ONE OF THE MOST CHALLENGING ASPECTS IN PREDICTION OF TROPICAL CYCLONES (TCS) IS THE COMPLEX INTERACTIONS AMONG THE TC CONVECTIVE SYSTEMS AIR-SEA FLUXES AND ENVIRONMENTAL CONDITIONS. OCEAN SURFACE WIND AND AIR-SEA FLUXES AND ARE DIFFICULT TO OBSERVE IN TCS. THE ONLY FEASIBLE WAY TO CONTINUOUSLY OBSERVE SURFACE WIND OVER THE GLOBAL OCEAN IS TO MEASURE THEM FROM SPACE. THE SPACE-BASED REMOTE SENSING TECHNIQUES FOR SURFACE WIND DEPEND CRITICALLY ON THE PROPERTIES OF THE SEA SURFACE THAT ARE USUALLY DOMINATED BY LARGE OCEAN SURFACE WAVES AND CURRENT UNDER EXTREME HIGH WIND CONDITIONS IN TCS. THE PROPOSED RESEARCH AIMS TO I) BETTER UNDERSTAND AIR-SEA INTERACTION AND THE UNCERTAINTY OF SURFACE WIND OBSERVATIONS ASSOCIATED WITH THE VARIABILITY OF OCEAN SURFACE WAVES AND CURRENT AND II) IMPROVE PREDICTION OF TCS USING THE CYGNSS DATA OBSERVATIONS FROM THE NASA CONVECTIVE PROCESS EXPERIMENT (CPEX) 2017 FIELD CAMPAIGN AND A HIGH-RESOLUTION FULLY COUPLED ATMOSPHERE-WAVE-OCEAN MODEL. THIS PROPOSED RESEARCH WILL FOCUS ON THREE SPECIFIC OBJECTIVES: 1) EVALUATE CYGNSS WIND AND MEAN SQUARE SLOPE (MSS) DATA USING THE SURFACE WIND OBSERVATIONS FROM GPS DROPWINDSONDES DOPPLER WIND LIDAR (DAWN) AND THE AIR-SEA INTERFACE DATA WITH OCEAN SURFACE WAVES FROM THE NDBC BUOYS DURING THE NASA CPEX 2017 FIELD CAMPAIGN INCLUDING DATA COLLECTED IN TROPICAL STORM CINDY (2017) 2) INVESTIGATE THE AIR-SEA INTERACTION AMONG THE SURFACE WIND OCEAN SURFACE WAVES AND CURRENT AND QUANTIFY THE UNCERTAINTY OF WAVES AND CURRENT ON SURFACE WIND USING BOTH CYGNSS DATA AND A HIGH-RESOLUTION FULLY COUPLED ATMOSPHERE-WAVE-OCEAN MODEL AND 3) CONDUCT HURRICANE PREDICTION EXPERIMENTS USING THE COUPLED MODEL FOR 2017 HURRICANES INCLUDING HARVEY IRMA AND MARIA AND EVALUATE/VERIFY MODEL RESULTS WITH CYGNSS DATA. THESE RESEARCH RESULTS WILL HAVE A SIGNIFICANT IMPLICATION AND CONTRIBUTION TO TC IMPACTS FORECASTING INCLUDING STORM SURGE DURING HURRICANE LANDFALLS. THE OUTCOME OF THIS STUDY IS EXPECTED TO IMPROVE TC PREDICTIONS THROUGH A BETTER UNDERSTANDING AND MODELING OF THE AIR-SEA INTERACTION AFFECTING SURFACE WIND WAVES CURRENT AND AIR-SEA FLUXES AS WELL AS THEIR FEEDBACK ON TC EVOLUTION AND STORM IMPACTS ON THE COASTAL REGIONS. THIS PROPOSED STUDY WILL PRIMARILY ADDRESS THE FOLLOWING NASA CYGNSS RESEARCH OBJECTIVES IN THE ROSES SOLICITATION A.52 (CYGNSS COMPETED SCIENCE TEAM): 3.1 QUANTITATIVE DATA PRODUCTS AND/OR ANALYSES FOCUSING ON SURFACE WIND AND/OR AIR-SEA INTERACTIONS AND 3.3 STORM SURGE. THIS RESEARCH BUILDS ON THE PIS PREVIOUS WORK ON OBSERVATIONS AND COUPLED ATMOSPHERE-WAVE-OCEAN MODELING OF TCS. THE RESULTS OF THIS PROJECT COULD BE TRANSFORMATIVE THROUGH THE UNIQUE HIGH TEMPORAL AND GLOBAL OBSERVATIONS OF TCS BY CYGNSS.