national weather service what’s new with the nhc guidance models and products the views expressed...

National Weather Service

What’s New With TheWhat’s New With TheNHC Guidance ModelsNHC Guidance Models

and Productsand 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. MeisnerScience & Technology Services DivisionNWS Southern RegionFort Worth, Texas


What’s New 2010What’s New 2010

• Product changes.Product changes.

• Review of interpolated guidance models.Review of interpolated guidance models.

• Performance of the track and intensity Performance of the track and intensity forecasts in recent years.forecasts in recent years.

• Review of track and intensity ensembles.Review of track and intensity ensembles.

• Logistic Growth Equation intensity forecast Logistic Growth Equation intensity forecast model.model.

Outline



• Annual adjustment to error cone width.Annual adjustment to error cone width.

• Change to Graphical Tropical Weather Change to Graphical Tropical Weather Outlook probabilities.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



• Watches now issued when tropical storm conditions Watches now issued when tropical storm conditions are possible along the coast within 48 hours; are possible along the coast within 48 hours; warnings, within 36 hours.warnings, within 36 hours.

• The text Wind Speed Probability product for Gulf of The text Wind Speed Probability product for Gulf of Mexico will include a new location, corresponding to Mexico will include a new location, corresponding to the Deepwater Horizon site.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%, Genesis forecasts will be provided to nearest 10%, instead of low/medium/high categories.instead of low/medium/high categories.

• Saffir-Simpson Hurricane Wind Scale will no longer Saffir-Simpson Hurricane Wind Scale will no longer be tied to specific storm surge and flooding effects. be tied to specific storm surge and flooding effects.

Products

http://www.nhc.noaa.gov/pdf/NHC_Product_Description_20100217.pdf


Interpolated Guidance Interpolated Guidance Models RefresherModels Refresher

GFSI, GFDI, HWFI, NGPI, UKMI, EMXI, CMCI,…GFSI, GFDI, HWFI, NGPI, UKMI, EMXI, CMCI,…



Interpolated ModelsInterpolated Models

• Output from the most recent run of the dynamic Output from the most recent run of the dynamic numerical models is not available to the hurricane numerical models is not available to the hurricane specialists until after they have made their forecasts.specialists until after they have made their forecasts.

• Forecast data from the previous run of the model is Forecast data from the previous run of the model is adjusted such that the six hour forecast exactly adjusted such that the six hour forecast exactly matches the observed position and intensity of the matches the observed position and intensity of the tropical cyclone.tropical cyclone.

• For historic reasons, the adjusted versions of the For historic reasons, the adjusted versions of the models are called models are called interpolated modelsinterpolated models..


24 hr48 hr

72 hr

96 hr120 hr

0 hr

Forecast from0600 UTCmodel run

Forecast from 0600 UTCmodel run “interpolated”

to 1200 UTC position

30 hr

126 hr

54 hr

78 hr

102 hr

6 hr

Interpolated ModelsInterpolated Models

Storm locationat 1200 UTC


Recent Performance of Recent Performance of Track ForecastsTrack Forecasts



2009 Atlantic Season2009 Atlantic Season2009 Atlantic Season2009 Atlantic Season

2009 Average 9 Storms 8 3 Hurricanes 5 2 Major 2


2009 Atlantic Season2009 Atlantic Season

Most storms hadMost storms hadwell-behaved trackswell-behaved tracks

Grace

Bill


VERIF TRACK INTVERIF TRACK INT

TIME NUM (n mi) (kt)TIME NUM (n mi) (kt)

============================ ============================

000 144 9.6 1.6012 120 30.1 6.4024 96 44.5 11.4036 75 61.8 14.9048 61 73.2 17.5072 49 119.2 20.6096 38 197.9 19.5120 22 292.3 16.6

2009 Atlantic Verification2009 Atlantic Verification

Values in green meet or Values in green meet or exceed all-time records.exceed all-time records.

http://www.nhc.noaa.gov/verification/


Errors reduced by 50% since 1990

120 h

96 h48 h

24 h

72 h

Track Forecast TrendsTrack Forecast TrendsOfficial Forecasts, Atlantic BasinOfficial Forecasts, Atlantic Basin



Atlantic Track ErrorsAtlantic Track Errorsvs. Five -Year Meanvs. 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

2009

2004-8

2004-8

2009


Track Forecast TrendsTrack Forecast TrendsOfficial Forecasts, Atlantic BasinOfficial 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



Track Forecast TrendsTrack Forecast TrendsDynamic Models, 48 hr fcst.Dynamic Models, 48 hr fcst.

UKMET, NOGAPS consistently trail the other models. Over 2007-9, UKMET helped the TVCN consensus, while

NOGAPS degraded it.


Atlantic BasinAtlantic Basin2009 Track Summary2009 Track Summary

• Official track forecastsOfficial track forecasts set records for accuracy at 24-72 set records for accuracy at 24-72 hours. hours. Sharp increase in skill in last two years may be Sharp increase in skill in last two years may be due to greater availability of the ECMWF.due to greater availability of the ECMWF.

• Skill of the official forecasts was very close to that of the Skill of the official forecasts was very close to that of the consensus models consensus models and the best performing of the and the best performing of the dynamical models.dynamical models.

• The The GFS and ECMWF were the most skillfulGFS and ECMWF were the most skillful, and the , and the GFDL also performed well. The NOGAPS and UKMET GFDL also performed well. The NOGAPS and UKMET again performed poorly.again performed poorly.

• The FSSE was the The FSSE was the best of the ensemblesbest of the ensembles..

• Corrected ensembles had less skill Corrected ensembles had less skill than the uncorrected than the uncorrected ensembles.ensembles.


Track EnsemblesTrack Ensembles



The Value of EnsemblesThe Value of Ensembles

• In In strong flow regimesstrong flow regimes, errors in the initial , errors in the initial conditions will dominate. Ensembles of the conditions will dominate. Ensembles of the same modelsame model with varying initial conditions with varying initial conditions are are effective. effective.

• GFS ensemble (AEMI) has little hurricane track skill.GFS ensemble (AEMI) has little hurricane track skill.

• In In weak flow regimesweak flow regimes, model parameterization , model parameterization and physics will dominate the forecast. In these and physics will dominate the forecast. In these situations, ensembles using the same initial situations, ensembles using the same initial conditions and conditions and different modelsdifferent models are effective. are effective.Stensrud, David J., et al., 1999: Stensrud, David J., et al., 1999: Using Ensembles for Short-Range Using Ensembles for Short-Range Forecasting.Forecasting. Mon. Wea. Rev., Vol. 127, No. 4, pp. 433–446. Mon. Wea. Rev., Vol. 127, No. 4, pp. 433–446.


Track EnsemblesTrack Ensembles

GUNA:GUNA: GGFDL, FDL, UUKMET, KMET, NNOGAPS & OGAPS & AAVN (now GFS)VN (now GFS)

TCON:TCON: TTrack rack CONCONsensussensus

TVCN:TVCN: TTrackrack VVariableariable CCooNNsensussensus

TCCN:TCCN: TTrack Bias rack Bias CCorrected orrected CCooNNsensussensus

TVCC: TVCC: TTrack rack VVariable Bias ariable Bias CCorrected orrected CConsensusonsensus

AEMI:AEMI: AAviation viation EEnsemblensemble M Meanean I Interpolatednterpolated

FSSE:FSSE: FFlorida lorida SStatetate Univ.Univ. S Super uper EEnsemblensemble


WeatherPredict Consulting shares Superensemble™ hurricane forecasts with the National Hurricane Center, in support of NOAA’s public safety mission.


Name Type Members

TCONFixedGuidance from all models must be available

GFDL, UKMet*, NOGAPS, GFS,Hurricane WRF(GUNA with HWRF)

TVCNVariableGuidance from two or more models must be available

GFDL, UKMet*, NOGAPS, GFS,Hurricane WRF, Navy GFDL, ECMWF (replaces CONU)

TCCNFixed – bias correctedHistoric east-west and north-south errors removed – Atlanticforecast errors removed in Pacific

GFDL, UKMet*, NOGAPS, GFS, Hurricane WRF(CGUN with HWRF)

TVCCVariable – bias correctedHistoric east-west and north-south errors removed – Atlanticforecast errors removed in Pacific

GFDL, UKMet*, NOGAPS, GFS,Hurricane WRF, Navy GFDL, ECMWF (replaces CCON)

Ensemble Model DefinitionsEnsemble Model DefinitionsNames will henceforth remain the same,Names will henceforth remain the same,

but individual members may change from year to yearbut individual members may change from year to year

Track Ensembles

*subjective quality control applied to UKMet automated storm tracker


Bias-Corrected EnsemblesBias-Corrected Ensembles

Atlantic Atlantic TCCN TCCN && TVCC TVCC Ensembles: Ensembles:

• The average north-south and east-west The average north-south and east-west forecast forecast errors from the previous Atlantic errors from the previous Atlantic seasons seasons are computed for each forecast are computed for each forecast lead time.lead time.

• These These observedobserved errors are subtracted from errors are subtracted from the TCON and TVCN ensembles to the TCON and TVCN ensembles to generate the bias-corrected TCCN and generate the bias-corrected TCCN and TVCC forecasts.TVCC forecasts.



Bias Correction ExampleBias Correction Example

TVCN

TVCCBiased corrected

12

24

36

48

60

7284

Dolly


Recent Performance of Recent Performance of Intensity ForecastsIntensity Forecasts



Consensus Model DefinitionsConsensus Model DefinitionsNames will remain the same,Names will remain the same,

but models may changebut models may change

Name Type Members

ICONFixedGuidance from all models must be available

Decay SHIPS, GFDL,Logistic Growth Equation Model, Hurricane WRF

IVCN

VariableGuidance 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


2009 Atlantic Verification2009 Atlantic Verification

LGEM

HWRF

GFDL DecaySHIPS

FSSE Official

ICON


Atlantic Intensity ErrorsAtlantic Intensity Errorsvs. Five -Year Meanvs. Five -Year Mean

Official

2009

2004-8

2009Official forecast error was greater than five year mean, but the season was also more challenging than recent years.

Decay-SHIFOR5

2004-8


Intensity Forecast TrendsIntensity Forecast Trends Official Forecasts, Atlantic BasinOfficial Forecasts, Atlantic Basin

The goals of the Hurricane Forecast Improvement Project areto improve intensity forecasts by 20% in five years; 50% in 10 years.

OneSaffir-Simpson

Category

120 h

96 h

48 h

24 h

72 h



Atlantic BasinAtlantic Basin2009 Intensity Summary2009 Intensity Summary

• Intensity was more Intensity was more difficult to forecast in 2009difficult to forecast in 200911..

• Official intensity errorsOfficial intensity errors for the Atlantic basin in 2009 for the Atlantic basin in 2009 were mostly were mostly above the previous 5-yr meansabove the previous 5-yr means, but , but forecast forecast skill was at or just above historical highsskill was at or just above historical highs..

• The Logistic Growth model The Logistic Growth model (LGEM) performed best (LGEM) performed best – its second year in a row as the top model.– its second year in a row as the top model.

• The dynamical The dynamical GFDL and Hurricane WRF models GFDL and Hurricane WRF models performed poorly performed poorly – so poorly that the ICON– so poorly that the ICON 2 2 consensus was less accurate than the LGEM.consensus was less accurate than the LGEM.

11 as measured by Decay-SHIFOR (climatology + persistence)as measured by Decay-SHIFOR (climatology + persistence)2 2 Four-model (DSHP/LGEM/HWRF/GFDL) statistical-dynamic consensusFour-model (DSHP/LGEM/HWRF/GFDL) statistical-dynamic consensus


LGEM: Logistic GrowthLGEM: Logistic GrowthEquation ModelEquation Model



• The logistic equation was initially developedThe logistic equation was initially developed to to model population growthmodel population growth..

• The The rate of intensification rate of intensification is proportionalis proportional to the to the current intensity current intensity and the amount ofand the amount of available resourcesavailable resources..

• The The GFS model provides the forecast trackGFS model provides the forecast track and environmental parameters and environmental parameters the storm isthe storm is expected to encounter expected to encounter..

Logistic Growth ModelLogistic Growth Model



0

MaximumPossible

Inte

nsity

Time

EnvironmentMost Favorable

For Intensification EnvironmentSomewhat Favorable

For Intensification

EnvironmentSomewhat Favorable

For DissipationEnvironment

Most FavorableFor Dissipation

Initial Intensity



Predictor variables include:Predictor variables include:• Difference between current intensity and maximum Difference between current intensity and maximum

possible intensity (from weekly SST analyses).possible intensity (from weekly SST analyses).

• Vertical shear of the (850-200mb) horizontal wind.Vertical shear of the (850-200mb) 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).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.Intensification begins from the top down.

• Day of the year (Julian Day – 253 [Day of the year (Julian Day – 253 [Sept 10Sept 10thth]).]).

** averaged along forecast track only over the 24 hours prior to the valid time averaged along forecast track only over the 24 hours prior to the valid time

Statistical-Dynamic



Differences from SHIPS*:Differences from SHIPS*:• LGEM uses a logistic growth equation;LGEM uses a logistic growth equation;

SHIPS uses a regression 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 LGEM is more sensitive to environmental changes at the end of the forecast period.end of the forecast period.

• LGEM can better represent intensity changes of storms LGEM can better represent intensity changes of storms that move from water to land and then back over water.that move from water to land and then back over water.

**Statistical Hurricane Intensity Prediction SchemeStatistical Hurricane Intensity Prediction Scheme

Statistical-Dynamic

The SHIPS satellite-derived parameters are currently not in the LGEM forecast.


Adjustments to theAdjustments to theWidth of the Error ConeWidth of the Error Cone



Adjusted Error ConeAdjusted Error Cone

• The Error Cone is formed by enclosing the area swept The Error Cone is formed by enclosing the area swept out by a set of circles along the forecast track (at 12, out by a set of circles along the forecast track (at 12, 24, 36, … 120 hours).24, 36, … 120 hours).

• Two-thirds of the official forecast errors over a five Two-thirds of the official forecast errors over a five year sample fall within each circle.year sample fall within each circle.

• The same sized cone is used for all storms in the The same sized cone is used for all storms in the current season. current season.

http://www.nhc.noaa.gov/aboutcone.shtml


Adjusted Error ConeAdjusted Error ConeLeadTime

Radius (2007)

Radius (2008)

Radius (2009)

12 hours 39 n.mi. 39 n.mi. 36 n.mi.

24 69 67 62

36 99 92 89

48 124 118 111

72 179 170 167

96 252 233 230

120 326 305 302

http://www.nhc.noaa.gov/aboutcone.shtml

Remember:There is a one in three chance a storm will track outside the Error Cone.


Graphical Tropical Graphical Tropical Weather OutlookWeather Outlook



Graphical TropicalGraphical TropicalWeather OutlookWeather Outlook

Categories were adjusted in 2009 to reflect Categories were adjusted in 2009 to reflect verification from the 2008 hurricane season. verification from the 2008 hurricane season.

Low genesis probability: less than 30% (formerly 20%)Low genesis probability: less than 30% (formerly 20%)

Medium genesis probability: 30-50% (formerly 20-50%)Medium genesis probability: 30-50% (formerly 20-50%)

High genesis probability (over 50%)High genesis probability (over 50%)

Instead of Instead of lowlow//mediummedium//highhigh categories, categories, genesis probabilities will now be provided genesis probabilities will now be provided to the nearest 10%.to the nearest 10%.

http://www.nhc.noaa.gov/aboutgtwo.shtml


Graphical TropicalGraphical TropicalWeather OutlookWeather Outlook


Genesis Forecast VerificationGenesis Forecast Verification

Slight tendencyto over-forecastformation

General tendencyto under-forecastformation


The Saffir-SimpsonThe Saffir-SimpsonHurricane Hurricane WindWind Scale ScaleAll references to storm surge and flooding effects All references to storm surge and flooding effects

have been removedhave been removed



The Saffir-Simpson ScaleThe Saffir-Simpson Scale

• In 1967, the United Nations commissioned In 1967, the United Nations commissioned Herb Saffir Herb Saffir to study low-cost housing in regions of the world that to study low-cost housing in regions of the world that were prone to tropical cyclones and hurricanes.were prone to tropical cyclones and hurricanes.

• Saffir realized there was no way to describe the Saffir realized there was no way to describe the effects of a hurricane, so he effects of a hurricane, so he developed his own five-developed his own five-category scale.category scale.

• Robert SimpsonRobert Simpson, NHC Director, modified Saffir's , NHC Director, modified Saffir's work, work, adding lowest barometric pressures andadding lowest barometric pressures and

http://news.nationalgeographic.com/news/2005/12/1220_051220_saffirsimpson.html

a range of storm surge heights for a a range of storm surge heights for a given category.given category.

• In 1970, the National Hurricane Center In 1970, the National Hurricane Center started using the scale experimentally. started using the scale experimentally. It became operational in 1975.It became operational in 1975.

Hurricane Camille, 1969


Ike-Alicia ComparisonIke-Alicia Comparison

Ike (Cat 2)Alicia (Cat 3)


CategoryWind(mph)

Qualitativedamage estimate

Minimum Surface

Pressure (mb)

Stormsurge (ft)

One 74-95 Some >980 3-5

Two 96-110 Widespread 965-979 6-8

Three 111-130 Extensive 945-964 9-12

Four 131-155 Devastating 920-944 13-18

Five >155 Catastrophic <920 19+

The Saffir-Simpson Wind ScaleThe Saffir-Simpson Wind ScaleOperational for 2010Operational 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


New GOES-EastNew GOES-EastHurricane Rapid Scan Hurricane Rapid Scan

SectorSector



GOES-EastGOES-EastHurricane Rapid Scan SectorHurricane 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 Will provide up to four additional scans of the East and Central Tropical Atlantic per hour, in addition to and Central Tropical Atlantic per hour, in addition to the two standard scans.the two standard scans.

• Available August 1 - September 30.Available August 1 - September 30.

• Normal RSO requests to support NWS operations will Normal RSO requests to support NWS operations will take precedence over the research requests.take precedence over the research requests.

http://www.ssd.noaa.gov/PS/SATS/GOES/EAST/sched.html


For More Information…For More Information…

Upcoming VISIT Tropical Training SessionsUpcoming VISIT Tropical Training Sessionshttp://rammb.cira.colostate.edu/visit/topic_tropical.htmlhttp://rammb.cira.colostate.edu/visit/topic_tropical.html

NHC Forecast Model Background & InformationNHC Forecast Model Background & Informationhttp://www.nhc.noaa.gov/aboutmodels.shtmlhttp://www.nhc.noaa.gov/aboutmodels.shtml

Tropical Cyclone PredictionTropical Cyclone Predictionwww.meted.ucar.edu/tropical/textbook/ch11/obs_anl_pred_11_5.htmlwww.meted.ucar.edu/tropical/textbook/ch11/obs_anl_pred_11_5.html

An Overview of NHC Prediction ModelsAn Overview of NHC Prediction Modelswww.srh.noaa.gov/srh/ssd/nwpmodel/html/nhcmodel.htmwww.srh.noaa.gov/srh/ssd/nwpmodel/html/nhcmodel.htm

Advances and Challenges at the NHCAdvances and Challenges at the NHCWea. Forecasting, 24, 395-419 (April 2009)Wea. Forecasting, 24, 395-419 (April 2009)

Special thanks to James Franklin, Richard Pasch and the staff of the NWS NCEP’s 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. Tropical Prediction Center for information and materials used in this presentation. Thanks also to Lance Wood, WFO Houston/Galveston.Thanks also to Lance Wood, WFO Houston/Galveston.


Questions?Questions?

mailto: [email protected]

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