Air-Sea Interactions, Vertical Motions, High Winds, and Heavy Precipitation Associated with Land Falling Tropical Storm Lee over Gulf of Mexico using Remote Sensing and Satellite Data

Abstract

Tropical Storm (TS) Lee formed on September 2, 2011 from a broad but disorganized tropical wave that entered Western Caribbean in late August. While core of storm meandered inland on September 4 roughly 50 miles (80 km) southwest of Lafayette, LA, squalls impacted Gulf Coast the day prior. On September 4^th, T.S Lee pressure drops to 986 mob and begins to make landfall on Louisiana-Mississippi coast. On September 5^th, Lee makes landfall. Lee’s high moisture content and slow speed promoted 24-hour rainfall totals in excess of 5 inches (127 mm) to 11 inches (281 mm) in most locations over Gulf States. Finally, on September 6^th, remnants of T.S Lee absorbed by cold front. 93L interacts with an upper-level low pressure system and slowly intensifies, observed at 200 mb surface map. Strong upper-level winds from west-northwest generated 30 knots of wind shear over 93L, keeping heaviest thunderstorms disorganized. Alongside cold, dry air aloft, these mechanisms hampered 93L’s intensification. Depression positioned south of high-pressure ridge provided weak steering currents. SST’s at 88°F (31.3°C) provided plenty of energy for heavy rain potential. Climatic conditions persist, albeit intensification upgrade towards tropical storm. Bulk of T.S Lee remained over prime Gulf waters as paradoxical situation occurred—though high pressure-ridge slowed systems movement allowing potential intensification, simultaneous influx of cold dry air from west quadrant (alongside moderate wind-shear) diminished T.S Lee’s intensification ability. Despite lacking wind/pressure intensity, T.S Lee absorbed large amounts of moisture, contributing to intense precipitation. We further investigated possible relationships between large-scale heat fluxes and intensity changes associated with landfall of T.S Lee, and examining vertical motions associated with intensity change of T.S. Data on Convective Available Potential Energy (CAPEV), sea level pressure, and wind speed were obtained from Atmospheric Soundings and NOAA National Hurricane Center (NHC), respectively for period of August 25 to September 10, 2011. We developed an empirical model and C++ program to calculate surface potential temperatures and heat fluxes using above data. Vertical motions were computed using CAPEV values. Studies showed large-scale heat fluxes reached maximum (4500W/m2) with central pressure 988 mob. Convective Available Potential Energy (CAPEV) and vertical motions peaked during landfall. Large vertical atmospheric motions associated with land falling T.S Lee produced severe weather including thunderstorms, tornadoes and heavy precipitation.