A Global A Global Tropical Tropical Cyclone Cyclone
Formation Formation Probability Probability
ProductProductAndrea Schumacher, CIRA/CSUAndrea Schumacher, CIRA/CSUMark DeMaria and John Knaff, Mark DeMaria and John Knaff,
NOAA/NESDIS/StARNOAA/NESDIS/StARDaniel Brown, NHCDaniel Brown, NHC
6464thth Interdepartmental Hurricane Conference Interdepartmental Hurricane Conference1-4 March, 20101-4 March, 2010Savannah, GASavannah, GA
MotivationMotivation
Agencies required to forecast TC genesisAgencies required to forecast TC genesis
Of varying priority (NHC/CPHC=7, JTWC=3)Of varying priority (NHC/CPHC=7, JTWC=3)
Numerical global modelsNumerical global models Getting better as resolution improvesGetting better as resolution improves Tendency towards overpredictionTendency towards overprediction Unknown biasesUnknown biases
Statistical guidance Statistical guidance Lack of real-time, objective statistical guidanceLack of real-time, objective statistical guidance May be due to rarity of formation (needle in a May be due to rarity of formation (needle in a
haystack)haystack)
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Overview of TC Formation Overview of TC Formation Probability (TCFP) Probability (TCFP)
ProductProduct Available for N Atlantic (2006), NE Pacific Available for N Atlantic (2006), NE Pacific
(2006) and NW Pacific (2008) basins.(2006) and NW Pacific (2008) basins.
Uses large-scale environmental and Uses large-scale environmental and convective predictorsconvective predictors
3-step statistical scheme (Screening, LDA, 3-step statistical scheme (Screening, LDA, Probability)Probability)
24-hour probability of TC formation over 24-hour probability of TC formation over each 5 x 5 degree lat/lon grid box in domaineach 5 x 5 degree lat/lon grid box in domain
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Input ParametersInput ParametersABBREV Parameter Description Source
LAT Latitude (°) ATCF
PLAND % land coverage Land covrge
DSTRM Distance to nearest TC (km) ATCF
SST Sea surface temp (°C) Reynolds
VSHEAR 850-200 hPa vertical shear (kt) NCEP GFS
CIRC 850 hPa circulation (kt) NCEP GFS
THDEV Vertical instability (°C) NCEP GFS
HDIV 850 hPa horizontal divergence (m/s) NCEP GFS
SLP Sea-level Pressure (hPa) NCEP GFS
PCCOLD % coverage by pixels colder than -40°C Sat WV
BTWARM Avg. cloud-cleared brightness temp (°C) Sat WV
CPROB Climatological formation probability Best Track464th Interdepartmental Hurricane Conference 3 March 2010
Recent Product Recent Product ImprovementsImprovements Extended to Indian Ocean and S. HemisphereExtended to Indian Ocean and S. Hemisphere
Added 2006-2008 to development datasetAdded 2006-2008 to development dataset
Experimental version running since Aug 2009Experimental version running since Aug 2009
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Most Important Most Important PredictorsPredictors
Same predictors most important in all basinsSame predictors most important in all basins However, However, rankrank of importance varies of importance varies
NORMALIZED COEFFICIENTS
NATL NEP NWP NIO SIO SPAC
Clim Formation Prob 1.6 1.6 0.9 1.6 1.5 1.4
Circulation (850-mb) 1.3 1.3 1.5 1.9 1.5 1.8
Cold Cloud Coverage 0.7 0.7 0.9 0.6 0.8 0.7
Distance to Existing TC 0.7 0.6 1.0 0.7 0.6 0.7
N. Indian Ocean
S. Indian Ocean
N.W. Pacific
S. Pacific
N.E. Pacific
N. Atlantic
S. Atlantic
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Verification SummaryVerification Summary1995-20081995-2008
Brier skill scores and ROC skill scores Brier skill scores and ROC skill scores All positive All positive forecasts more skillful than forecasts more skillful than
climatologyclimatology Small Small skill could be better skill could be better
ReliabilityReliability Overpredicts at high prob in N. AtlOverpredicts at high prob in N. Atl Underpredicts at high probs in all other basinsUnderpredicts at high probs in all other basins
Gridbox-to-gridbox comparisons may be too Gridbox-to-gridbox comparisons may be too strictstrict Consider fuzzy verification methodsConsider fuzzy verification methods
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2009 – Tropical Atlantic2009 – Tropical Atlantic
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2009 – NE Pacific2009 – NE Pacific
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2009 – NW Pacific2009 – NW Pacific
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N. Indian Ocean (2009)N. Indian Ocean (2009)
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S. Hemisphere (2009)S. Hemisphere (2009)
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Current StatusCurrent Status
Objective TC formation guidance productObjective TC formation guidance product Global domainGlobal domain Automated, real-timeAutomated, real-time Displays real-time, climatology, and anomaly Displays real-time, climatology, and anomaly
plots of formation probability and input plots of formation probability and input parametersparameters
LimitationsLimitations Essentially a nowcastEssentially a nowcast Low probability values (10-25% max)Low probability values (10-25% max) Skill relative to climatology is moderateSkill relative to climatology is moderate
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Next Goal: Extend Next Goal: Extend ForecastForecast
Be consistent with NHC Genesis Be consistent with NHC Genesis Probabilities (48 hrs)Probabilities (48 hrs)
GFS forecast fields (extend to 5 days)GFS forecast fields (extend to 5 days)
Use larger-scale averages of convective Use larger-scale averages of convective parametersparameters
Explore new predictorsExplore new predictors
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Thank You!Thank You!
ReferencesReferences Schumacher, A.B., M. DeMaria, and J.A. Knaff, Schumacher, A.B., M. DeMaria, and J.A. Knaff,
2009: Objective Estimation of the 24-h 2009: Objective Estimation of the 24-h Probability of Tropical Cyclone Formation. Probability of Tropical Cyclone Formation. Wea. Forecasting, 24, 456–471.Wea. Forecasting, 24, 456–471.
DeMaria, M., J.A. Knaff, and B.H. Connell, DeMaria, M., J.A. Knaff, and B.H. Connell, 2001: A Tropical Cyclone Genesis Parameter 2001: A Tropical Cyclone Genesis Parameter for the Tropical Atlantic. for the Tropical Atlantic. Wea. Forecasting, 16, Wea. Forecasting, 16, 219–233.219–233.
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