(ABOVE) The latest 5 Day Forecast Track from the National Weather Service. Iselle now appears as a Tropical Storm as it hits Hawaii Island.
Hawaii County Civil Defense message (Aug. 7 at 12:08 p.m. HST)
HILO, Hawaii – With only hours remaining before the forces of Iselle are expected to be felt on the bIg Island, the storm weakens but still qualifies as a Category One hurricane at this hour with winds measured at 75 miles per hour.
Iselle continues to gradually weaken. The eye is no longer evident in satellite imagery… And the reconnasiance aircraft found the surface pressure at the center had risen a couple of millibars. Maximum flight level winds on the northeast side of the cyclone were 69 kt…Which suggests maximum surface winds near 60 kt. Other reduction factor techniques were suggesting 60 to 65 kt maximum sustained surface winds. Thus the intensity for this advisory is being lowered to 65 knots…And this could be a little generous. National Weather Service at 11 p.m. HST
The National Weather Service suggests that the storm is moving too quickly for its own good, pushing forward into unfavorable conditions at a faster pace than expected.
Iselle is still located in a region of relatively weak shear between two upper level anticyclones… To its east and west. The hurricane has been moving slightly faster than this weakness… And will start to feel increasing northerly shear over the next 12 hours which will maintain a weakening trend despite gradually increasing sea surface temperatures. Even if Iselle reaches the Big Island as a tropical storm… Significant impacts will still be felt from wind… rain… and surf.National Weather Service at 11 p.m. HST
The Big Island is likely to weaken the storm even further.
Beyond 12 hours… The combination of much stronger northerly shear and interaction with the Big Island terrain is expected to weaken Iselle further. The track guidance showed a little more spread for this cycle… And shifted somewhat to the south beyond 24 hours… Likely due to uncertainties with the intensity of a weaker iselle. The official forecast thus follows a similar trend with a slight southward shift beyond 24 hours. The intensity forecast is lower than the consensus beyond 72 hours when Iselle is expected to interact with an upper level low digging south over the Northwest Hawaiian Islands. There is a good chance iselle will not survive the interaction with this upper trough. National Weather Service at 11 p.m. HST