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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