Tropical storm Darby has caused some heavy rainfall in the Hawaiian Islands since hitting the big island (Hawaii) on Saturday July 23, 2016. After hitting the big island Darby passed to the south of Molokai and Maui. Rain falling at a rate of 25.4 mm (1 inch) to 50.8 mm (2 inches) per hour was reported on the island of Oahu as Darby passed to the southwest of the island. The National Weather Service office in Honolulu reported that parts of Interstate H-1 that serves the southern side of Oahu was closed due to flooding on Sunday night. Darby is affecting northern Kaui today.

The GPM core observatory satellite had an excellent view of tropical storm Darby as it was approaching Hawaii on July 23, 2016 at 1146 UTC. Rainfall was examined in tropical storm Darby by GPM's Microwave Imager (GMI) and Dual-Frequency Precipitation Radar (DPR) instruments. Those instruments found that a line of intense storms southeast of the big island of Hawaii was dropping rain at a rate of over 136 mm (5.4 inches) per hour.

GPM's Radar (DPR Ku Band) measured the 3-D vertical structure of rainfall within tropical storm Darby. DPR found storm top heights of over 13 km (8.1 miles) in areas of the tropical storm. GPM's discovery of 48 dBZ radar reflectivity values in some downpours provided further evidence of intense precipitation within Darby.