NASA uses satellite data to calculate the amount of rainfall generated from tropical cyclones, and used that capability for the Eastern Pacific Ocean's Hurricane Willa.
Tropical Depression 24E formed on October 20, 2018 and later in the day became tropical storm Willa. The tropical depression rapidly intensified and was a category five hurricane with winds of over 161 mph (140 knots) on October 22. Willa had weakened to category three intensity when it made landfall in Sinaloa, Mexico on October 24, 2018. Moisture streaming from Willa's remnants added to the soaking of the already water logged state of Texas. Moisture from Willa's remnants contributed to storms over the Southeast and to the developing Nor'easter moving over the East Coast.
At NASA's Goddard Space Flight Center in Greenbelt, Maryland a rainfall accumulation analysis was generated by totaling Integrated Multi-satellitE Retrievals for GPM (IMERG) data for the period from October 20 to 26, 2018. The IMERG rainfall accumulation data indicated that Willa produced rainfall totals greater than 20 inches (508 mm) in the Pacific Ocean off Mexico's coast. IMERG data also indicated that rainfall accumulations of over 15 inches (381 mm) occurred in parts of Mexico and Southeastern Texas.
IMERG data are generated every half hour by NASA's Precipitation Processing System by merging data from the satellites in the GPM Constellation, and calibrating those data with measurements from the GPM Core Observatory as well as rain gauge networks around the world. IMERG data are provided for much of the globe. Full coverage is calculated over latitudes from 60 degrees north to 60 degrees south with the remaining areas of the globe being partially covered.
The Integrated Multi-satellitE Retrievals for GPM (IMERG) creates a merged precipitation product from the GPM constellation of satellites. These satellites include DMSPs from the U.S. Department of Defense, GCOM-W from the Japan Aerospace Exploration Agency (JAXA), Megha-Tropiques from the Centre National D'etudies Spatiales (CNES) and Indian Space Research Organization (ISRO), NOAA series from the National Oceanic and Atmospheric Administration (NOAA), Suomi-NPP from NOAA-NASA, and MetOps from the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). All of the instruments (radiometers) onboard the constellation partners are intercalibrated with information from the GPM Core Observatory's GPM Microwave Imager (GMI) and Dual-frequency Precipitation Radar (DPR).
GPM is a joint mission between NASA and the Japan Aerospace Exploration Agency, JAXA.