Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 261950
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
950 AM HST Mon Jun 26 2017

.SYNOPSIS...
A trade wind weather 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. Over the
weekend, an upper low is forecast to pass westward just north of
the area with an uptick in shower activity expected.

&&

.DISCUSSION...
At the surface, high pressure is centered far to the north
northeast of the state with a ridge extending from the high to a
position several hundred miles north of the area. Aloft, an upper
low can be seen in water vapor imagery centered a few hundred
miles west of Kauai. The 12Z soundings reflect this scenario with
inversion heights up to around 9500 feet over Lihue and a much
lower inversion of around 5000 feet over Hilo. Early morning
visible satellite imagery shows rather stable low clouds embedded
in the trades east of Maui and The Big Island with slight taller
cumulus cloud elements around Kauai and Oahu. Radar imagery shows
just a few light showers around the area mainly affecting windward
and mauka areas as well as the adjacent coastal waters.

The islands will remain in a trade wind weather pattern over the
next several days with winds speeds generally in the moderate
range. Clouds and passing light showers will continue to affect
windward and mauka areas with most leeward locations remaining
dry.

As we head into the weekend, an upper level low is forecast to
move eastward toward the state. There are some differences between
the GFS and the ECMWF models on the timing of the lows passage.
The ECMWF is a bit faster with the low passing by just north of
the area on Sunday while the GFS is a bit slower with it passing
by just north of the area on Monday. The net result will be for a
less stable airmass in place allowing for an increase in shower
activity especially over windward and mauka areas. Also the trade
winds are expected to become lighter as a weak low level trough
associated with the upper low slackens the pressure gradient
around the area.

&&

.AVIATION...
The high pressure ridge north of the Hawaiian Islands will
strengthen today allowing trade winds across the state to also
strengthen. Stable, stratocumulus clouds with isolated showers
moving in from the east will impact the windward slopes today.

No AIRMETs are in effect at this time. However, AIRMET Tango may
be needed after 22Z for low level moderate turbulence due to the
strengthening winds. As the clouds push in from the east, AIRMET
Sierra will also be possible later today for mountain obscurations
along windward slopes

&&

.MARINE...
Trade winds will strengthen slightly today into tomorrow,
reaching breezy to locally windy levels. A Small Craft Advisory
(SCA) is posted for the typically windier waters around the Big
Island and Maui County through at least Thursday afternoon. It may
need to be expanded to include the windward Maui waters and the
Kaiwi Channel by midweek.

The strengthening trade winds combined with a northeast swell,
from a fetch of gales west Oregon and California, will help bump
surf up along the east facing shores this week. Surf could near
the High Surf Advisory level starting Tuesday. Some of this
northeast swell energy will also likely wrap into exposed north
facing shores across the state early this week.

Small pulses from the southeast through the southwest will
continue to produce near normal summer time surf along south
facing shores through the period. Reinforcing long period south-
southwest swells will generate small to moderate surf along south
facing shores, starting Thursday into the weekend.

Extreme tides that have been observed during the past several
days are gradually trending back toward normal heights early this
week. As a result, flooding impacts along the coast will continue
to slowly diminish during the next couple of days.

&&

.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.

&&

$$

Synopsis/Discussion...Burke
Aviation...Foster
Marine...Eaton



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