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Tropical Cyclone Decay Over Land Study Update

This conference call on March 14, 2012, covers the decay of tropical cyclones over land, with a focus on data sets, storm analysis, modeling work, and future plans. Learn about wind speed reduction after landfall and implications for forecasting. Join the discussion and training materials for Weather Forecast Offices (WFOs). For more information, join us on the next call on Wednesday, April 11th at 11 a.m.

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Tropical Cyclone Decay Over Land Study Update

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  1. Conference CallMarch 14, 2012 • Decay over land • Update on modeling work • Training material for WFOs • Open discussion

  2. Decay over Land Goals: • Show how the wind speeds of “typical” landfalling tropical cyclones decay once over land • Show how wind speeds compare to NHC guidance

  3. Decay over Land Data set to use: • ASOS station observations frequently go missing (see JB’s blog posting) • HWIND analyses often not available once storm is over land • RUC analyses chosen • Available from NCDC since 2002 (data not online for 2006-2007—looking into this now)

  4. Decay over Land • Only storms that actually made landfall used in study • Only times the storm is over land used in analysis • Storm list: • Gabrielle (2007) -Irene (2011) • Kyle (2002) -Gaston (2004) • Isabel (2003) -Hanna (2008) • Charley (2004) -Ernesto (2006) • TD7 (2003)

  5. Decay over Land—Strong StormsIsabel (2003) & Irene (2011) Isabel (2003) Irene (2011)

  6. Decay over Land—Weaker Storms Kyle (2002) Gaston (2004)

  7. Decay over Land • Strong storms show sharp reduction in wind over first 6-24 hours once over land; little change afterwards • Timing of sharpest decrease in winds depends on angle with respect to coastline • Weaker storms show little reduction once over land • Sometimes, outer radii actually have slightly higher winds than closer to storm

  8. Land Decay Discussion • Land decay and climatology: other data sets to you besides RUC? NARR? CFSR? • Land decay and climatology: radii to use? • Reduction vs. max. wind forecast for various radii: calculate ratio of RUC analyzed winds at various radii and compare to forecast at each time?

  9. Modeling Update

  10. Landfall Verification: Run 4 SIMULATED LANDFALL TIME: 08/27/1500 UTC LANDFALL CENTRAL SLP: 961 hPa BEST TRACK LANDFALL TIME: 08/27/1200 UTC LANDFALL CENTRAL SLP: 952 hPa

  11. Run #7 • RTG SST data updated every 6 hours • Initialized 8/27/00 UTC (12 hours prior to landfall) • 9 km / 3 km nested run

  12. Best Track vs. Run #7 Track Irene 5 (SST updated, 8/25/12z initialization) Irene 7 (SST updated, 8/27/00z initialization)

  13. HWIND ANALYSIS, 8/27/1330 UTC ANALYZED MAX WIND: 80 KTS OBSERVED MAX WIND: 75 KTS Model Run 7, 8/27/1300 UTC MODELED MAX WIND: 70.3 KTS

  14. Radar Loop: Run 7

  15. Landfall Verification: Run 7 SIMULATED LANDFALL TIME: 08/27/1300 UTC LANDFALL CENTRAL SLP: 959 hPa BEST TRACK LANDFALL TIME: 08/27/1200 UTC LANDFALL CENTRAL SLP: 952 hPa

  16. Current/Future Modeling Work • Zhu et. Al (2008): WRF-LES simulation for Ivan (2004) • Provides guidance for initial WRF-LES simulation/namelist.input parameters • 5 domains, two-way nested: 8.1 km, 2.7 km, .9 km, .3 km, and .1 km grid spacing • Compare buoy/ASOS data to innermost domain

  17. Training Slides Outline (Gail Hartfield) • Slide 1: Overview of project purpose and plans • Slide 2: Basics of study: data/models used (could be combined with Slide 1) • Slide 3: Results of observed wind analyses (Irene) • Slide 4: NDFD verification summary (Irene)

  18. Training Slides Outline (Gail Hartfield) • Slide 5: Summary of modeling results • Slide 6: Potential TCWindTool improvements & Mike Brennan notes on TCM limitations • Slide 7: Guidance for WFOs on speed reduction and gusts in TCs • Slide 8: Future plans: Wind reduction & gust factors based on distance from center, topography, distance inland, etc.

  19. Open Discussion • Training slides discussion • Other topics? • Next call date: Wednesday, April 11th at 11 a.m.

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