Andrea Schumacher 1, Mark DeMaria 2, John Knaff 3, Liqun Ma 4 and Hazari Syed 5 1 CIRA, Colorado State University, Fort Collins, Colorado 2 NOAA/NWS/NHC, Miami, FL 3 NOAA/NESDIS/STAR, Fort Collins, Colorado 4 NOAA/NESDIS/OSPO, College Park, Maryland 5 NOAA/NESDIS/OSPO, SSAI, College Park, Maryland UPDATES TO THE NESDIS TROPICAL CYCLONE FORMATION PROBABILITY PRODUCT AMS 31 st Conference on Hurricanes and Tropical Meteorology, San Diego, CA, 31 Mar 2014

 Motivation & Past Work (24-hr TCFP)  Extending to 48 hrs  Algorithm Overview  Examples from 2013  2013 Verification  Future Work OUTLINE AMS 31st Conference on Hurricanes and Tropical Meteorology 2

 Need for objective, real-time TC formation guidance  Development of NESDIS TC Formation 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. Pacific (2009), then made global (2013)  Uses synoptic (GFS), convective (geostationary water vapor), and ocean (Reynold’s SST) predictors MOTIVATION & PAST WORK AMS 31st Conference on Hurricanes and Tropical Meteorology 3

 Official forecast agencies provide 48-hr TC formation products  NHC Tropical Weather Outlook   JTWC TC Formation Alerts  Mismatch between TCFP guidance and user needs  Basic idea  Use GFS forecast fields  Satellite predictors most important at early times  Challenges  Pre-TC disturbances can move far in 48 hours  Fixed-domain scheme can’t account for motion  Disturbance-following schemes have advantage  Balancing increase in size spatial averaging vs. loss of signal EXTENDING TCFP TO 48 HOURS AMS 31st Conference on Hurricanes and Tropical Meteorology 4

 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 spatial 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)  Still some “probability pulsing”  most likely due to diurnal variations in convection SPATIAL AVERAGING AMS 31st Conference on Hurricanes and Tropical Meteorology 5 R = 500 km New product estimates the probability of TC formation within 500 km in the next 48 hours

 Development data  ATL:  NEPA:  NWPA:  NIO:  SIO:  SHM:  Limiting dataset = water vapor imagery  Development done by basin AMS 31st Conference on Hurricanes and Tropical Meteorology 6 DATA PredictorSource VSHD mb Vertical Shear (kt) GFS RVOR mb Relative Vorticity (10-6s-1) GFS MLRH mb Relative Humidity (%) GFS THDV - Vertical Instability Parameter (°C) GFS HDIV mb Horizontal Divergence (10-6s-1) GFS MSLP - Mean Sea Level Pressure (mb) GFS TADV 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

 # non-genesis cases >> # genesis cases  Screened out cases where one or more predictors were very hostile to genesis  Screened out cases within 300 km of existing TC, over land  For each predictor, found threshold for which less than 1% of formation cases occurred  Examples for VSHD, RVOR, and MLRH: SCREENING AMS 31st Conference on Hurricanes and Tropical Meteorology 7 Predictor name and unitsN. Atl N.E. Pac N.W. Pac N.I.O.S. Pac*S.I.O. VSHD mb Vertical Shear (kt)>28.2>21.4>25.5>28.1>28.2>22.1 RVOR mb Relative Vorticity (10 -6 s -1 )<-1.0<-0.8<-0.4<0.1>0.1>0.0 MLRH mb Relative Humidity (%)<22.3<38.6<32.9<38.7<29.8<32.6

 Linear discriminant analysis (LDA) is a method used to find a linear combination of predictors that separates two or more classes of events  Here, classes are “genesis” and “non-genesis”  LDA finds coefficients provide max separation in standard deviation space  Top 4 contributing predictors by basin: LINEAR DISCRIMINANT ANALYSIS AMS 31st Conference on Hurricanes and Tropical Meteorology 8 N. AtlN.E. PacN.W. PacN.I.O.S. PacS.I.O. RVORCPRBRVOR CPRBRVORPCCDDNSTPCCD MSLPPCCDCPRB PCCDMSLP TADVDNSTMSLP

 LDA yields a linear function (F) that provides binary classification  Genesis or No Genesis  However, F itself is not binary  Separated genesis cases into 10 equal bins by F and computed genesis frequency ESTIMATING 48-HR PROBABILITY AMS 31st Conference on Hurricanes and Tropical Meteorology 9 F1F2# Gen Cases# TotalGen Freq (%) P(24h U 48h) = P(24h) + P(48h) + P(24h ∩ 48h)

AMS 31st Conference on Hurricanes and Tropical Meteorology 10 PRODUCT EXAMPLES 36 hours prior to 2 genesis events: Manuel (E Pac) Man-Yi (NW Pac)

AMS 31st Conference on Hurricanes and Tropical Meteorology VERIFICATION ATLNEPANWPANIOSIOSHEM Brier Skill Score (wrt Clim) Multiplicative Bias Max Probability Genesis (%)

 EXCEL HAS FAILED ME THIS MORNING!!!!  Basic takeaway from plots  Under-prediction in all basins 2013 VERIFICATION - RELIABILITY AMS 31st Conference on Hurricanes and Tropical Meteorology 12

 Tropical Weather Outlook includes 120-hr formation probability  New in 2013  From a practical standpoint, extending TCFP to 120 hours is straightforward  Challenge: Disturbance motion 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 AMS 31st Conference on Hurricanes and Tropical Meteorology 13

 TCFP extended to 48 hours   New spatial averaging scheme works well  Increased overall probabilities  24hr product: 10-20%  48hr product: 20-50%  Still systematically underpredicting, especially at higher probabilities  Brier skill scores suggest higher skill than climatology SUMMARY AMS 31st Conference on Hurricanes and Tropical Meteorology 14

 References QUESTIONS? AMS 31st Conference on Hurricanes and Tropical Meteorology 15