Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 211328

Area Forecast Discussion
National Weather Service Honolulu HI
328 AM HST Fri Oct 21 2016

Breezy trade winds will persist through the weekend and will
supply periods of wet weather to the area. Trades will focus most
of the shower activity across windward and mauka areas, but some
of the showers will carry over to leeward sides of the smaller
islands. A drier airmass will move into the region next week,
bringing more typical trade wind weather back into the area.


Currently at the surface, a 1032 mb high is centered around 950
miles north of Kauai, and is driving the breezy trade winds across
the island chain. Infrared satellite imagery shows partly to
mostly cloudy skies in place across most of the state, with the
more extensive cloud cover in windward areas. Meanwhile, radar
imagery shows numerous showers moving into windward areas, with
some of the showers reaching leeward areas of the smaller
islands. Main short term concern for today revolves around rain

Strong high pressure north of the state will keep a breezy to
locally windy trade wind flow in place across the island chain.
Mimic total precipitable water (PW) imagery shows an area of
enhanced moisture with PW values between 1.4 and 1.7 inches over
and upstream of the islands, and this should result in fairly
widespread shower activity across windward and mauka areas through
the morning hours. By afternoon, some slightly drier air will
begin to work into the Big Island, so we should see a decrease in
windward showers here, while daytime heating allows for scattered
shower development in Leeward areas. Across the smaller islands,
the deeper moisture is expected to hang around through the day,
keep a wet trade wind pattern in place for windward locales. Given
the strength of the trades, some of the showers will make it into
leeward sections of the smaller islands through the day as well.

Tonight through Sunday night,
High pressure north of the state will keep a breezy to windy
trade wind flow in place through the period, particularly on
Saturday when a wind advisory may be needed for portions of the
island chain. Areas of enhanced moisture will move in with the
trades through the period, bringing periodic increases in shower
activity. Another band of deep moisture will move through the
area tonight keeping a wet trade wind pattern in place across the
area. A slightly drier and more typical trade wind regime will
resume on Saturday and Saturday night, followed by a band of
deeper moisture associated with an old front moving through the
islands Sunday and Sunday night. Showers will favor windward and
mauka areas through the period, with showers reaching leeward
areas of the smaller islands as well due to the strong trades,
particularly during the overnight and early morning hours.

Monday through Thursday,
High pressure will weaken north of the state during the early to
mid week time frame, allowing the trade winds to ease to moderate
levels. The trades will then strengthen by late next week as
another strong high builds well north of the Aloha state. As for
sensible weather details, a typical trade wind weather regime is
expected through the period, with a slight increase in showers
possible on Wednesday as a weak frontal boundary pushes southward
through the island chain. Showers will continue to favor windward
and mauka areas, with an occasional shower spilling over into
leeward areas of the smaller islands.


The strong low level trade wind flow will continue to transport
low clouds and showers mainly over the windward facing slopes and
higher terrain on most islands. This will likely produce periods
of MVFR conditions due to lower ceilings and reduced visibilities.
A few showers may be carried over to leeward sections of some of
the smaller islands due to the breezy trades, especially this
morning and later tonight. Otherwise, VFR conditions will

AIRMET SIERRA has been issued for Mountain Obscuration for the
northeast facing slopes along windward Big Island and Maui. This
AIRMET will likely continue for these areas until around mid-
morning. Additional islands may need to be added to this AIRMET
later this morning.

AIRMET TANGO remains in effect for tempo moderate low level
turbulence leeward of the mountains on all islands. This AIRMET
will likely be required through the upcoming weekend as the
breezy low level trade wind flow continues.


A Small Craft Advisory (SCA) covers all coastal waters through
Sunday due to the strong trade winds. Winds are forecast to reach
near-gale strength in the typically windy areas around the Big
Island and Maui today through Sunday. The trades will start
decreasing Sunday night with the areas under the SCA likely being
scaled back to the typically windy waters early next week.

There will be a series of mainly small northwest to north
northwest swells into next week, and a small background swell
from the south. The strong trades, along with the upstream fetch,
will build surf for east facing shores beginning today. Surf
heights are likely to reach advisory levels over the weekend, and
a High Surf Advisory will likely be issued for east facing shores
later today or tonight.


Small Craft Advisory until 6 PM HST Sunday for all Hawaiian



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