https://phys.org/news/2018-10-nasa-sergio-southwest.html

Infrared data provides temperature information. MODIS found strongest storms with coldest cloud top temperatures as cold as minus 63 degrees Fahrenheit (minus 53 Celsius) in a small area in northwestern Mexico. NASA research has shown that cloud tops with temperatures that cold were high in the troposphere and have the ability to generate heavy rain.  A large area of storms with cloud top temperatures near minus 50 degrees Fahrenheit blanketed most of Baja California, northwestern mainland Mexico and stretched into southern Arizona.

Soon after Aqua passed overhead, Sergio entered the Sea of Cortez, located between Baja California and mainland Mexico.