Tropical Depression Twenty-E (TD20E) formed on October 20, 2015 off the Mexican coast southeast of Puerto Escondido, Mexico. Later that evening TD20E was upgraded to tropical storm Patricia.

On October 21, 2015 at 1634 UTC (11:34 AM CDT) the GPM core observatory satellite flew over tropical storm Patricia. GPM's Microwave Imager (GMI) instrument had good coverage of the rainfall associated with the tropical storm. Rainfall data derived from GMI are shown overlaid on a GOES-EAST Visible/Infrared image captured at 1645 UTC (11:45 AM CDT). GPM's Dual-Frequency Precipitation Radar (DPR) instrument scanned along an area east of Patricia's center of circulation. Due to Patricia's poor organization the approximate location of Patrica's center of circulation is indicated on this image by an engraved red tropical storm symbol. Rain was measured by GMI falling at a rate of over 55 mm (2.16 inches) per hour in storms west of Patrica's center.

Tropical storm Patricia is located in an environment that is favorable for intensification. Light vertical wind shear and warm sea surface temperatures provide favorable conditions for Patricia to strengthen. The National Hurricane Center (NHC) predicts that Patricia will become a hurricane within 36 hours and move toward Mexico's coast.