Infrared data NASA's Aqua satellite showed that the strongest storms within Tropical Storm Darby were occurring north of the center when it passed overhead.
On July 21, 2016 at 1125 UTC (7:25 a.m. EST) the MODIS or Moderate Resolution Imaging Spectroradiometer instrument aboard NASA's Aqua satellite saw coldest cloud top temperatures between minus 60 and 70 degrees Fahrenheit/ minus 51.2 to minus 56.6 degrees Celsius indicating strong storms remained north of Darby's center. Storms with cloud tops that cold and high in the troposphere have been shown to generate heavy rainfall.
NOAA's Central Pacific Hurricane Center (CPHC) that forecasts tropical cyclones in the Central Pacific Ocean noted today "The satellite cloud pattern around Darby remains well-organized, but the area of cold tops has decreased a bit since last evening. Microwave passes at 1059 and 1156 UTC also showed good banding wrapping from west through south through east through north of the center."
At 5 a.m. HST (11 a.m. EDT/1500 UTC), the center of Tropical Storm Darby was located near latitude 18.9 North, longitude 145.2 West. That's about 645 miles (1,040 km) east of Hilo, Hawaii. Darby is moving toward the west-southwest near 15 mph (24 kph). Darby will gradually turn toward the west with a slight decrease in forward speed over the next 48 hours. Maximum sustained winds are near 65 mph (100 kph) and CPHC expects little change in strength during the next 48 hours.
Although there are no coastal watches or warnings in effect the CPHC cautions that interests in the Hawaiian Islands should monitor the progress of Darby.