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What’s New With The NHC Guidance Models and Products

What’s New With The NHC Guidance Models and Products. Bernard N. Meisner Science & Technology Services Division NWS Southern Region Fort Worth, Texas. The views expressed herein are those of the author and do not necessarily reflect the position of the National Weather Service.

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What’s New With The NHC Guidance Models and Products

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  1. What’s New With TheNHC Guidance Modelsand Products Bernard N. Meisner Science & Technology Services Division NWS Southern Region Fort Worth, Texas The views expressed herein are those of the author and do not necessarily reflect the position of the National Weather Service. June 2010

  2. What’s New 2010 Outline • Product changes. • Review of interpolated guidance models. • Performance of the track and intensity forecasts in recent years. • Review of track and intensity ensembles. • Logistic Growth Equation intensity forecast model.

  3. What’s New 2010 Outline • Annual adjustment to error cone width. • Change to Graphical Tropical Weather Outlook probabilities. • The Saffir-Simpson Hurricane Wind Scale. • New GOES-East Hurricane Rapid Scan Sector.

  4. What’s New 2010 Products • Watches now issued when tropical storm conditions are possible along the coast within 48 hours; warnings, within 36 hours. • The text Wind Speed Probability product for Gulf of Mexico will include a new location, corresponding to the Deepwater Horizon site. • Tropical cyclone forecast cone size will be updated. • Genesis forecasts will be provided to nearest 10%, instead of low/medium/high categories. • Saffir-Simpson Hurricane Wind Scale will no longer be tied to specific storm surge and flooding effects. http://www.nhc.noaa.gov/pdf/NHC_Product_Description_20100217.pdf

  5. What’s New 2010 GFSI, GFDI, HWFI, NGPI, UKMI, EMXI, CMCI,… Interpolated Guidance Models Refresher

  6. Interpolated Models • Output from the most recent run of the dynamic numerical models is not available to the hurricane specialists until after they have made their forecasts. • Forecast data from the previous run of the model is adjusted such that the six hour forecast exactly matches the observed position and intensity of the tropical cyclone. • For historic reasons, the adjusted versions of the models are called interpolated models.

  7. Interpolated Models 126 hr 102 hr 78 hr 120 hr Forecast from 0600 UTC model run 96 hr 54 hr 30 hr 6 hr 72 hr Forecast from 0600 UTC model run “interpolated” to 1200 UTC position 48 hr 24 hr 0 hr Storm location at 1200 UTC

  8. Recent Performance of Track Forecasts What’s New 2010

  9. 2009 Atlantic Season 2009 Atlantic Season 2009 Average 9 Storms 8 3 Hurricanes 5 2 Major 2

  10. 2009 Atlantic Season Grace Bill Most storms had well-behaved tracks

  11. 2009 Atlantic Verification VERIF TRACK INT TIME NUM (n mi) (kt) ============================ 000 144 9.6 1.6 012 120 30.1 6.4 024 9644.511.4 036 7561.814.9 048 6173.217.5 072 49119.220.6 096 38197.9 19.5 120 22292.316.6 Values in green meet or exceed all-time records. http://www.nhc.noaa.gov/verification/

  12. Track Forecast TrendsOfficial Forecasts, Atlantic Basin 72 h 120 h 96 h 48 h 24 h Errors reduced by 50% since 1990 http://www.nhc.noaa.gov/verification/

  13. Atlantic Track Errorsvs. Five -Year Mean Official forecast error was generally less than five year mean, even though the season was more challenging than recent years. CLIPER5 2009 2004-8 Official 2004-8 2009

  14. Track Forecast TrendsOfficial Forecasts, Atlantic Basin 48 h 72 h 24 h 96 h 120 h Skill has increased since the 1990’s,but had been relatively flat until the last two years. Sharp increase in last two years perhaps due to greater availability of the ECMWF. http://www.nhc.noaa.gov/verification/

  15. Track Forecast TrendsDynamic Models, 48 hr fcst. UKMET, NOGAPS consistently trail the other models. Over 2007-9, UKMET helped the TVCN consensus, while NOGAPS degraded it.

  16. Atlantic Basin2009 Track Summary • Official track forecasts set records for accuracy at 24-72 hours. Sharp increase in skill in last two years may be due to greater availability of the ECMWF. • Skill of the official forecasts was very close to that of the consensus models and the best performing of the dynamical models. • The GFS and ECMWF were the most skillful, and the GFDL also performed well. The NOGAPS and UKMET again performed poorly. • The FSSE was the best of the ensembles. • Corrected ensembles had less skill than the uncorrected ensembles.

  17. Track Ensembles What’s New 2010

  18. The Value of Ensembles • In strong flow regimes, errors in the initial conditions will dominate. Ensembles of the same model with varying initial conditionsare effective. • GFS ensemble (AEMI) has little hurricane track skill. • In weak flow regimes, model parameterization and physics will dominate the forecast. In these situations, ensembles using the same initial conditions and different models are effective. Stensrud, David J., et al., 1999: Using Ensembles for Short-Range Forecasting. Mon. Wea. Rev., Vol. 127, No. 4, pp. 433–446.

  19. Track Ensembles GUNA: GFDL, UKMET, NOGAPS & AVN (now GFS) TCON: Track CONsensus TVCN:TrackVariableCoNsensus TCCN: Track Bias Corrected CoNsensus TVCC: Track Variable Bias Corrected Consensus AEMI: Aviation Ensemble Mean Interpolated FSSE: Florida StateUniv. Super Ensemble WeatherPredict Consulting shares Superensemble™ hurricane forecasts with the National Hurricane Center, in support of NOAA’s public safety mission. National Weather Service

  20. Ensemble Model DefinitionsNames will henceforth remain the same,but individual members may change from year to year Track Ensembles *subjective quality control applied to UKMet automated storm tracker

  21. Bias-Corrected Ensembles Atlantic TCCN&TVCC Ensembles: The average north-south and east-west forecast errors from the previous Atlantic seasons are computed for each forecast lead time. These observed errors are subtracted from the TCON and TVCN ensembles to generate the bias-corrected TCCN and TVCC forecasts. National Weather Service

  22. Bias Correction Example Dolly 84 72 60 TVCN 48 36 24 TVCC Biased corrected 12

  23. Recent Performance of Intensity Forecasts What’s New 2010

  24. Consensus Model DefinitionsNames will remain the same,but models may change Intensity Ensembles Decay SHIPS, LGEM: Statistical Dynamic Models (Think MOS): GFDL, HWRF: Dynamic Numerical Models

  25. 2009 Atlantic Verification LGEM ICON FSSE Official HWRF Decay SHIPS GFDL

  26. Atlantic Intensity Errorsvs. Five -Year Mean Official forecast error was greater than five year mean, but the season was also more challenging than recent years. 2009 2004-8 2009 Decay- SHIFOR5 Official 2004-8

  27. Intensity Forecast TrendsOfficial Forecasts, Atlantic Basin 72 h 120 h 96 h 48 h 24 h One Saffir-Simpson Category The goals of the Hurricane Forecast Improvement Project are to improve intensity forecasts by 20% in five years; 50% in 10 years. http://www.nhc.noaa.gov/verification/

  28. Atlantic Basin2009 Intensity Summary • Intensity was more difficult to forecast in 20091. • Official intensity errors for the Atlantic basin in 2009 were mostly above the previous 5-yr means, but forecast skill was at or just above historical highs. • The Logistic Growth model (LGEM) performed best – its second year in a row as the top model. • The dynamical GFDL and Hurricane WRF models performed poorly – so poorly that the ICON 2 consensus was less accurate than the LGEM.1as measured by Decay-SHIFOR (climatology + persistence) 2 Four-model (DSHP/LGEM/HWRF/GFDL) statistical-dynamic consensus

  29. LGEM: Logistic GrowthEquation Model What’s New 2010

  30. Logistic Growth Model • The logistic equation was initially developed to model population growth. • The rate of intensification is proportional to the current intensity and the amount ofavailable resources. • The GFS model provides the forecast track and environmental parameters the storm is expected to encounter.

  31. Logistic Growth Model Maximum Possible Environment Most Favorable For Intensification Environment Somewhat Favorable For Intensification Initial Intensity Intensity Environment Somewhat Favorable For Dissipation Environment Most Favorable For Dissipation 0 Time

  32. Logistic Growth Model Statistical-Dynamic Predictor variables include: • Difference between current intensity and maximum possible intensity (from weekly SST analyses). • Vertical shear of the (850-200mb) horizontal wind.* • Persistence (intensity change in previous 12 hrs). • Average 200 mb temperature.* Warm air at upper-levels inhibits convection (thunderstorms). • Average 200 mb westerly wind component.* • Flux convergence of eddy angular momentum at 200mb.* Intensification begins from the top down. • Day of the year (Julian Day – 253 [Sept 10th]). * averaged along forecast track only over the 24 hours prior to the valid time

  33. Logistic Growth Model Statistical-Dynamic Differences from SHIPS*: • LGEM uses a logistic growth equation;SHIPS uses a regression equation. • LGEM should be better at predicting rapid intensification. • LGEM is more sensitive to track forecast errors. • LGEM is more sensitive to environmental changes at the end of the forecast period. • LGEM can better represent intensity changes of storms that move from water to land and then back over water.*Statistical Hurricane Intensity Prediction Scheme • The SHIPS satellite-derived parameters are currently not in the LGEM forecast.

  34. Adjustments to theWidth of the Error Cone What’s New 2010

  35. Adjusted Error Cone The Error Cone is formed by enclosing the area swept out by a set of circles along the forecast track (at 12, 24, 36, … 120 hours). Two-thirds of the official forecast errors over a five year sample fall within each circle. The same sized cone is used for all storms in the current season. http://www.nhc.noaa.gov/aboutcone.shtml

  36. Adjusted Error Cone Remember: There is a one in three chance a storm will track outside the Error Cone. http://www.nhc.noaa.gov/aboutcone.shtml

  37. Graphical Tropical Weather Outlook What’s New 2010

  38. Graphical TropicalWeather Outlook Categories were adjusted in 2009 to reflect verification from the 2008 hurricane season. Low genesis probability: less than 30% (formerly 20%) Medium genesis probability: 30-50% (formerly 20-50%) High genesis probability (over 50%) Instead of low/medium/high categories, genesis probabilities will now be provided to the nearest 10%. http://www.nhc.noaa.gov/aboutgtwo.shtml

  39. Graphical TropicalWeather Outlook

  40. Graphical TropicalWeather Outlook

  41. Graphical TropicalWeather Outlook

  42. Graphical TropicalWeather Outlook

  43. Genesis Forecast Verification Slight tendency to over-forecast formation General tendency to under-forecast formation

  44. What’s New 2010 All references to storm surge and flooding effects have been removed The Saffir-SimpsonHurricane Wind Scale

  45. The Saffir-Simpson Scale • In 1967, the United Nations commissioned Herb Saffirto study low-cost housing in regions of the world that were prone to tropical cyclones and hurricanes. • Saffir realized there was no way to describe the effects of a hurricane, so he developed his own five-category scale. • Robert Simpson, NHC Director, modified Saffir's work, adding lowest barometric pressures and • a range of storm surge heights for a given category. • In 1970, the National Hurricane Center started using the scale experimentally. It became operational in 1975. Hurricane Camille, 1969 http://news.nationalgeographic.com/news/2005/12/1220_051220_saffirsimpson.html

  46. Ike-Alicia Comparison Alicia (Cat 3) Ike (Cat 2)

  47. The Saffir-Simpson Wind ScaleOperational for 2010 In an effort to ensure storm surge forecasts are understood fully by the widest possible audience storm surge or storm tide will be expressed in terms of “height above ground level” or “inundation.” http://www.nhc.noaa.gov/aboutsshs.shtml

  48. What’s New 2010 New GOES-EastHurricane Rapid Scan Sector

  49. GOES-EastHurricane Rapid Scan Sector • Supports a major tropical research project. • Will provide up to four additional scans of the East and Central Tropical Atlantic per hour, in addition to the two standard scans. • Available August 1 - September 30. • Normal RSO requests to support NWS operations will take precedence over the research requests. http://www.ssd.noaa.gov/PS/SATS/GOES/EAST/sched.html

  50. For More Information… Upcoming VISIT Tropical Training Sessionshttp://rammb.cira.colostate.edu/visit/topic_tropical.html NHC Forecast Model Background & Informationhttp://www.nhc.noaa.gov/aboutmodels.shtml Tropical Cyclone Predictionwww.meted.ucar.edu/tropical/textbook/ch11/obs_anl_pred_11_5.html An Overview of NHC Prediction Modelswww.srh.noaa.gov/srh/ssd/nwpmodel/html/nhcmodel.htm Advances and Challenges at the NHCWea. Forecasting, 24, 395-419 (April 2009) Special thanks to James Franklin, Richard Pasch and the staff of the NWS NCEP’s Tropical Prediction Center for information and materials used in this presentation. Thanks also to Lance Wood, WFO Houston/Galveston.

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