Tropical Storm Darby moved closed to Hawaii on Thursday and Tropical Storm Watches were issued for some of the islands.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Darby was located at latitude 18.9°N and longitude 147.5°W which put it about 500 miles (800 km) east of Hilo, Hawaii.  Darby was moving toward the west at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 997 mb.

A Tropical Storm Watch has been issued for Hawaii County and Maui County including the islands of Maui, Molokai, Lanai, and Kahoolawe.

Tropical Storm Darby is maintaining its structure.  A primary rainband wraps around the north and west sides of the center of circulation.  Strong thunderstorms continue to develop close to the center of circulation.  Those thunderstorms are producing upper level divergence.  Darby is a small tropical storm.  Winds to tropical storm force extend out about 100 miles (160 km) on the north side of the circulation, but they only extend out about 50 miles (80 km) to south of the center.

Tropical Storm Darby is moving through an environment that is marginal for intensification.  It is moving over water where the Sea Surface Temperature (SST) is near 27°C.  So, there is enough energy in the upper ocean to support a tropical cyclones.  However, an upper level ridge centered west of Hawaii is generating northeasterly winds which are blowing over the western half of the circulation.  The moderate vertical wind shear is inhibiting intensification.  Darby maintained its intensity on Thursday as the positive and negative environmental factors effectively balanced each other out.  Darby could continue to maintain its intensity for several more days until it moves over cooler SSTs and into a region of stronger vertical wind shear.

A subtropical ridge north of Darby is steering the tropical storm toward the west.  That general motion is forecast to continue for another 36 hours.  On its anticipated track Tropical Storm Darby could approach the Big Island of Hawaii in about 36 hours.  It could bring tropical storm force winds to that island.  In addition Darby could cause heavy rain and flash flooding in locations where the wind blows up the slopes on the islands.