Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
830 AM EDT Mon Aug 06 2018

Valid 00Z Tue Aug 07 2018 - 00Z Tue Aug 14 2018

Underneath a broad east/west oriented mid-level subtropical ridge,
Hurricane Hector will continue a westward trajectory, generally
south of 17N latitude the next few days. The forecast cone of
uncertainty now is just south of the Big Island which is a
southward nudge from recent days. However, given the strongest
impacts from Hector would be on its northeastern quadrant, it
would not take much a northward jog to bring impacts to the Big
Island. At the point it crosses the longitude of Hawai`i it will
likely be transitioning from a Category 3 to a Category 2
hurricane. Regarding model guidance, the 00Z UKMET and ensemble
means handle the system most closely to the official CPHC track as
the 00Z CMC is decidedly weaker while the 06Z GFS/00Z ECMWF are a
smidge slow. By the weekend, models show an inverted
mid/upper-level trough migrating westward toward the region. This
ultimately appears tied to an area of disturbed weather
highlighted by NHC with a 60 percent chance for tropical cyclone
development during the next 48 hours. Whatever emerges out of this
should be weakening considerably as it crosses the islands late in
the weekend.

At the surface, a large dome of high pressure across the central
Pacific will encourage a steady period of moderate trade winds,
generally in the 15 to 20 knot range. As Hurricane Hector nears
the region, models show a spike in northeasterly winds, especially
across the Big Island by early Wednesday. the 06Z GFS depicts
surface wind vectors around 40 knots just south of the region so
the track of Hector will need to continue to be monitored. In
addition to the potential for gusty winds, rough seas are likely
given the intensity of the cyclone combined with its brisk forward
motion. While the heaviest rainfall should stay well to the south,
an increase in showers across the Big Island is anticipated as 2
inch plus precipitable water values sweep through. After Hector
exits the region, general trades should return to the picture
although a brief disruption may occur as that inverted trough
crosses through over the weekend. This would be accompanied an
additional threat of organized shower activity.


Rubin-Oster