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Hawaiian Islands Synoptic Discussion and Guidance

456
FXHW60 PHFO 210633
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
833 PM HST Thu Feb 20 2020

.SYNOPSIS...
The strong surface high responsible for the gusty trades will
continue to move east, further away from the islands, resulting
in diminishing trades into Saturday. Showers could be on the
decline as the trades weaken. An approaching front will cause the
trades to turn light and variable area-wide Saturday night, and a
bit of southwesterlies on Sunday. The front stalls and weakens near
Kauai Monday, allowing the return of light trades.

&&

.DISCUSSION...
The surface high responsible for the strong and gusty trade winds
is some 920 miles north-northeast of the islands this evening. It
is heading east at 15 to 20 mph, and this action will result in
continuing diminishing trades. The island-wide wind advisory has
been scaled back to the eastern islands and is only good for this
overnight period. We do not expect an extension of this wind
advisory into Friday at this time.

Between now and Saturday, shower bearing clouds will continue to
ride in with the trades, favoring the windward and mountain areas.
These showers are expected to be trending less, in tandem with
the weakening trades as we enter Saturday. A front will be
approaching the islands from the west bringing on a light and
variable winds regime to most islands Saturday night.

Both GFS and the ECMWF solutions have a front a couple hundred
miles west of Kauai Sunday afternoon, with the islands under a
light west to southwest wind flow. The GFS also shows a strong
low level inversion at 8k feet Sunday afternoon area-wide that
should maintain a mostly dry pattern.

The front stalls and gradually dissipates just north and west of
Kauai Monday. In doing so, light trades start returning on
Monday, and strengthen to moderate speeds Monday night. But as the
front falls apart, some of its remnants may affect Kauai and
Oahu.

&&

.AVIATION...
AIRMET Tango remains in effect for tempo moderate low level
turbulence over and downwind of the terrain due to the breezy
trades. Stable stratocumulus clouds with isolated showers tracking
in with the trades and could bring occasional MVFR ceilings
across windward slopes/waters. Leeward areas should remain mostly
clear to partly cloudy.

&&

.MARINE...
A strong high is moving steadily east to the far north of the
state with a very tight pressure gradient south of it. This is
producing strong to near-gale force easterly trade winds over
Hawaiian waters. A Small Craft Advisory (SCA) remains in effect
through tonight for all Hawaiian waters, but will likely be
scaled back tomorrow to include fewer areas as winds and seas
slowly diminish.

As the high moves farther away to the east this weekend and a
front approaches the state from the northwest, winds will begin
shifting out of the east-southeast and weaken. The front is
expected to move into the far northwest Hawaiian offshore waters
Sunday, with increasing northeasterly trade winds returning behind
the front.

A High Surf Advisory remains in effect through Friday afternoon
for east facing shores of the islands due to the strong trade
winds maintaining rough elevated surf. This surf will subside over
the weekend as the trades weaken.

The current small northwest swell will gradually lower tonight
through Friday. A slightly larger, long-period northwest swell
arriving late Friday will likely peak on Saturday, then gradually
lower Sunday through Monday. A large northwest swell is possible
early next week. Elsewhere, a series of small south and south-
southwest swells will maintain small background surf along south
facing shores through this weekend.

&&


.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Friday for Kauai Windward-Oahu
Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Wind Advisory until 6 AM HST Friday for Lanai-Kahoolawe-Maui
Windward West-Maui Leeward West-Maui Central Valley-Windward
Haleakala-Leeward Haleakala-South Big Island-Big Island North
and East-Kohala-Big Island Interior.

Small Craft Advisory until 6 AM HST Friday for all Hawaiian
waters-


&&

$$


H Lau/Morrison/Powell

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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