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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 050236

Area Forecast Discussion
National Weather Service Honolulu HI
436 PM HST Fri Dec 4 2020

A passing surface high north of the islands will cause the trade
winds to remain rather breezy and gusty through this evening.
Trades will then trend down tonight and Saturday, becoming light
and variable over the western islands by Saturday afternoon. Light
and variable winds will persist into Sunday, then give way to
strengthening trades Monday into Tuesday as a new high pressure
system passes by to our north. Trade winds will become lighter
later in the week as high pressure moves off to the northeast of
the area. Passing light showers will persist when the trades a
blowing with some interior showers possible during the lighter
wind days.


A 1021 mb high is centered a few hundred miles north northeast of
the state. This is providing for moderate to locally breezy trade
winds across the area. Pockets of moisture embedded within the
trades is providing for some brief passing showers over windward
and mauka areas while most leeward locations are generally dry.
These conditions are expected to persist through the evening

The tail end of of a dissipating frontal band may sag south enough
to cause a slight uptick in showers for windward and mauka areas
over the west end of the state later tonight and Saturday

The high will have moved off to a position far northeast of the
area by Saturday with trade winds becoming lighter and veering
toward a more southeastly direction over the west end of the
island chain.

Winds will remain light through the weekend as a front approaches
the areas from the northwest. The front is forecast to stall and
dissipate north of the area Monday and Tuesday. Meanwhile, a new
high will be passing by north of the area with an uptick in trade
winds expected.

By Wednesday, the high will be far northeast of the area while
another front approaches from the northwest. Winds will once
again become lighter favoring southeasterlies over the west end
of the island chain. Models indicate some increase in moisture out
ahead of this front so there may be some increase in shower
activity across some areas.


High pressure far north of the Hawaiian Islands, will produce
increasing trade winds into the moderate to breezy range across
the region today as it moves eastward. Passing showers will focus
mainly over mountains and along north and east facing slopes of
each island through tonight, then dry out Saturday. Trades will
shift out of a more easterly direction and begin to ease tonight
as the remnants of a front approaches from the northwest and
stalls west of Kauai.

AIRMET TANGO is in effect for low-level mechanical turbulence over
and downwind of island terrain for all islands. Conditions
expected through tonight.


A high moving west to east, north of the state will generate
strong trades through tonight. The Small Craft Advisory (SCA) has
been scaled back to only include typical winder waters around
Maui and Big Island through tonight. Trades will drop off over
the weekend, especially over the western end of the state.
However, SCA may need to be updated later this weekend for
building seas.

The large northwest swell that peaked Wednesday will continue
to fade. Wave Watch III is showing another northwest swell moving
down the island chain quickly Saturday that may bring surf along
exposed shores near High Surf Advisory level. Long- period
forerunners from another northwest swell is anticipated to fill in
early Sunday which may drive surf heights along exposed north and
west facing shores well above warning levels (XL category) and
seas above the SCA criteria. This northwest swell should drop
below the advisory levels by midweek.

This long stretch of advisory- to warning-level surf discussed
above will only exacerbate the ongoing coastal erosion issues -
especially with water levels running higher than predicted each
day. The best chance for water to reach vulnerable coastal
properties and roadways will be around and after daybreak Monday
when the peak daily high tide could coincide with the peak of
this next large swell.

Surf along east facing shores will remain small over the weekend,
then trend up slowly next week as the trades fill in locally and
upstream of the islands.

Surf along south facing shores will remain small with mainly a
mix of small, short-period southeast and background south-
southwest energy moving through.


Small Craft Advisory until 6 AM HST Saturday 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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