Andrea Schumacher 1 , Mark DeMaria 2 , John Knaff 3 , L iqun Ma 4 and Hazari Syed 5

1 C I R A , C o l o ra d o S tate U n i ve rs i t y, Fo r t C o l l i n s , C o l o ra d o2 N OA A / N WS / N H C , Mi a m i , F L

3 N OA A / N ES D I S / STA R , Fo r t C o l l i n s , C o l o ra d o4 N OA A / N ES D I S / O S P O, C o l l e ge Pa r k , Ma r y l a n d

5 N OA A / N ES D I S / O S P O, S SA I , C o l l e ge Pa r k , Ma r y l a n d

UPDATES TO THE NESDIS TROPICAL CYCLONE FORMATION PROBABILITY

PRODUCT

AMS 31st Conference on Hurricanes and Tropical Meteorology, San Diego, CA, 31 Mar 2014

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Motivation & Past Work (24-hr TCFP)Extending to 48 hrsAlgorithm OverviewExamples from 20132013 VerificationFuture Work

OUTLINE

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Need for objecti ve, real-ti me TC formati on guidanceDevelopment of NESDIS TC Formati on Probability (TCFP) product

Estimates probability of TC formation in next 24 hrs 5 x 5 degree latitude/longitude grid boxes Originally just in Atlantic and E. Pacific (2006), extended to N. W. Pacifi c

(2009), then made global (2013) Uses synoptic (GFS), convective (geostationary water vapor), and ocean

(Reynold’s SST) predictors

MOTIVATION & PAST WORK

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Offi cial forecast agencies provide 48-hr TC formati on products NHC Tropical Weather Outlook JTWC TC Formati on Alerts

Mismatch between TCFP guidance and user needs

Basic idea Use GFS forecast fi elds Satellite predictors most important at early

ti mes Challenges

Pre-TC disturbances can move far in 48 hours Fixed-domain scheme can’t account for moti on

Disturbance-following schemes have advantage Balancing increase in size spati al averaging vs.

loss of signal

EXTENDING TCFP TO 48 HOURS

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Discrete 5 x 5 degree grid boxes Some predictors would be divided between

2 grid boxes when disturbance at the edge of a grid box

E.g., PCCD (% cold cloud coverage) Would lead to “probability pulsing”

Introduced new spati al averaging 1-degree resolution domain 0-360E, 45S to 45N Value at each point is average over r =

500km (larger than 5 x 5 degree boxes) Sti ll some “probability pulsing” most

likely due to diurnal variations in convection

SPATIAL AVERAGING

R = 500 km

New product estimates the probability of TC formation within 500 km in the next 48 hours

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Development data ATL: 1995-2012 NEPA: 1998-2012 NWPA: 2000-2012 NIO: 2005-2012 SIO: 2005-2012 SHM: 2005-2012

Limiti ng dataset = water vapor imagery

Development done by basin

DATA

Predictor Source

VSHD - 850-200mb Vertical Shear (kt) GFS

RVOR - 850-mb Relative Vorticity (10-6s-1) GFS

MLRH - 600-mb Relative Humidity (%) GFS

THDV - Vertical Instability Parameter (°C) GFS

HDIV - 850-mb Horizontal Divergence (10-6s-1) GFS

MSLP - Mean Sea Level Pressure (mb) GFS

TADV - 850-mb Temperature Advection (10-6°Cs-1) GFS

BTWM - Cloud-cleared Brightness Temperature (°C) Water Vapor

PCCD - WV pixels Colder than -40 °C (%) Water Vapor

RSST - Reynold’s Weekly SST (°C) Reynolds

DNST - Distance to Nearest Active TC (km) ATCF

PLND - Land Coverage (%)

CPRB - Climatological TC Formation Probability (%) ATCF

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# non-genesis cases >> # genesis cases Screened out cases where one or more predictors were very hosti le

to genesis Screened out cases within 300 km of existi ng TC, over land For each predictor, found threshold for which less than 1% of

formati on cases occurred Examples for VSHD, RVOR, and MLRH:

SCREENING

Predictor name and units N. Atl N.E. Pac

N.W. Pac N.I.O. S. Pac* S.I.O.

VSHD - 850-200mb Vertical Shear (kt) >28.2 >21.4 >25.5 >28.1 >28.2 >22.1

RVOR - 850-mb Relative Vorticity (10-6s-1) <-1.0 <-0.8 <-0.4 <0.1 >0.1 >0.0

MLRH - 600-mb Relative Humidity (%) <22.3 <38.6 <32.9 <38.7 <29.8 <32.6

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Linear discriminant analysis (LDA) is a method used to fi nd a linear combinati on of predictors that separates two or more classes of events Here, classes are “genesis” and “non-genesis”

LDA fi nds coeffi cients provide max separati on in standard deviati on space

Top 4 contributi ng predictors by basin:

LINEAR DISCRIMINANT ANALYSIS

N. Atl N.E. Pac N.W. Pac N.I.O. S. Pac S.I.O.

RVOR CPRB RVOR RVOR RVOR RVOR

CPRB RVOR PCCD DNST PCCD PCCD

MSLP PCCD CPRB CPRB CPRB CPRB

PCCD MSLP MSLP TADV DNST MSLP

AMS 31st Conference on Hurricanes and Tropical Meteorology 9

LDA y ie lds a l inear functi on (F) that provides binary c lass ifi cati on Genesis or No Genesis

However, F i tse l f i s not b inary Separated genesis cases into 10 equal b ins by F and computed genesis f requency

ESTIMATING 48-HR PROBABILITY

F1 F2 # Gen Cases # Total Gen Freq (%)

-12.57 -7.25 1571 4364950 0.04

-7.25 -6 1572 538332 0.29

-6 -4.99 1572 260000 0.6

-4.99 -4.07 1572 151302 1.03

-4.07 -3.21 1572 94607 1.63

-3.21 -2.36 1572 64606 2.38

-2.36 -1.38 1572 50284 3.03

-1.38 -0.25 1572 36269 4.15

-0.25 1.38 1572 26782 5.54

1.38 8.5 1581 16985 8.52

P(24h U 48h) = P(24h) + P(48h) + P(24h ∩ 48h)

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PRODUCT EXAMPLES

36 hours prior to 2 genesis events:Manuel (E Pac)Man-Yi (NW Pac)

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2013 VERIFICATION

ATL NEPA NWPA NIO SIO SHEM

Brier Skill Score (wrt Clim) 0.018 0.044 0.066 0.046 0.034 0.077

Multiplicative Bias 0.81 0.71 0.47 0.49 1.01 0.97

Max Probability Genesis (%) 24.3 47.9 17.3 22.4 18.8 28.2

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EXCEL HAS FAILED ME THIS MORNING!!!!

Basic takeaway from plots Under-predicti on in all basins

2013 VERIFICATION - RELIABILITY

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Tropical Weather Outlook includes 120-hr formati on probability New in 2013

From a practi cal standpoint, extending TCFP to 120 hours is straightf orward

Challenge: Disturbance moti on may be even bigger problem Increase size of spatial averages? Preliminary work underway

Hybrid TCFP / disturbance-following genesis model E.g., TCGI, regional dynamical model TCFP can identify regions of highest formation likelihood Trigger disturbance-centric model

FUTURE WORK

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TCFP extended to 48 hours htt p://www.ssd.noaa.gov/PS/TROP/TCFP/index.html

New spati al averaging scheme works well Increased overall probabiliti es

24hr product: 10-20% 48hr product: 20-50%

Sti ll systemati cally underpredicti ng, especially at higher probabiliti es

Brier skill scores suggest higher skill than climatology

SUMMARY

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References

QUESTIONS?