Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
824 AM EDT Thu Oct 26 2017

Valid 00Z Fri Oct 27 2017 - 00Z Fri Nov 03 2017

At the start of the period, a shortwave trough to the north was
seen exiting the region with frontal showers gradually coming to
an end across the Big Island. While the system does cut off
generally between 150-140W longitude, it should remain far enough
to keep primary impacts away from Hawai`i. The 00Z UKMET was a
notable outlier being decidedly west of the consensus. Eventually
a much stronger band of height falls cross the International
Dateline this weekend with the resultant closed low off to the
northwest of the state by Tuesday. The guidance vary considerably
with this feature as the 06Z GFS sped up well ahead of the 00Z run
which was on the far western side of the spread. Currently, the
06Z GFS only has the 00Z CMC as a comparable solution. Ensemble
spaghetti plots are scattered across the board suggesting a below
average confidence forecast in play moving into next week. Given
the system does close off, would prefer to stay on the slower side
of the envelope which suggests the 06Z GFS is too quick.

In the wake of a shearing frontal zone, light north-northwesterly
flow is noted although some residual high precipitable water air
lingers over the Big Island which keeps scattered showers in the
forecast. Models shows a weak shear axis remains over the southern
most islands into the weekend. By early next week, light warm
advection starts to take shape with 5 to 10 knot
south-southeasterly flow ensuing over much of the region. A
resultant increase in moisture will enhance the coverage of shower
activity into early next week as a cold front approaches from the
northwest. The 00Z ECMWF does show the boundary reaching Kauai by
the middle of next week which would bring more organized rainfall
to the region. However, too much uncertainty exists at this time
given the myriad of frontal placements noted.


Rubin-Oster