Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 121402 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
402 AM HST Thu Dec 12 2019

.SYNOPSIS...
Light trade winds and mostly dry weather will prevail today.
Strong high pressure passing north of the islands will bring
increasing trade winds tonight and Friday, with locally breezy
trades persisting into the weekend. The strengthening trade winds
will bring passing clouds and showers to windward portions of the
islands, but a front stalling just northwest of the area will
bring increased rainfall to Kauai and adjacent waters the next
couple of days. High clouds are expected to periodically pass over
the islands starting tonight and persisting through Saturday.

&&

.DISCUSSION...
Have made some modifications to the grids, but no major changes to
the overall forecast. In general the winds have been nudged closer
to the latest GFS solution, but the flavor remains the same with
trade winds increasing starting tonight, and remaining trades into
next week. Modified the PoPs and associated fields for tomorrow to
better align the model solutions across the board. This boosts
PoPS across the area, but didn`t got go as high as many of the
models.

A recent VIIRS day/night band satellite image shows mostly clear
skies over most of the islands, with Oahu have the most clouds
focused over the windward Koolau slopes. Clouds associated with a
front to the northwest of the islands are about 60 miles northwest
of Kauai at 2am.

The latest GFS and ECMWF models continue to show some differences
with an upper level system moving over the islands, however both
bring some instability near the islands tonight and tomorrow.
Thunderstorms are observed just outside the coastal waters to the
southeast of Kauai this morning. The models show the strongest
dynamics for thunderstorms to remain to the southeast where a mid
to upper level low forms along the base of the upper level trough.
Will need to be monitoring the thunderstorm area to see if they
will edge into the coastal waters and Kauai, but at this time have
left them out. The proximity of the system to Kauai will place
them in the greatest chance for enhanced rainfall.

High pressure far northwest of the islands will move to the east
through the weekend, followed by another high early next week.
Both highs will remain north of the islands. The front to the
northwest of the islands will be pushed over the western end of
the coastal waters today, and winds north of the front are
expected to be strong and out of the northeast, while out ahead of
the front moderate easterly trades are expected tonight and
Friday.

As the high mentioned above moves to the east this weekend, the
upper level low will move to the west, and locally breezy trade
winds will spread across the islands. As we transition to the
second high, trade winds could slacken a bit on Sunday, before
rebounding with the second high Monday and Tuesday. With the trade
wind flow over the islands. showers will be focused over windward
areas for the remaining islands.

Mid and upper level ridging moving over the region early next week
will help to stabilize the atmosphere limiting trade winds
showers, however leftover frontal moisture will be riding in on
the trades at times will bring some moisture bands in on the
trades from time to time.

&&

.AVIATION...
With a light east to southeast background flow, early morning land
breezes will give way to developing sea breezes over parts of the
state this afternoon. This will lead to some cloud buildups over
island interiors into the evening. Little in the way of rainfall is
expected due to a stable air mass over the area. VFR will dominate
in most areas. A front approaching from the northwest will begin to
affect Kauai as early as this afternoon, with increasing trade
winds, clouds and showers. Clouds and winds will increase for the
rest of the state by Friday as the front stalls near the Garden
Isle.

&&

.MARINE...
A large northwest swell will maintain surf above warning levels
today and tonight. A High Surf Warning is in effect for north and
west facing shores of Niihau, Kauai, Oahu, and Molokai as well as
for north facing shores of Maui. A high surf advisory is in
effect for the leeward Big Island coast. The surf will peak this
morning and then slowly subside into Saturday. Another northwest
swell may produce advisory level surf early next week.

A full moon high tide early this morning (between 2-6am depending
on location) and the large NW swell will bring the potential of
overwash along coastal areas. As of 3am, the swell is running 2
feet larger than the WW3 predicted values at the Waimea buoy,
reaching over 14 feet. Added to the large swell and full moon
tide, is the fact that tide gauges across the state have been
showing water levels near 6/10 of a foot above predicted values.
All of these factors combined will allow waves to reach higher
along exposed coastlines and over low lying coastal roadways.

A front moving SE over the NW offshore waters will stall tonight
NW of Kauai. A new high will pass north of Kauai tonight and
Friday, driving a boost in northeast winds to near gale force
north of the front. Waters around Kauai will see the strongest
winds tonight and Friday. Strong trades will also develop over
the typically windy coastal waters Friday. As the high continues
eastward, trades will weaken over the western end of the island
chain by Saturday, but the locally strong trades over the eastern
waters will continue through the weekend and into next week.

Surf along east facing shores is currently below the seasonal
average. A boost in the trades today and Friday will lead to
higher surf along east facing shores of all islands, but
especially for Kauai where a High Surf Advisory may be needed for
east facing shores. Some increase in surf is also expected from a
northeast swell entering Hawaiian waters Friday and Saturday. The
trade swell will gradually ease this weekend.

Due to the large northwest swell, a Small Craft Advisory is in
effect for all windward waters as well as the leeward waters of
Kauai and Oahu, including the Kaiwi Channel. This advisory will
also cover the strong northeast winds slated for Kauai County
waters tonight into Friday. A Small Craft Advisory for winds will
likely be issued for waters around Maui County and south of the
Big Island later today. Expect this advisory to continue through
the weekend and into early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Olomana-Molokai-Maui Windward West-Maui Central Valley-
Windward Haleakala.

High Surf Advisory until 6 PM HST this evening for Kona.

Small Craft Advisory until 6 PM HST this evening for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-
Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi
Channel-Maui County Windward Waters-Big Island Windward Waters.

&&

$$


DISCUSSION...M Ballard
AVIATION...TS
MARINE...Morrison


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