Analysis of the Extreme Rainfall Events during Hurricane Harvey and Tropical Storm Allison

On June 5th, 2001, Tropical Storm Allison made landfall west of Galveston, Texas with maximum sustained wind speeds of 22 m/s. This storm produced over 940 mm of rain, caused 22 fatalities, and cost upwards of $5 billion dollars. On August 25th, 2017, Hurricane Harvey made landfall near Corpus Christi, Texas as a Category Four hurricane with maximum sustained wind speeds of 58 m/s. Hurricane Harvey produced highest rainfall totals of 1270 mm in some areas of Houston, Texas, caused 77 deaths, and estimated damages are still being calculated but have reached over $180 billion dollars. Meteorological data from genesis to landfall of Hurricane Harvey and Tropical Storm Allison were used to compare the two storms with a focus on the diurnal impacts the storm had on rainfall intensity. The purpose of this study was to identify which of the favorable characteristics for tropical cyclone intensification allowed these two storms to strengthen and produce the significant amount of rain during their lifespans in the Houston, Texas area. The favorable conditions that influenced the genesis and the intensification of these storms were sea surface temperature, low-level wind shear, convection, and general atmospheric circulation along their trajectories. Special attention was given to the spatial and temporal development of precipitation and wind speeds, as well as travel time and path of these tropical systems after landfall since these conditions caused most of the damage. This work investigated the diurnal impact of the stable nocturnal boundary layer and the increased inflow that caused deep moist convection, which resulted in both storms producing most of their rainfall at night. The methods used to study these storms were based on analysis of pertinent data (e.g., distribution of temperature, humidity and convective available potential energy [CAPE] at different atmospheric levels) provided from the National Weather Service/National Oceanic and Atmospheric Administration (NWS/NOAA).