Using WindReductionFactors and GustFactors for Improved GFE Operations during Tropical Cyclones Jonathan Blaes and Reid Hawkins 16 November 2012

The Problem with Forecasting TC Winds and WindGusts Lack of science Lack of a consistent process Limited external consistency Limited collaboration Limited shift to shift forecast consistency Time/efficiency constraints

Development of Several GFE Tools The NC State CSTAR project has inspired the development of several GFE tools that are comprised of 4 types Quality Assurance tools  Ensure that the grids are consistent with the forecaster’s intent Existing Methodology tools  Provide specific values based on studies to derive the Wind and WindGust from gust factors or wind reductions Improved Methodology grids and tools (this talk)  Using WindReductionFactor and GustFactor grids Longer range, more sophisticated tools  Improved vortex in TCMWindTool, comprehensive dynamic tool These tools are still be developed and refined More significant testing is expected during the 2013 TC season

Improved Methodology Grids and Tools Utilizing the WindReductionFactor Grid WindReductionFactor grid – contains a rational (decimal) number over a fixed range that will be semi-persistent and collaborated. Forecasters run the TCMWindTool without any land reduction. A quick smooth of the TCMWindTool output is completed to remove the artifacts of the TCM quadrants. Next, they create the WindReductionFactor grids with the Assign_WindReductionFactor or WindReduction_Selector tool. Finally, the Wind_from_WindReductionFactor tool is used to create the Wind grids.

Creating Wind Grids via the WindReductionFactor Grid 1) Run the TCMWindTool with no land reduction

Creating Wind Grids via the WindReductionFactor Grid 2) Complete a quick smooth to remove TCM quadrant artifacts

Creating Wind Grids via the WindReductionFactor Grid 3) Edit the WindReductionFactor grid (lots of considerations need to be weighed here)

Creating Wind Grids via the WindReductionFactor Grid 4) Create the Wind grid via the Wind_from_WindReductionFactor tool

WindReductionFactor Grid Advantages Fairly Simple Adds some science to the process Forecasters can create the ReductionFactor grids ahead of time Allows forecasters to externally collaborate visually Results in improved shift to shift forecast continuity Should decrease workload Could utilize a climatological information Result in a much more appropriate Wind grid

WindReductionFactor Grid Disadvantages Need additional research and guidance (science) into how to draw reduction corridors. Climatology and prior work such as the Kaplan and DeMaria MEOW work could offer some help Another grid to edit in a difficult forecast situation An example of an idealized recommendation of the reduction factors for a TC that parallels the NC coast is shown here

Improved Methodology Grids and Tools Utilizing the WindGustFactor Grid WindGustFactor grid – contains a rational (decimal) number over a fixed range that will be semi-persistent and collaborated. First, forecasters create the Wind grids. Next, they create the WindGustFactor grids with the WindGustFactor_Selector tool Finally, the WindGust_from_WindGustFactor tool is used to create the WindGust grids.

Creating Wind Gust Grids via the WindGustFactor Grid 1) Edit the WindGustFactor grid via the WindGustFactor_Selector tool (variations options – CSTAR regression, mean, location specific values)

Creating Wind Gust Grids via the WindGustFactor Grid 2) Create the WindGust grid via the WindGust_from_WindGustFactor tool

WindGustFactor Grid Advantages Simple Introduces additional science and general constraints to the process Forecasters struggle with WindGusts. This methodology provides them some confidence that the gust have some objective reasoning. Forecasters can create the GustFactor grids ahead of time Allows forecasters to externally collaborate visually Results in improved shift to shift forecast continuity Should decrease workload Result in a much more appropriate Wind grid

WindGustFactor Grid Disadvantages Forecasters will still need to evaluate the mesoscale and boundary layer environment to account for circumstances such as CAD, enhanced mixing with drier air wrap around, boundary interaction, etc. Other GFE tools have shown promise using momentum transfer with NWP guidance to create wind gust grids, our methodology does not include this information Another grid to edit in a difficult forecast situation

WindReductionFactor and WindGustFactor Limitations Research dataset is limited Storms are from the Southeast only Most observations were on the left side of the TC No very strong Hurricanes Mesoscale variations will still be a struggle CAD, enhanced mixing with drier air wrap around, boundary interaction, etc. Background field issues Winds and WindGusts matching WWA products TCM product has lots of limitations

Experience During Hurricane Sandy This methodology or the associated tools were tested by some portion of the forecast staff at WFO ILM, RAH, and MHX during Hurricane Sandy. Initial feedback was positive. WFO ILM was on extreme edge of wind radii and had to edit the background wind field (increase winds west of I-95) RAH had a good experience with the TCWindGust tool During the event the WFO ILM ITO created a new tool “AssignWindReduction_Values“ to more easily assign WindReductionFactors

Next Steps Continue refinements to the tools Examine over water GF and incorporate into toolsExamine GF associated with Sandy in NJ/NY Develop training materials Explore some sort of verification Test the methodology at WFOs ILM, RAH, MHX, and MFL during the 2013 TC season

Acknowledgements Thanks to student volunteer Dan Brown for examining most of the gust factors and generating most of the charts as well. NC State student volunteers Rebecca Duell and Lindsey Anderson helped develop the overall methodology and completed the analysis of Hurricane Irene. Bryce Tyner and Dr Aiyyer Collaborative Investigator Reid Hawkins CSTAR TC Winds team GFE help from Carl Morgan (ILM) and Harry Gerapetritis (GSP)

Questions ? Josh Weiss, General Forecaster at WFO ILM, shown using some of the new GFE tools during Hurricane Sandy.

Extra Slides

CSTAR TC Wind Inspired Tools and Grids MaxWind tool MaxWindGust tool WindReduction tool WindReductionFactor grid Assign_WindReductionFactor WindReductionFactor_Selector tool Wind_from_WindReductionFactor tool TCWindGust tool WindGustFactor grid WindGustFactor_Selector tool WindGust_from_WindGustFactor tool

Comments from Pablo Santos, one of the original developers of the TCMWindTool 1) The biggest issues: This empirical approach assumes a smooth radial profile which has been found not to be the case always although I have to admit the Rankine Vortex does a decent job considering where it is starting from. Assumes smooth transition (interpolation) between forecast points that are provided only at 12 hour interval out to 48 hours and then at 24 hours interval out to day 5. Lots of potential errors from that alone. Does not account for inland decay, not even the 1995/2001 two parameters inland decay model from Mark DeMaria. Just a simple land friction coefficient. Does not account for elevations. Does not account for land/sea interface and offshore versus onshore fetch. This leaves it all to the forecaster to account for all of this by hand after running the tool which can be a daunting task. This to me is the greatest source of the discrepancies that you alluded to in the proposal. 2) The tool biggest strengths: It creates an official Wind Forecast that is consistent in track, magnitude and extent of wind radii with the official forecasts which are NHC's largest concerns. It has its own vortex interpolation algorithm in time that GFE simply cannot do.