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Hawaiian Islands Synoptic Discussion and Guidance

393
FXHW60 PHFO 222010
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1010 AM HST Fri Nov 22 2019

.SYNOPSIS...
High pressure far north northeast of the area is allowing for a
rather windy trade wind weather pattern across the state. Clouds
and passing showers are favoring windward and mauka areas with the
winds sufficiently strong enough for some brief passing showers
over some leeward locations. Expect this weather pattern to
continue through Saturday. Winds will gradually become lighter
early next week as a front begins to approach the area from the
northwest. The front is expected to stall just west of the area
around the middle of next week. Some showers can still be expected
at times mainly over windward and mauka areas with some afternoon
showers possible over leeward and interior areas.

&&

.DISCUSSION...
A 1030 mb high is centered about 1500 miles north northeast of
the state. The pressure gradient south of the high is rather tight
resulting in rather breezy to locally windy trade winds across
the area. A Wind Advisory is currently posted for most areas of
the state. Moisture embedded in the trades is allowing for passing
showers over most windward and mauka areas with brief showers
being blown over the some leeward areas at times. Meanwhile, an
upper level low is centered just to the south of Kauai. This has
resulted in a destabilized airmass in place across the area.
Thunderstorms are presently occurring over the waters south of
Kauai. Daytime heating may allow for a few thunderstorms to form
over some land areas today especially over the leeward Big Island
slopes.

The high is expected to drift northward Saturday and Sunday which
should allow for the strong trade winds to gradually diminish to
moderate levels. The upper low is forecast to weaken and move
eastward over the next few days. This should allow for some
stabilization of the airmass over the area. Clouds and passing
showers will continue to favor windward and mauka areas. Daytime
heating will also allow for the continuance for shower
development over the leeward Big Island slopes each afternoon.

As we head into early next week, a broad area of low pressure both
at the surface and aloft will develop far to the northwest of the
area. Meanwhile high pressure will continue to remain far to the
north northeast of the area. The low associated frontal boundary
will be approaching the area from the northwest. This will result
in our trade winds become lighter. The position of the front will
likely cause winds to become southeasterly over the west end of
the island chain.

The global models are in some disagreement on what other impacts
the front may have on our islands weather during the middle of
next week. The GFS shows that moisture associated with the front
may make it Kauai with rainfall chances increasing. The ECMWF on
the other hand shows the front stalling just west of Kauai
limiting its rain impacts. The current forecast leans more toward
the ECMWF solution keeping the majority of the fronts rainfall
just west of the main Hawaiian islands. However model guidance
could change over the next few days and we could see a wetter
scenario setting up for the west end of the state.

&&

.AVIATION...
With robust high pressure far northeast of the area, trade winds
will be breezy to strong over most locales across the state. Areas
of showers will affect much of the island chain as they move
along on the trades, with windward and mauka sections seeing the
most precipitation (and MVFR conditions in lower ceilings and
visibilities).

AIRMET Sierra in effect for mountain obscuration along the north
and east slopes of Kauai, Oahu, Molokai, Maui, and the Big Island
this morning.

AIRMET Tango remains in effect for tempo moderate turbulence over
and immediately south thru west of mountains on all islands below
8000 feet. Another area of moderate turbulence has developed
between FL250 and FL350 due to the subtropical jet stream. Some
aircraft have reported moderate turbulence in both areas.

&&

.MARINE...
Trade winds will peak today and Saturday with speeds reaching
gale force in the windier waters around the Big Island and Maui
County. A Small Craft Advisory remains in effect for the rest of
the waters. Enhanced winds and seas will remain through Saturday
with a slow decline in strength expected Saturday night and
Sunday. The short period east swell will bring advisory level surf
to east facing shores today and through the weekend.

The current northwest swell will continue to slowly decline today.
A reinforcing, moderate northwest swell will begin to fill in
Saturday morning and peak Saturday night, bringing near advisory
level surf for exposed north and west facing shores Saturday night
through Sunday. A smaller northwest swell is expected by the
middle of next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST this evening for Niihau-Kauai-Oahu-
Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-
Maui Central Valley-Windward Haleakala-Leeward Haleakala-South
Big Island-Big Island North and East-Kohala.

High Surf Advisory until 6 PM HST Saturday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Gale Warning until 6 PM HST Saturday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

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

&&

$$

DISCUSSION...Burke
AVIATION...Kinel
MARINE...Kino

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



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