# Performance Evaluation of IMERG GPM Products during Tropical Storm Imelda
## 1 Introduction  
The U.S. has faced around 258 weather and climate disasters, each of which reached an overall damage exceeding a billion dollars, since 1980. The National Centers for Environmental Information (NCEI), a subsidiary of the National Oceanic and Atmospheric Association (NOAA), records weather and climate events with significant economic and societal impacts in the United States [1]. The total cost of all of these disasters exceeded an estimated damage cost of 1.75 trillion dollars. During 2019 alone, the U.S. experienced 14 separate billion-dollar disasters, and 2019 was marked as the fifth consecutive year (2015-2019) in recorded history with 10 or more individual billion-dollar disasters [1]. The natural disasters in 2019 included: three major inland floods, eight severe storms, two tropical cyclones or depressions (Dorian and Imelda), and one major wildfire event; totaling an overall damage cost exceeding 14 billion dollars [1]. The state of Texas currently leads the nation in the total number of billion-dollar disasters since 1980, with a total estimated damage cost of around 250 billion dollars [2]. In recent history, Texas has experienced some of the nation's deadliest and most expensive natural disasters, such as the Memorial Day Flood (2015), Tax Day Flood (2016), Hurricane Harvey (2017), The Great June Flood (2018), and Tropical Storm Imelda (2019) [3]. Major drivers of these natural disasters were extreme precipitation and heavy downpour, which have left scientists and researchers looking for solutions to better model and predict such extreme scenarios. About three billion or nearly half of the world's population lives in coastal areas, and in the United States the southern coastal states like Louisiana, Florida, and Texas face recurring extremehydrological events [4; 5; 6]. In the future, Texas will likely face similar extreme natural disasters, and the need for accurate precipitation estimates is key to better understand and model these hydrological scenarios. The National Hurricane Center started monitoring an area of disturbed weather for possible tropical development near the west coast of Florida on 14 September 2019 [7]. The area of disturbed weather had moved westward by 16 September, reaching the coast of Southeast Texas and Southeast Louisiana. Before daybreak on 17 September, the disturbed weather area underwent significant organization and was being observed by the GOES satellite and the Houston, TX and Lake Charles, and LA WSR-88D radars. By midday, the weather area strengthened, and soon after, it was classified as Tropical Storm Imelda by the National Hurricane Center (NHC) tropical cyclone update. Around 1:30 PM on 17 September 2019, Tropical Storm Imelda made landfall near Freeport, Texas, and was weakened to a tropical depression by the evening. It moved inland shortly after and hovered between Houston and Lufkin in Texas throughout 19 September. During the stalling of Imelda over Southeast Texas, precipitation events caused significant flooding in the Houston and Galveston areas. Along the I-10 corridor from Winnie eastward to Fannett, Beaumont, Vidor, and Orange Texas faced devastating flooding in many areas. Tropical Storm Imelda was the fifth wettest tropical cyclone in the history of the continental United States and the fourth wettest in the state of Texas [7]. It inflicted damage worth over 5 billion dollars [7]. To analyze the impacts of these severe natural disasters, scientists have been trying to evaluate different precipitation estimate tools in terms of their performance and accuracy. Precipitation modeling is an essential part of weather prediction, hydrological analysis, climate modeling, and agricultural applications [8; 9; 10]. Accurate precipitation predictions are crucial for the analysis of impacts caused by natural disasters such as hurricanes, tropical storms, and tornadoes [11].