Targeting strategies to improve hurricane track forecasts (JHT 03-05)

1. Targeting strategies to improve hurricane track forecasts (JHT 03-05) PIs: Dr Sharanya J. Majumdar (University of Miami) Dr Sim D. Aberson (NOAA/AOML/HRD) Co-PIs:Dr Zoltan Toth (NOAA/NWS/NCEP/EMC), Ms Lacey D. Holland (SAIC at EMC), Dr Brian J. Etherton (UNC Charlotte), Mr Paul Leighton (NOAA/AOML/HRD) (Acknowledgment: Mr Richard Wobus (EMC)) Interdepartmental Hurricane Conference, Charleston, SC. March 3rd 2004

2. Targeted Observations • Motivation • To improve tropical cyclone track and intensity forecasts by selective deployments of observations in the storm’s environment. • NOAA G-IV Synoptic Surveillance missions use targeted GPS dropwindsondes. • Present strategy: direct aircraft towards locations in which the “spread” (or standard deviation) of an ensemble forecast is large at the observation time.

3. Ensemble Spread Fcst for 2003091400: Isabel x x : Isabel’s Center

4. New Targeting Strategy • Ensemble Transform Kalman Filter (ETKF) • Has been used operationally by NWS for Winter Storm Reconnaissance since 2001 • Theory: Bishop et al. (MWR, 2001) • Targeted Observations: Majumdar et al. (QJRMS 2001, MWR 2002, QJRMS 2002) • Ensemble Initialization: Wang and Bishop (JAS, 2003) • Data Assimilation: Etherton and Bishop (MWR, 2004)

5. How the ETKF works Ensemble Initialization time Decision time Targeted Observing (analysis) time Verification time ti td ta tv t ETKF uses operational ensemble forecasts to rapidly predict signal variance = reduction in error variance for any deployment q of adaptive observations: Sq = PN – Pq = MPN(ta)HqT (HqPN(ta)HqT+R)-1HqPN(ta) MT = ZN(tv)TNCq Gq (Gq+I)-1 CqT TNTZNT(tv)

6. Summary Maps of Signal Variance ETKF predicts signal variance (reduction in forecast error variance) for all feasible deployments of targeted observations. Summarize these predictions in the form of a map or bar chart.

7. ETKF Summary Map: Isabel

8. ACTUAL NCEP GFS SIGNAL ETKF PREDICTED SIGNAL VAR. ETKF predicts the variance of the “signal” : the impact of the targeted observations on the operational forecast. Impact on GFS analysis Impact on 1-day forecast Preliminary result from Hurricane Isabel ETKF uses 20-member 1-degree res NCEP GFS Ensemble, initialized 24-36h prior to targeted observing time. Impact on 2-day forecast

9. Ongoing Work • Examine 2003 targeting missions (5 Atlantic, 2 NW Pacific cyclones): Develop ETKF further, e.g. investigate vortex removal techniques and focus on storm asymmetries • Extend to “norms” of hurricane track and intensity (currently using simple norm of wind speed, which is used in WSR) • Synoptic assessment of ETKF summary maps and signal variance propagation • Quantitative tests of ETKF’s ability to predict signal variance and reduction in forecast error variance • Adapt scripts to run for GFDL and SHIPS models

10. Ongoing Work • ECMWF 1-deg ensembles are now available (Jan 04), and NCEP GFS 1-deg ensembles will soon be produced beyond 84h • ETKF software is being developed within the framework of Winter Storms: easy interface • Work in progress disseminated on Web site: http://orca.rsmas.miami.edu/~majumdar/tc/

11. Summer 2004 – Summer 2005 • Run improved ETKF for 1-deg ensembles for synoptic surveillance cases in upcoming 2004 hurricane season. • Regular communication with NHC once satisfactory version of ETKF is developed. • Communication with Taiwan (Dr Chun-Chieh Wu): Advising targeted observing locations for typhoon reconnaissance. • Combine ETKF software with flight track design software developed by Dr Sim Aberson under JHT funding. • Transition of ETKF software to operations.