Tropical Cyclone

BACKGROUND

RAL’s Joint Numerical Testbed Program (JNTP) has a number of efforts related to tropical cyclone (TC) forecasting.  These will be described below as they relate to the JNTP’s  Developmental Testbed Center (DTC); the Tropical Cyclone Modeling Team (TCMT); the Tropical Cyclone Guidance Project (TCGP); and the Tropical Cyclone Data Project (TCDP).

The Developmental Testbed Center works closely with NCEP’s Environmental Modeling Center (EMC) to support the Hurricane Weather Research and Forecasting (HWRF) system to the research community. The team also tests new capabilities coming from the research community to determine their potential for improving the forecast skill of HWRF.  The goals of this work are to accelerate the improvement in TC forecasts by providing a mechanism for efficiently transitioning research into operations, and through extensive testing of new capabilities to determine their impacts on operational predictions. 

The focus of RAL’s Tropical Cyclone Modeling Team is testing and evaluation of experimental models for tropical cyclone forecasting. Currently, the primary sponsor of the TCMT is NOAA’s Hurricane Forecast Improvement Project (HFIP).  In coordination with the HFIP teams, the TCMT collects, evaluates, and provides results of tropical cyclone track forecasts to the broader HFIP community. Statistical approaches and new graphical displays are developed by the TCMT. Current efforts are focused on methods of evaluation for ensemble tropical cyclone forecasts of rapid intensity change and development of a specialized display and diagnostic evaluation system for use at the National Hurricane Center (NHC).

The TCGP provides real-time visualizations of TC track and intensity guidance through an outward-facing web page that receives millions of hits each year. TCGP also collects real-time tropical cyclone guidance data from numerical prediction centers around the world and collates these data into a publicly-available global repository of TC forecast aids. The site is widely used by forecasters, emergency managers, government agencies (e.g., NOAA, FEMA, DHS), private-sector firms (e.g., ship-routing, transportation and logistics, energy producers, energy and risk trading, media), weather enthusiasts, and the general public. The overarching goal of TCGP is to foster increased development of forecast aids for global basins by engaging the wider community of operational centers, academic researchers, and commercial interests, ultimately moving the community’s focus beyond track and intensity to a more expansive focus on TC structure.

The goal of TCDP is to provide and maintain a new historical database of TC wind structure parameters that is based on high quality observational sources such as high-resolution flight level data. This new database uses objective methods to optimally estimate the various database parameters, as well as to provide time-dependent error bounds on the estimated parameters. It is intended to provide the highest quality database possible for parametric wind modeling applications and model evaluation activities (e.g., verification), and to support basic and applied research on TC intensity and structure change.

FY2017 ACCOMPLISHMENTS

Developmental Testbed Center

Advancing HWRF physics

During FY2017, the DTC’s Hurricane team partnered with DTC Visitor Program Principal Investigators and subject area experts to help coordinate and test the performance of alternate physics schemes and innovations relative to the current parameterizations within the HWRF physics suite.  Physics advancements considered for testing covered radiation, planetary boundary layer (PBL), microphysics and cumulus parameterizations.  In addition to coordination and support for HWRF physics developers, the DTC evaluated the code readiness of candidate physics advancements and consulted with the EMC hurricane team on top priorities for HWRF 2017 pre-implementation testing.

Retrospective cases were run for four storms in the Atlantic (AL) basin (Edouard, Gonzalo, Matthew, Fiona) and two storms in the eastern North Pacific (EP) basin (Patricia, Dolores) that occurred during the 2014-2016 hurricane seasons. Four parallel experiments were run to test the sensitivity of three experimental physics configurations.  The control (CL) was run using the 2016 operational HWRF default settings.  Two RRTMG cloud-radiation experiments were conducted to test the sensitivity of an alternate cloud overlap (CO) methodology and the impact of a modified partial cloudiness scheme (PC).  Additionally, a cumulus parameterization replacement test (GF) was run to investigate the impact of the Grell-Freitas (GF) scheme compared to the operational scale-aware simplified Arakawa-Schubert (SAS).

The results of the pre-implementation testing were to adopt the PC innovations for the 2017 operational HWRF configuration.  The GF configuration continued to demonstrate promise with larger pre-implementation tests performed by EMC, however reproducibility issues when running with a different number of processors caused delays, resulting in a deferred decision on the GF configuration for the 2018 HWRF implementation.  Finally, inclusion of the CO innovation into HWRF was tabled until developers implement a namelist option for the new overlap method.  Further analysis of all three configurations are underway for inclusion in the project final report, which will be posted on the DTC website (http://www.dtcenter.org/eval/hwrf_GF_PC_CO/).  Additional cases are being added to increase the sample, particularly in the EP basin.  Furthermore, case studies focusing on particular storms are ongoing to better understand the behavior of each physics innovation.

Fig. 1. Probability density functions (PDFs) of the observed (yellow line) and model-simulated brightness temperatures for the GF (green), PC+CO (purple), CO (blue), PC (red), and CL (black) simulations at forecast hour 24 on d01 (left) and d03 (right).
Fig. 1. Probability density functions (PDFs) of the observed (yellow line) and model-simulated brightness temperatures for the GF (green), PC+CO (purple), CO (blue), PC (red), and CL (black) simulations at forecast hour 24 on d01 (left) and d03 (right).

A comparison of HWRF-simulated brightness temperatures (BT) with Geostationary Operational Environmental Satellite (GOES-13, channel 4) BTs is one approach the Hurricane team is pursuing to further analyze the experimental HWRF configurations.  Currently, Hurricane Matthew has been verified on the parent domain (d01) and innermost nest (d03).  In addition to the four aforementioned configurations, a supplemental test (PC+CO) was run to incorporate the combined impact of the PC and CO innovations.  Figure 1 demonstrates the different attributes of each configuration and domain, shown by probability density functions (PDFs) of the brightness temperature.  For the parent domain, the observed BT frequency increases steadily up to 280 K, followed by a sharp increase peaking at 290 K.  The GF and CO configurations peak at cooler temperatures, whereas the PC and PC+CO experiments demonstrate an improvement as they shift the PDF towards warmer BTs.  For the inner nest, the observational distribution is approximately uniform.  Conversely, the model-simulated BT PDFs are clearly bi-modal.  Notably, on both domains the model-simulated BTs all underestimate the observed frequency of BT from 235-275 K. 

Fig. 2: Examples of the NHC-Display tool showing the F-Deck editor (top panel), B-deck editor (middle panel), and wind radii display (bottom panel).
Fig. 2: Examples of the NHC-Display tool showing the F-Deck editor (top panel), B-deck editor (middle panel), and wind radii display (bottom panel).

Fractions skill score (FSS) was also computed to show the skill of each configuration (not shown).  Results indicate the GF configuration performs the best for all BT thresholds except the warmest (greater than 290 K) on the parent domain, whereas the PC configuration demonstrated the best skill on the inner-nest for BT thresholds greater than 250 K.  Notably, none of the configurations worsened HWRF’s ability to reproduce the observed BT PDF or substantially degraded the FSS relative to the CL. 

Tropical Cyclone Modeling Team

Development of a Tropical Cyclone Display and Diagnostic System

A next-generation display and diagnostic system is being developed to support evaluation needs of the U.S. National Hurricane Center (NHC) and the broader tropical cyclone (TC) research community.  The new hurricane display and diagnostic capabilities allow forecasters and research scientists to more deeply examine the performance of operational and experimental models.  The system is built upon modern and flexible technology, including OpenLayers Mapping tools that are platform independent. The forecast track and intensity along with associated observed track information are stored in an efficient MySQL database.  The system provides an easy-to-use interactive display system, and provides diagnostic tools to examine forecast track stratified by intensity.  Consensus forecasts can be computed and displayed interactively.  The system is designed to display observed (best track) and forecasted hurricane track information for both real-time and historical TC cyclones.  Display configurations are easily adaptable to meet the needs of the end-user preferences.

New technologies developed this year include a tool for editing the hurricane fix-position database (F-deck) and the best-track database (B-deck).  The F-deck editing tool allows NHC staff to add or edit the estimated location of hurricanes using fixed-position information from aircraft analysis, radar, satellite, microwave, and scatterometer observations.  This information is used to improve the location of the hurricane in the B-deck database during post-hurricane season analysis.  Other ongoing enhancements include improving capabilities for stratification and evaluation of historical best tracks, development and implementation of additional methods to stratify and compute consensus hurricane track and intensity forecasts, and the development of a wind radii display tool.  

Website: http://www.hfip.org/nhc-display

Ensemble Rapid Intensification Products

Fig 3. HWRF ensemble mean frequency distributions for the RI/RW bins during 0-24 (left), 24-48 (center), and 48-72 (right) time periods.
Fig 3. HWRF ensemble mean frequency distributions for the RI/RW bins during 0-24 (left), 24-48 (center), and 48-72 (right) time periods.

Building on last year’s HFIP Demo Rapid Intensification (RI) activities, the RI probability for all available model configurations were computed and displayed for each initialization time in 2017. Ensemble RI products were generated to show the ensemble frequency distributions of each model configuration for RI/RW (rapid weakening) during the three time periods (Figure 2) for a single initialization of Hurricane Jose.  

Ensemble RI products were generated and posted online for distribution to the community. Website: https://www.ral.ucar.edu/projects/hfip/d2017/ensRI/

Tropical Cyclone Guidance Project (TCGP)

New TCGP Data and Visualization

Fig 4. An example curve boxplot visualization for Hurricane Harvey, showing the median track (yellow), the central envelope (dark purple shading), the outer envelope (light purple shading), and the outlier tracks (blue).
Fig 4. An example curve boxplot visualization for Hurricane Harvey, showing the median track (yellow), the central envelope (dark purple shading), the outer envelope (light purple shading), and the outlier tracks (blue).

During FY2017, TCGP continued to provide reliable visualizations of the publicly available TC guidance product. Many companies and other sites rely on TCGP’s open data repository; web logs show on order of 15-25 GB of automatic data downloads per day. Through collaboration with Mahsa Mirzargar (University of Miami), a new visualization, called the curve boxplot, has been implemented in TCGP to analyze and visualize ensemble tracks. Analogous to the conventional boxplot, the curve boxplot provides the statistical summarization of an ensemble in terms of its main features: the most representative member (i.e., median), quantile information, and potential outliers. Figure 4 shows an example visualization of some early track forecasts from what the disturbance that eventually became Hurricane Harvey.

Tropical Cyclone Data Project (TCDP)

Research Use of TC Datasets of Aircraft and Satellite Observations

To support the goal of providing a new database of historical database of TC wind structure parameters, TCDP released three major source datasets to the public in FY2016. Each dataset is a high quality research-grade dataset of TC-focused wind data, from aircraft or satellite observations. The datasets use modern standards and formats, and serve as source data input for the new historical database. These include the:

  • Enhanced Vortex Data Message Dataset (VDM+, released 25 Nov 2015),
  • QuikSCAT Tropical Cyclone Radial Structure Dataset (QSCAT-R, released 23 Dec 2015), and
  • Extended Flight Level Dataset for Tropical Cyclones (FLIGHT+, released 20 April 2016).

Research use of these datasets has continued to increase. VDM+ now has 29 registered users and FLIGHT+ has 18 registered users. Many of the users are graduate students who are using the datasets in their thesis or doctoral research. By the end of FY2017, the VDM+ Dataset had been used in three published papers, a Ph.D. dissertation, and a Master’s thesis. The FLIGHT+ Dataset had been used in one Master’s thesis and three published papers.

FY2018 plans 

Developmental Testbed Center

For FY2018, the DTC will continue its work aimed at improving the HWRF physics through partnerships with physics developers. The performance of alternate physics schemes and innovations to the current parameterizations within the HWRF physics suite will be investigated. Retrospective forecasts using the most recent HWRF model version will be conducted to evaluate the performance of each innovation. Upgrades to the atmospheric component of HWRF will be passed to EMC to be included in its pre-implementation testing for the HWRF 2017 implementation.

Tropical Cyclone Modeling Team

For FY2018, the TCMT will continue to enhance graphical display diagnostic tools through additional stratifications and inclusion of gridded forecast, satellite, and sea surface temperature fields. New diagnostic tools that provide information on tropical cyclone wind radii structure and other diagnostic guidance requested by NHC.  Additionally, ensemble RI forecasts for the 2018 hurricane season will be evaluated and made available through the TCMT website.  The TCMT will also start evaluating other ensemble-based forecasts such as tropical cyclone genesis and spatial parameters.