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

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

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

National Weather Service What’s New 2010 Watches now issued when tropical storm conditions are possible along the coast within 48 hours; warnings, within 36 hours.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.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.Tropical cyclone forecast cone size will be updated. Genesis forecasts will be provided to nearest 10%, instead of low/medium/high categories.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.Saffir-Simpson Hurricane Wind Scale will no longer be tied to specific storm surge and flooding effects. Products

National Weather Service Interpolated Guidance Models Refresher GFSI, GFDI, HWFI, NGPI, UKMI, EMXI, CMCI,… What’s New 2010

National Weather Service 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. 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. 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. For historic reasons, the adjusted versions of the models are called interpolated models.

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

National Weather Service Recent Performance of Track Forecasts What’s New 2010

National Weather Service 2009 Atlantic Season 2009 Average 9 Storms 8 3 Hurricanes 5 2 Major 2

National Weather Service 2009 Atlantic Season Most storms had well-behaved tracks Grace Bill

National Weather Service VERIF TRACK INT TIME NUM (n mi) (kt) ============================ Atlantic Verification Values in green meet or exceed all-time records.

National Weather Service Errors reduced by 50% since h 96 h 48 h 24 h 72 h Track Forecast Trends Official Forecasts, Atlantic Basin

National Weather Service Atlantic Track Errors vs. Five -Year Mean Official forecast error was generally less than five year mean, even though the season was more challenging than recent years. CLIPER5 Official

National Weather Service Track Forecast Trends Official Forecasts, Atlantic Basin 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. 120 h 96 h 72 h 48 h 24 h

National Weather Service Track Forecast Trends Dynamic Models, 48 hr fcst. UKMET, NOGAPS consistently trail the other models. Over , UKMET helped the TVCN consensus, while NOGAPS degraded it.

National Weather Service Atlantic Basin 2009 Track Summary Official track forecasts set records for accuracy at hours. Sharp increase in skill in last two years may be due to greater availability of the ECMWF.Official track forecasts set records for accuracy at 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.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 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.The FSSE was the best of the ensembles. Corrected ensembles had less skill than the uncorrected ensembles.Corrected ensembles had less skill than the uncorrected ensembles.

National Weather Service Track Ensembles What’s New 2010

National Weather Service The Value of Ensembles In strong flow regimes, errors in the initial conditions will dominate. Ensembles of the same model with varying initial conditions are effective. In strong flow regimes, errors in the initial conditions will dominate. Ensembles of the same model with varying initial conditions are effective. GFS ensemble (AEMI) has little hurricane track skill. 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. 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.

National Weather Service Track Ensembles GUNA:G FDL, U KMET, N OGAPS & A VN (now GFS) TCON:T rack CON sensus TVCN:T rack V ariable C o N sensus TCCN:T rack Bias C orrected C o N sensus TVCC: T rack V ariable Bias C orrected C onsensus AEMI:A viation E nsemble M ean I nterpolated FSSE:F lorida S tate Univ. S uper E nsemble National Weather Service WeatherPredict Consulting shares Superensemble™ hurricane forecasts with the National Hurricane Center, in support of NOAA’s public safety mission.

National Weather Service NameTypeMembers TCON Fixed Guidance from all models must be available GFDL, UKMet*, NOGAPS, GFS, Hurricane WRF (GUNA with HWRF) TVCN Variable Guidance from two or more models must be available GFDL, UKMet*, NOGAPS, GFS, Hurricane WRF, Navy GFDL, ECMWF (replaces CONU) TCCN Fixed – bias corrected Historic east-west and north-south errors removed – Atlantic forecast errors removed in Pacific GFDL, UKMet*, NOGAPS, GFS, Hurricane WRF (CGUN with HWRF) TVCC Variable – bias corrected Historic east-west and north-south errors removed – Atlantic forecast errors removed in Pacific GFDL, UKMet*, NOGAPS, GFS, Hurricane WRF, Navy GFDL, ECMWF (replaces CCON) Ensemble Model Definitions Names 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

National Weather Service 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. 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. These observed errors are subtracted from the TCON and TVCN ensembles to generate the bias-corrected TCCN and TVCC forecasts. National Weather Service

Bias Correction Example TVCN TVCC Biased corrected Dolly

National Weather Service Recent Performance of Intensity Forecasts What’s New 2010

National Weather Service Consensus Model Definitions Names will remain the same, but models may change NameTypeMembers ICON Fixed Guidance from all models must be available Decay SHIPS, GFDL, Logistic Growth Equation Model, Hurricane WRF IVCN Variable Guidance from two or more models must be available Decay SHIPS, GFDL, Logistic Growth Equation Model, Hurricane WRF, NAVY GFDL Intensity Ensembles Decay SHIPS, LGEM: Statistical Dynamic Models (Think MOS): GFDL, HWRF: Dynamic Numerical Models

National Weather Service 2009 Atlantic Verification LGEM HWRF GFDL Decay SHIPS FSSE Official ICON

National Weather Service Atlantic Intensity Errors vs. Five -Year Mean Official Official forecast error was greater than five year mean, but the season was also more challenging than recent years. Decay- SHIFOR

National Weather Service Intensity Forecast Trends Official Forecasts, Atlantic Basin The goals of the Hurricane Forecast Improvement Project are to improve intensity forecasts by 20% in five years; 50% in 10 years. One Saffir-Simpson Category 120 h 96 h 48 h 24 h 72 h

National Weather Service Atlantic Basin 2009 Intensity Summary Intensity was more difficult to forecast in Intensity was more difficult to forecast in 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.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 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. 1 as measured by Decay-SHIFOR (climatology + persistence)The dynamical GFDL and Hurricane WRF models performed poorly – so poorly that the ICON 2 consensus was less accurate than the LGEM. 1 as measured by Decay-SHIFOR (climatology + persistence) 2 Four-model (DSHP/LGEM/HWRF/GFDL) statistical-dynamic consensus

National Weather Service LGEM: Logistic Growth Equation Model What’s New 2010

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

National Weather Service Logistic Growth Model 0 Maximum Possible Intensity Time Environment Most Favorable For Intensification Environment Somewhat Favorable For Intensification Environment Somewhat Favorable For Dissipation Environment Most Favorable For Dissipation Initial Intensity

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

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

National Weather Service Adjustments to the Width of the Error Cone What’s New 2010

National Weather Service 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). 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. 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. The same sized cone is used for all storms in the current season.

National Weather Service Adjusted Error Cone Lead Time Radius (2007) Radius (2008) Radius (2009) 12 hours 39 n.mi. 36 n.mi Remember: There is a one in three chance a storm will track outside the Error Cone.

National Weather Service Graphical Tropical Weather Outlook What’s New 2010

National Weather Service Graphical Tropical Weather Outlook Categories were adjusted in 2009 to reflect verification from the 2008 hurricane season. Low genesis probability: less than 30% (formerly 20%) 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%. Instead of low/medium/high categories, genesis probabilities will now be provided to the nearest 10%.

National Weather Service Graphical Tropical Weather Outlook

National Weather Service Graphical Tropical Weather Outlook

National Weather Service Graphical Tropical Weather Outlook

National Weather Service Graphical Tropical Weather Outlook

National Weather Service Genesis Forecast Verification Slight tendency to over-forecast formation General tendency to under-forecast formation

National Weather Service The Saffir-Simpson Hurricane Wind Scale All references to storm surge and flooding effects have been removed What’s New 2010

National Weather Service The Saffir-Simpson Scale In 1967, the United Nations commissioned Herb Saffir to study low-cost housing in regions of the world that were prone to tropical cyclones and hurricanes. In 1967, the United Nations commissioned Herb Saffir to 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. 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 Robert Simpson, NHC Director, modified Saffir's work, adding lowest barometric pressures and a range of storm surge heights for a given category. 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 In 1970, the National Hurricane Center started using the scale experimentally. It became operational in Hurricane Camille, 1969

National Weather Service Ike-Alicia Comparison Ike (Cat 2)Alicia (Cat 3)

National Weather Service Category Wind (mph) Qualitative damage estimate Minimum Surface Pressure (mb) Storm surge (ft) One74-95Some> Two96-110Widespread Three Extensive Four Devastating Five>155Catastrophic< The Saffir-Simpson Wind Scale Operational 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.”

National Weather Service New GOES-East Hurricane Rapid Scan Sector What’s New 2010

National Weather Service GOES-East Hurricane Rapid Scan Sector Supports a major tropical research project. 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. 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. Available August 1 - September 30. Normal RSO requests to support NWS operations will take precedence over the research requests. Normal RSO requests to support NWS operations will take precedence over the research requests.

National Weather Service For More Information… Upcoming VISIT Tropical Training Sessions NHC Forecast Model Background & Information Tropical Cyclone Prediction An Overview of NHC Prediction Models Advances and Challenges at the NHC Wea. Forecasting, 24, (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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