(NRL Base-funded project) Project Title and Principal Investigator Background Scientific Objectives Field Experiment Requirements Tropical Cyclone Structure-2008 (TCS-08) ONR/NRL Funded Projects Extratropical transitions (ET) of Tropical Cyclones (TCs) are often accompanied by hemispheric drops in forecast skill (e.g., Jones et al. 2003 Wea. and For.). Observations in sensitive regions have bigger impact during ET than during other periods (Cardinali et al. 2007 QJRMS) Stochastic convection has significant impact on ensemble behavior in tropics (Reynolds et al. 2008) and on ensemble TC tracks. Tyranny of Scales (NRL Base-funded project) Carolyn A. Reynolds (carolyn.reynolds@nrlmry.navy.mil) Naval Research Laboratory Monterey, CA 93943 Use Singular Vector (SV) sensitivity and field observations to learn about important large-scale mechanisms impacting TC predictability during recurvature and ET. Assess the ability of SVs to identify sensitive regions, in comparison with other targeting techniques. Determine if observations in sensitive regions have larger impact on forecasts of TC recurvature and ET than observations in non-sensitive regions. Determine if unresolved processes are having significant impact on predictability through ensemble experiments. Sample sensitive regions during recurvature and extratropical transitions using the C130 and Falcon dropsonde measurements, off-time soundings, and additional satellite data. Sample non-sensitive regions as well, so post-time data impact comparisons may be made. Have as much data as possible on GTS for real-time and post-time assimilation.