Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
807 AM EDT Tue Sep 15 2015

Valid 00Z Wed Sep 16 2015 - 00Z Wed Sep 23 2015

Seasonal weather pattern expected for the this 7-day forecast
period.

A generic 15/00Z ECENS/GEFS blend should suffice for day 4-7 and
both deterministic pieces of guidance would support the current
Hawai'i forecast through Friday night (local time).

At the surface---the 15/00Z model guidance maintain a subtropical
ridge and central high pressure center (1023mb) invof 36N146W this
weekend---then the deterministic 15/00Z ECMWF/GFS begin to diverge
with the lat/long positioning and strength of the central surface
high on Sunday (day 5). Much of the difference results from the
variance over the Gulf of Alaska and the mid-latitude solution
downstream.

Aloft---the deterministic ECMWF/GFS solutions reasonably depict
the formation---and then westward migration (between 140W and
160W)--- of a TUTT cell along 25N through this weekend. Though the
bulk of the vorticity associated with the mid-level feature
remains north of the forecast area---it will inherently maintain a
'convective nature' with plenty of shear and isolated thunderstorm
potential---as it passes to the north from east to west.

Vojtesak