Author(s): Shyama Mohanty, Raghu Nadimpalli, Krishna K. Osuri, Sujata Pattanayak, U.C. Mohanty, Sourav Sil Sea surface temperature (SST) varies significantly in the presence of tropical cyclones (TCs). Using fixed SST throughout the integration of high resolution TC models is general practice in research and operational endeavor over the North Indian Ocean. The present study is to assess the impact of updating realistic SST in TC lifetime on track, intensity and rainfall of TCs. The Hurricane Weather Research Forecast (HWRF) model of single domain with 9km resolution is used. A total of 31 forecast cases are considered from 6 TCs during 2007- 16 with unique track and intensity characteristics. A set of two numerical experiments are done without (CNTL) and with 6-hourly SST update (SST) in TC lifetime.Mean track and intensity errors show that there is an improvement of 3–41% in track during 12–120h forecast length for SST run. The SST runs improve landfall position and time prediction by 20% and 33% respectively. The cross track error of SST run is comparable (44km) with average errors available for this basin (34km); and along track errors are improved by 60% as compared to CNTL as well as average errors of the basin. The model is biased to overestimate a weaker TC and underestimate a stronger TC, however, the bias is reduced in SST run by 5–51%. The analyses of wind, enthalpy flux and warm core structures provide insight for realistic intensity prediction of SST run unlike CNTL. Rainfall intensity and radial distribution is also improved in SST run. Thus, this study highlights the significance of ocean coupling with TC models to advance forecast guidance.
- Idealized Simulations of the Inner Core Boundary Layer Structure in a
Landfalling Tropical Cyclone. Part I: Kinematic Structure
Abstract: Publication date: June 2019Source: Tropical Cyclone Research and Review, Volume 8, Issue 2Author(s): Gabriel J. Williams The effects of coastal topography and coastal location in the distribution of boundary layer winds in the inner core of mature tropical cyclones are examined using a high-resolution multi-level model. In these numerical simulations, the evolution of the tropical cyclone boundary layer (TCBL) is studied in storm-relative coordinates, and in lieu of an actual steering current moving the model vortex, the position of the land-sea interface was shifted through the grid domain at a constant speed with separate surface boundary conditions specified over the land and ocean areas. It is shown that the presence of a coastal boundary produces land-induced asymmetries (along with an internal boundary layer) due to the asymmetric structure of surface drag. This land-induced asymmetry is found in both the azimuthal and radial wind field at landfall. For a moving storm, nonlinear advective interactions between storm-induced asymmetries and land-induced asymmetries can generate a lowlevel vorticity band ahead of the hurricane. When the storm motion vector has a component that is perpendicular to the coastal boundary, the interaction between this band and the mean vortex leads to a temporary weakening and re-intensification cycle. Furthermore, it is shown that the relative magnitude of the land-induced asymmetry depends upon the terrain slope and the terrain height such that the land-induced asymmetry dominates over the motion-induced asymmetry for elevated terrain. These results underscore the specific differences in boundary layer evolution and intensity evolution for hurricanes interacting with complex topographical features.
|
Open Access journal
