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Hawaiian Islands Synoptic Discussion and Guidance

429
FXHW60 PHFO 051945
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
945 AM HST Fri Mar 5 2021

.SYNOPSIS...
Breezy trade winds will prevail through the middle of next week as
high pressure remains north of the islands. A somewhat wet trade
wind weather pattern will persist, with windward portions of Kauai
and Oahu seeing more shower activity through Saturday. An
increase in showers, some heavy will spread from east to west over
the state late Sunday and persist into early next week.

&&

.DISCUSSION...
A breezy and slightly unstable trade wind flow is producing wet
conditions, especially on windward Oahu and Kauai. The trades are
being driven by a 1034 mb surface high sitting about 1,000 miles
northwest of Kauai. An upper-level trough creeping southward near
Kauai is generating a swath of high clouds over much of the state
and is producing slightly unstable conditions that have wiped out
the inversion. A band of low-level moisture, remnants of a
dissipated front, is draped across Kauai and Oahu this morning,
and due to the instability, widespread windward showers on these
islands are heavier than normal and will easily carry across
leeward areas today. Low-level moisture decreases east of Oahu,
though windward areas, especially on Maui County, will see active
showers today.

Little change is expected through Saturday. The surface high to
the northwest will be absorbed by another high, but winds will
remain breezy, with the strongest trades remaining along the band
of low-level moisture that will slowly dissipate near Kauai and
Oahu. As a result, expect these islands to continue to experience
greater shower coverage. The upper level trough will settle over
the islands, maintaining instability that will produce briefly
heavy showers. Also, the shield of high clouds will gradually push
south and east of the islands.

Unsettled weather will likely develop for portions of the state
late Sunday and could continue through the middle of next week.
The GFS and ECMWF suggest that the upper-level trough will sharpen
just west of the state and enhance moisture moving in on the trade
wind flow. Unsettled weather could develop over the Big Island as
early as Sunday afternoon then spread to Maui County Sunday
night. Details become elusive for early next week due to subtle
differences between the models, but wet trade wind weather could
prevail into early next week.


&&

.AVIATION...
Moderate to locally breezy trade winds will continue to steer
ragged bands of tropical showers toward windward slopes and
coasts. A deep upper level trough pushing out of the Northeast
Pacific and slowly passing over the islands will further enhance
shower activity. Locally heavy downpours possible Oahu westward
today and statewide tonight. Periods of MVFR CIG and VIS are to
be expected, especially along north and east facing slopes and
coasts. AIRMET Sierra is currently in effect for Kauai, Oahu, and
Molokai. Conditions may spread to Maui and Windward Big Island
tonight.

Bands of high clouds streaming out of the south will limit
daytime heating. Little cumulus development is expected over Big
Island Interior today. Cloudy but VFR conditions should prevail
across Maui and the Big Island through early evening.

&&

.MARINE...
The current Small Craft Advisory (SCA) includes most island waters
due to combined seas above 10 feet and/or winds over 25 knots.
Strengthening high pressure to the north will maintain trade
winds at fresh to strong levels into next week.

A north swell will elevate surf heights to near advisory levels
into Saturday before slowly diminishing Sunday. This north swell
may produces surges in north facing harbors, including Hilo and
Kahului harbors. A bump in east shoreline surf will occur over
the weekend as the trade wind swell increases. Surf will likely
reach HSA levels along exposed east facing shores by Tuesday.
Background south swells will provide small surf to south facing
shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Saturday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

&&

$$

DISCUSSION...Wroe
AVIATION...Bedal
MARINE...Morrison

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office



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