(ABOVE) The latest 5 Day Forecast Track from the National Weather Service
Hawaii County Civil Defense message (Aug. 6, 2014 at 7:15 a.m. HST)
UPDATE: Hawaii Island is now under a Tropical Storm Warning.
HILO, Hawaii – A Tropical Storm Watch is now in effect for the Big Island, Maui and Oahu. Hurricane Iselle is 720 miles east southeast of Hilo. Maximum sustained winds near 85 miles per hour make Iselle a Category 1 hurricane. Additional weakening is forecast through Thursday, and Iselle is expected to be a tropical storm later today or tonight. The storm is moving toward the west-northwest near 15 mph. Iselle is expected to hold that path through Thursday night, with a gradual increase in forward speed. The outer winds of Iselle may reach the easternmost Hawaiian islands by Thursday afternoon. Tropical storm force winds extend outward up to 140 miles.
High surf is expected due to the storm. Swells generated by Iselle will reach the main Hawaiian islands today, possibly becoming damaging along some coastlines starting late tonight or Thursday. Then, heavy rains associated with the storm are expected to reach the Big Island Thursday and spread to the remainder of the state Thursday night and Friday. The National Weather Service warns these rains could cause life-threatening flash floods and mud slides.
Here is the latest discussion on Iselle from the National Weather Service:
The latest satellite images continue to show Iselle is encountering hostile conditions. There is now abundant dry air being entrained into the Iselle. This dry air combined with the adverse vertical wind shear the system encountered Tuesday have resulted in rapid weakening of the once powerful tropical cyclone. The vertical wind shear has decreased during the past several hours… And is now from the north at less than 10 kt based on the latest uw-cimss analysis and ships guidance. Dvorak current intensity estimates are 4.0 from sab… Jtwc and hfo. As a result… The initial intensity has been reduced to 75 kt… Which may be generous at this time. The current motion is 285/13 kt… Which reflects the acceleration of the system south of a subtropical ridge to the north.
The spread of the dynamical and consensus track guidance is slightly greater now compared with 6 hours ago. The latest track forecast for Iselle follows the previous one with only minor adjustments through day 4. Some additional acceleration is forecast later today… Followed by some slowing in the forward motion starting during the 36 to 48 hour period as the system becomes increasingly shallow. Note that the track on day 5 has been shifted to the right… Since most of the models show a more northwestward motion. On this forecast track… The winds from Iselle are expected to affect portions of the main Hawaiian Islands from Thursday through Friday or Friday night.
The current relaxation of the vertical wind shear occurred as an upper level trough west of the hurricane weakened… And a ridge aloft north of the system was building westward. The latest intensity forecast is close to the previous… Which follows the trends depicted by the ships/lgem/ivcn guidance. Steady weakening is expected through the next 3 days… With a slower rate of weakening or steady state thereafter.
It is important for people in the main Hawaiian Islands not to focus too closely on the exact forecast track of Iselle. With an average 48 hour track error of approximately 80 miles… It is still too soon to say with much certainty which islands would be most likely to experience the worst weather… And everyone should be prepared for the possibility of direct impacts from Iselle. It is also important to keep in mind that significant impacts from tropical cyclones can extend well away from the center… With tropical storm conditions over some of the easternmost islands possible starting Thursday afternoon. National Weather Service at 5 a.m. HST