Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
818 AM EDT Sat Jun 10 2017

Valid 00Z Sun Jun 11 2017 - 00Z Sun Jun 18 2017

Broad upper ridging exiting to the east will give way to some form
of weakness which pinches off from the belt of westerlies across
the mid-latitudes. This should linger in the vicinity of the
Hawai`ian island chain during the middle of the week. In
particular, some model solutions show a weak/modest mid-level
vorticity center drifting toward Kauai on Wednesday. The 06Z GFS
indicated a quicker westward acceleration of this feature relative
to the slower 00Z ECMWF/CMC. This theme continues through the
remainder of the period which runs into early next weekend. By
17/1200Z, the quicker 06Z GFS brings the upper trough to around
170W longitude while the 00Z ECMWF/CMC are still back over the
Hawai`ian islands.

At the surface, a series of anticyclones to the north will
maintain moderate trade winds throughout much of the forecast. As
the aforementioned upper low takes shape by the middle of next
week, a north/south inverted trough becomes noted in the low-level
wind fields. This will lead to a sharper axis of surface
convergence as the trough proceeds westward. The 06Z GFS/00Z ECMWF
show much more pronounced surface troughing relative to the
flatter solutions. Eventually this will exit to the west with a
return to a general trade wind regime. Regarding precipitation,
the usual windward showers are likely given the prevailing trades
amidst a fairly high precipitable water air mass. The 00Z ECMWF
suggests precipitable water values above 1.50 inches throughout
the forecast. Given the presence of the upper low drifting
westward across the region next week, expect a brief uptick in
shower coverage/intensity, particularly as shown in the 06Z GFS.
This would primarily impact Kauai where the core of the
mid/upper-level energetics should reside. Overall, do believe the
06Z GFS is too quick but do prefer what it shows in terms of
precipitation.


Rubin-Oster