Area Forecast Discussion
Issued by NWS Honolulu, HI

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263
FXHW60 PHFO 201755 AAA
AFDHFO

Area Forecast Discussion...UPDATED
National Weather Service Honolulu HI
755 AM HST Mon Nov 20 2017

.SYNOPSIS...
A surface low about 1000 miles northeast of the islands will move
away to the northeast. A surface high far north of the area will
move southeast through Thanksgiving Day, then dissipate. A strong
new surface high will build far northwest of the islands on
Wednesday, then move southeast through early next week. A trough
aloft will remain over the area.

&&

.DISCUSSION...
The pressure gradient between a surface high far north of the area and
a low to the northeast is producing gentle to fresh north winds.
Satellite water-vapor imagery shows a trough aloft extending north
from over the islands. Despite the trough, the atmosphere remains rather
dry and stable. Balloon soundings at 200 AM showed strong temperature
inversions near 8000 feet at Lihue and 7000 feet at Hilo. The
north winds are carrying scattered showers over north sections of
the islands. A few locations on Kauai tend to be rather rainy with
north winds and the rain gage at Kilohana recorded .31 inches overnight.
Rainfall has been quite light elsewhere.

The trough aloft continues to produce strong west winds over the summits
of Mauna Kea and Mauna Loa on the Big Island of Hawaii. A Wind Advisory
is in effect for the summits. The winds are expected to gradually subside
as the trough weakens.

Over the next couple of days, the surface low northeast of the
area will move northeast and weaken while the surface high moves
southeast and weakens. Winds over the islands will shift out
gradually shift out of the northeast. The northeast trade winds
will carry some showers over windward areas, especially during the
nights and mornings, while leeward areas will remain mostly dry.

Starting Wednesday night, a strong new surface high far northwest
of the islands will start moving southeast. The northeast trade
winds over the islands will strengthen and become breezy. Wind
speeds will likely decrease again starting Saturday, but trade winds
will likely persist through at least early next week.

&&

.AVIATION...
VFR conditions will prevail, but showery clouds moving south over
the area will produce brief MVFR ceilings and visibility over
north sections.

AIRMET Tango is in effect for moderate low level turbulence
downwind of the higher terrain of the Big Island. These conditions
will likely remain in place through tonight.

&&

.MARINE...
A High Surf Advisory (HSA) is in effect for north facing shores of
all islands except Lanai due to a large north swell. The Wave
Watch III shows the swell subsiding, but the swell has been higher
than the Wave Watch III forecasts, so the HSA may need to be
extended. A very large north northeast swell is expected to arrive
on Wednesday. A High Surf Warning (HSW) likely be needed as this
swell builds through Thanksgiving Day. The swell will gradually
subside through Saturday. Another large north northeast swell is
expected to arrive on Sunday.

A Small Craft Advisory (SCA) is in effect through this evening for
all Hawaiian waters except Maalaea Bay and waters south of the
Big Island due to seas above the 10 foot SCA threshold. These seas
associated with the large north swell. The swell has been running
higher than forecast by model guidance, so the SCA may need to be
extended.

Winds are expected to remain below the 25 kt SCA threshold through
tomorrow. On Wednesday SCA conditions will likely return. A large
new north northeast swell will boost seas above 10 feet on
Wednesday while winds will strengthen above 25 kt in the windier
areas around the Big Island and Maui Wednesday night. On
Thanksgiving, winds will likely strengthen above 25 kt across most
of the coastal waters and may reach near-gale force in the
windiest areas.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 600 PM today for north facing shores of
Niihau, Kauai, Oahu, Molokai, Maui and the Big Island of Hawaii.

High Wind Advisory until 6 PM today for the summits of Mauna Kea
and Mauna Loa on the Big Island.

Small Craft Advisory until 600 PM today for all coastal waters except
Maalaea Bay and waters south and west of the Big Island.

&&

$$
Donaldson



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