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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 212011

Area Forecast Discussion
National Weather Service Honolulu HI
1011 AM 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 8 AM surface analysis shows a rather strong 1031 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. The trades are pushing an east
southeast to west northwest band of showery low clouds over the
windward side of the Big Island. The clouds and showers over the
windward Big Island will subside later today as the cloud band
moves off to the west. partly cloudy skies prevail elsewhere over
the islands. Radars show only isolated showers moving toward the
windward sides of Maui and Molokai with dry conditions elsewhere.

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 re-strengthen today, focusing most of the clouds
and shower activity on the windward side of the islands for the
next few days. A band of moisture will impact the windward and
southeast side of the Big Island today and slide south of the area
late tonight. MVFR ceilings, reduced visibility and brief
mountain obscurations will occur within passing showers over these
portions of the Big Island through tonight. AIRMET Sierra is
posted for windward and southeast portions of the Big Island at
this time. Elsewhere, VFR conditions will prevail.

Low level wind shear may occur at PHOG this afternoon due to the
strength of the winds from 100 degrees east.


High pressure centered far northeast of the state will maintain
fresh to locally strong trades through around midweek. The Small
Craft Advisory (SCA) has been updated to include the typical windy
areas around Maui County this 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.

Model guidance is indicating surf rising Wednesday through
Thursday and peaking Friday or Saturday along north facing shores.
There are still some uncertainties with the swell heights as the
swell makes it to local shores. However, with the typical low bias
of these models, it appears surf along north and west facing
shores may reach just below advisory levels late this week.

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 the Hawaii 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. Surf along south facing shores will remain small
through the 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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