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Eastern Pacific

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Outlook | Discussion

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Central Pacific Discussion


000
FXHW60 PHFO 271312
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
312 AM HST Tue Jun 27 2017

.SYNOPSIS...
A dry trade wind pattern can be expected over the next several
days as high pressure remains far to the north northeast of the
area. Clouds and passing light showers will favor windward and
mauka areas with most leeward locations remaining dry. An upper
low is forecast to pass westward just north of the area late in
the work week and over the upcoming weekend, bringing a more
showery trade wind pattern to the island chain.

&&

.DISCUSSION...
Currently at the surface, a 1030 mb high centered 1700 miles
north-northeast of Honolulu, is driving moderate to locally
breezy trade winds across the island chain early this morning.
Infrared satellite imagery shows partly to mostly cloudy skies in
place across the State, with cloud cover most prevalent in
windward areas. Additionally, there is some jet stream cirrus
streaming toward the islands from the southwest. Radar imagery
shows some very light showers moving into windward areas, with
rain free conditions elsewhere. Main short term concern revolves
around rain chances.

Today through Friday,
A ridge of high pressure will remain to the north and northeast
of the State through the period, keeping a breezy trade wind flow
in place across the island chain. The airmass will remain quite
dry through Thursday, with precipitable water (PW) values
remaining in the 1.0 to 1.2 inch range. PW values will then climb
slightly above normal levels in the 1.3 to 1.5 inch range
Thursday night and Friday, as an upper level low approaches from
the east. As a result, we expect a dry trade wind shower pattern
through Thursday, with showers limited primarily to windward and
mauka areas. The trade showers should increase in coverage and
intensity Thursday night and Friday as the airmass moistens up and
becomes less stable.

Friday night through next Monday,
The GFS and ECMWF both show the trade winds weakening over the
weekend as weak surface troughing develops over the islands in
response to an upper level low north of the State. The trades are
then expected to strengthen early next week as the surface
troughing over the islands breaks down.

Aloft, the model solutions start in fairly good agreement Friday
night, but then diverge with respect to the handling of the upper
level low over the weekend. The GFS pivots the upper low north of
the islands Friday night through Saturday night, with the feature
then stalling out through early next week with a trailing upper
trough lingering over the State. The ECMWF on the other hand,
lifts the upper level low north of the islands Friday night and
Saturday, with the feature then shifting northwest and away from
the islands Saturday night through early next week as upper level
ridging builds in from the east.

Given the model differences, will continue to favor a blended
forecast approach until the details become more clear. As a
result, we expect a fairly moist and somewhat unstable pattern
will keep a showery trade wind regime in place through at least
Saturday night. We will then show a more typical trade wind
weather pattern Sunday through early next week, but this could be
wetter if the GFS is correct or drier if the ECMWF ends up panning
out. Showers will continue to favor windward and mauka areas
through the period, with some afternoon/evening shower development
likely over interior and leeward areas Saturday and Sunday
afternoon, in the weakened trade wind regime.

&&

.AVIATION...
The high pressure ridge north of the Hawaiian Islands will
produce moderate northeast to east trade winds today. AIRMET
Tango remains in effect for tempo low level moderate turbulence
over and south through west of mountain areas.

Tempo cloud ceilings and showers will move over mountain areas
and across north through east sections of all islands with
isolated showers forecast elsewhere. Brief mountain obscurations
are possible along windward mountain slopes and coasts.

&&

.MARINE...
A Small Craft Advisory (SCA) remains in effect due to strong
trade winds over the typically windy waters adjacent to the Big
Island and the islands of Maui County. The SCA, which is
currently in effect through Thursday, will likely need to be
expanded to include the Kaiwi Channel and the Maui County
windward and leeward waters by mid-week. The latest forecast
keeps SCA conditions over the typically windy areas through
Friday, followed by slightly weaker trade winds this weekend.

The locally strong trades combined with a small northeast swell
generated by a fetch of gales west of Oregon and California, will
produce slightly elevated choppy surf along east facing shores
most of this week. However, surf is expected to remain below the
High Surf Advisory criteria along east facing shores. Some of the
northeast swell energy will also likely wrap into exposed north
facing shores across the state. A small short-period northwest
swell is also forecast from Friday into this weekend.

Small pulses of swell energy from the southeast through southwest
will continue to produce near normal summertime surf along south
facing shores into mid-week. Reinforcing long-period south-
southwest and southwest swells will generate a slight bump in
surf heights along south facing shores from Thursday into this
weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Bohlin
MARINE...Houston

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