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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 210630

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Thu Oct 20 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 Monday and
Tuesday, followed by a weak frontal boundary pushing southward
through the state during the middle of next week.


Currently at the surface, a 1033 mb high is centered around 1000
miles north of Kauai, and is driving the breezy trade winds across
the island chain. Infrared satellite imagery shows partly cloudy
skies in place across most of the state, with some cirrus
enhancing cloud cover over Oahu along with some increased cloud
cover in windward areas. Meanwhile, radar imagery shows scattered
to numerous showers moving into windward areas with the trades.
Main short term concern for tonight revolves around rain chances.

Strong high pressure north of the state will keep a breezy 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 around 100 miles
upstream of the islands, and this should result in an increase in
shower activity particularly after midnight. Due to the strength
of the trades, some of the showers will make it into leeward
sections of the smaller islands as well.

Friday through Sunday night,
High pressure north of the state will keep a breezy to windy trade
wind flow in place through the period, particularly Saturday and
Sunday. Areas of enhanced moisture will move in with the trades
through the period, bringing periodic increases in shower
activity. A band of deeper moisture will move through the area
Friday and Friday night bringing wet trades to the islands. A
slightly drier and more typical trade wind regime will build in
for 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 next 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 produce brief 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. Otherwise, VFR
conditions will prevail.

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 expected strong trade winds. Winds are forecast to
reach near-gale strength in the typically windy areas around the
Big Island and Maui Friday through Saturday. The trades will start
decreasing late Sunday with the areas under the SCA being scaled
back to the typically windy areas by Monday or Tuesday.

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 Friday. Surf
heights are likely to reach advisory levels from Friday night
through Saturday night. Will likely be issuing a High Surf
Advisory for east facing shores on Friday.


Small Craft Advisory until 6 PM HST Sunday for all Hawaiian




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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