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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 270150

Area Forecast Discussion
National Weather Service Honolulu HI
350 PM HST Wed Oct 26 2016

Trade winds will persist across the main Hawaiian Islands through
the forecast period, becoming stronger Thursday through early next
week due to building high pressure to our north. A weak frontal
cloud band expected to pass across the islands tonight and will
bring an increase in clouds and showers. A shortwave over the
state will bring a progressively wet trade wind weather pattern
this weekend and Monday.


A ridge of high pressure far north of the state is driving moderate
to fresh trade winds across Hawaii late this afternoon. Visible
satellite shows a band of clouds associated with a weak cold front
moving onto the island chain at this time. We have already seen an
increase in clouds and showers from Kauai to Maui earlier this
afternoon. The front will continue to impact these areas tonight
as well as extend to the Big Island tonight. The front is fairly
shallow and moving relatively quickly, so rainfall intensity and
accumulation amounts are expected to be on the light to moderate
side. The trade winds will focus showers across windward and mauka
areas, but will occasionally pass to leeward sides of the islands at
times tonight. The front will move southwestward tonight and should
be clear of the island chain Thursday morning. Anticipating more
sunshine across the area by tomorrow afternoon.

The high pressure system far to the northwest will build east
southeastward over the next several days. As this occurs, we
expect stronger trade winds to dominate across the state from
Thursday night through early next week. Upper level ridging will
keep a cap on showers Thursday night through Friday afternoon,
with only light rainfall amounts expected within trade showers.

An upper level shortwave is expected to pass just northeast of
the island chain Friday night, followed by a second wave Sunday
and Monday. Models show these disturbances enhancing the low
level showers carrying in with the trade winds, which translates
to a progressively wet trade wind weather pattern from Friday
night into early next week. The stronger than average trade winds
will ensure many of the leeward sides of the islands will get some
rainfall at times.

The midlevel ridge begins to build back in around Tuesday of next
week while the moisture slides west of the state, resulting in a
drier weather pattern. Meanwhile, the high pressure to the north
will weaken, which will also weaken the trade winds back to
moderate levels.


A shallow band of moisture moving along a rather stable trade wind
flow will move over the islands through the first part of tonight,
bringing widespread MVFR ceilings to windward slopes. AIRMET
Sierra for mountain obscuration is in effect from Kauai to Maui
and will be extended to cover windward Big Island by nightfall.
Mountain obscuration is expected to diminish over the smaller
islands by around midnight but may linger through the night on
the Big Island. VFR conditions will prevail over leeward areas
tonight, and as a drier airmass moves overhead on Thursday, VFR
conditions should dominate statewide.

The stable trade wind flow will increase as the shallow band of
moisture clears most islands late tonight. AIRMET Tango for low
level turbulence to the lee of all islands will likely be issued
tonight and persist beyond Thursday.


Moderate trade winds with locally breezy conditions
will remain through tonight before the trade winds strengthen on
Thursday. A Small Craft Advisory (SCA) is in effect for the
typical windy zones around Maui County and the Big Island through
Thursday, which will likely be expanded to cover additional zones
or all coastal waters Thursday night. Winds will remain fresh to
strong across the waters into early next week.

The current northwest swell will decline tonight. A series of
small to moderate north and northwest swells will fill in this
weekend and again towards the middle of next week, but surf is
expected to remain below advisory levels.

For the south facing shores a small long period swell will bump
surf up slightly today into Friday. A long period east swell is
possible this weekend from the distant Hurricane Seymour in the
Eastern Pacific.


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




Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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