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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 220146

Area Forecast Discussion
National Weather Service Honolulu HI
346 PM HST Mon Oct 21 2019

A strong ridge to the north and a trough to the south will
maintain locally breezy easterly trade winds over the area for
the next couple of days. The trades will focus winds over mainly
windward areas. Winds will weaken from mid-week through the
weekend as a couple of fronts approach from the northwest.


The 2 PM surface analysis shows a rather strong 1028 mb surface
high far northeast of the islands near 37N 135W. A ridge extends
southwest from the high to about 500 miles north of the area. This
ridge will maintain locally breezy easterly trade winds over the
area through tomorrow night.A southeast to northwest band of
showery low clouds That moved over the Big Island this morning is
moving away to the west southwest. Some clouds from the band
remain over the Big Island. These clouds and showers will continue
to subside this evening. Partly cloudy skies prevail elsewhere
over the islands. Radars show only isolated showers moving toward
the islands from the east.

The ridge north of the area is forecast to erode over the second
half of the week as a pair of fronts approach from the northwest.
The fronts are expected to stall well northwest of the islands,
but trade winds will weaken as the ridge erodes. The trade winds
will continue to carry some clouds and showers over windward
areas, but rainfall should generally be light. An area of moisture
associated with a tropical disturbance southeast of the islands
could spread north far enough to bring an increase in showers to
the Big Island over the weekend, but this is still uncertain.


Trade winds will focus low clouds and showers across windward
sides of the islands. MVFR ceilings and mountain obscurations may
briefly occur within passing showers over these areas, but VFR
conditions will prevail.

Trade winds will maintain moderate to fresh strength through
Tuesday night before weakening. AIRMET Tango has been posted for
tempo moderate turbulence leeward of all islands due the breezy


High pressure centered far northeast of the state will maintain
fresh to locally strong trades through around midweek. A Small
Craft Advisory (SCA) is in effect for the windy areas around Maui
County and the Big Island through early Wednesday morning. By
mid-week, a front passing north of the islands is expected to
weaken the pressure gradient and will likely cause the winds to
drop below SCA levels across the area. Winds may return to SCA
levels sometime over the weekend as the high far northeast of the
state strengthens.

Surf will remain small along all shores on Tuesday. A small bump
is expected on Wednesday followed by a moderate northwest swell Friday
and Saturday. These swells are expected to stay below advisory
levels along north and west facing shores.

Later this week, a storm-force low is expected develop near
45N170E and track east for a few days. Models are currently
indicating a wide fetch of strong gales within Hawaii's swell
window centered around 320 degrees. If this solution were to
happen, we could see our first solid swell of the season along
north and west facing shores as early as next Sunday with surf
rising well above the advisory levels.

Trade winds will push short-period wind waves onto east facing
shores for at least the next couple of days, trending down later
in the week as trades weaken. The small south swell that filled in
over the weekend is on its way down. Only small surf is expected
along south facing shores for rest of this week.


Small Craft Advisory until 6 AM Wednesday for Maalaea Bay, the
Pailolo and Alenuihaha Channels and waters south of the Big



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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