Tropical Storm Darby moved closer to Hawaii on Friday and the Tropical Storm Watches were upgraded to Tropical Storm Warnings.  At 11:00 p.m. EDT on Friday the center of Tropical Storm Darby was located at latitude 18.7°N and longitude 152.1°W which put it about 205 miles (335 km) east-southeast of Hilo, Hawaii.  Darby was moving toward the west at 12 m.p.h. (19 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 1000 mb.

Tropical Storm Warnings are in effect for Hawaii County and Maui County including Maui, Molokai, Lanai and Kahoolawe,  A Tropical Storm Watch has been issued for Maui.

An Air Force Reserve Hurricane Hunter reconnaissance aircraft investigated Tropical Storm Darby on Friday and provided data from inside the tropical storm.  Darby has an asymmetrical structure.  A primary rainband wraps around the western side of the tropical storm and most of the thunderstorms are west of the center of circulation.  An upper level ridge west of Hawaii is generating northeasterly winds which are blowing over the top of Tropical Storm Darby.  The vertical wind shear caused by the upper level ridge is contributing to the asymmetrical structure of the circulation.  The thunderstorms in the primary rainband are generating some upper level divergence.  Most of the stronger winds are occurring in the northern half of the circulation.

Darby is moving through an environment that is marginal for intensification.  It is moving over water where the Sea Surface Temperature (SST) is near 27.5°C.  However, the vertical wind shear is inhibiting the upper level divergence to the northeast.  The effects of warm SSTs and moderate upper level divergence appear to be offsetting each other and the intensity of Tropical Storm Darby did not change much on Friday.  As Darby moves farther west, the SSTs will start to decrease and the vertical wind shear will increase.  The more hostile environment is expected to cause Darby to weaken during the next few days.

A subtropical ridge north of Darby is steering the tropical storm toward the west.  Darby is moving near the western end of the ridge and it is expected to turn more toward the northwest during the weekend.  On its expected track Tropical Storm Darby is forecast to move near the Big Island of Hawaii on Saturday.  If Darby makes the expected turn toward the northwest, it could affect much of Hawaii.

Tropical Storm Darby will bring strong winds and higher than normal surf to Hawaii.  However, the greatest risk will be caused by winds flowing up slopes, which will produce locally heavy rain and the chance for flash floods.