The remnants of Hurricane Polo are bringing a historic flood threat to the US Southwest, Texas and the Plains, forecasters said on Tuesday. Atmospheric moisture was near or above record levels for late September over parts of the Southwest, Texas and Oklahoma, according to weather.com. The National Weather Service issued a Level 3 out of 4 moderate risk of excessive rainfall. Polo made landfall in western Mexico, dumping 4 to 8 inches of rain in Sonora, with isolated totals of 8 inches. Its moisture is now fuelling repeated rounds of thunderstorms across New Mexico and Texas. El Paso remained under a flood watch and wind advisory through Wednesday morning. Texas Governor Greg Abbott warned of possible tropical tornadoes as the system moved inland. Emergency officials urged residents to avoid flooded roads. Context: Flash flooding is the leading cause of weather-related deaths in the US, according to the National Weather Service.