Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Mon Jun 12 2017

Valid 00Z Tue Jun 13 2017 - 00Z Tue Jun 20 2017

Mean upper ridging exiting toward the eastern Pacific will give
way to a weakness which has been well advertised for days. This
inverted upper trough is forecast to drift westward in time while
remaining in the vicinity of the Hawai`ian islands through at
least Friday and perhaps into early in the weekend. All solutions
agree on the existence of this particular mid-level weakness,
albeit with different positions and strengths. The 06Z GFS/06Z
GEFS mean/00Z ECMWF all are the most amplified with the 06Z GEFS
mean/00Z ECMWF in general agreement with eventual position by next
Monday. Meanwhile, the 00Z CMC allows the system to linger a bit
longer to the west of Kauai.

At the surface, given a broad anticyclone to the north and east of
Hawai`i, moderate trade winds will dominate the overall pattern,
perhaps sustained at 20 knots based on the latest guidance. This
surface high is forecast to continue moving farther toward the
east and weaken which will lead to a slight weakening in the
low-level winds. Looking farther ahead, models have really backed
off on the north/south inverted surface trough which was
advertised in runs a couple days ago. Thus, expect the
climatological trade wind regime to continue its dominance
throughout the period. Regarding precipitation, mid-week should be
the wettest period as the weakness aloft takes shape and begins to
drift westward. The 00Z CMC/CMC ensemble mean are notably drier
which looks a little odd given the high precipitable water
environment in place. Models keep 1.50 to 1.75 inch precipitable
water values in place through midday Thursday before drier air
intrudes bringing a reduction in the coverage of trade driven
showers thereafter.


Rubin-Oster