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Hawaiian Islands Synoptic Discussion and Guidance

751
FXHW60 PHFO 251932
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
932 AM HST Thu Feb 25 2021

.SYNOPSIS...
Breezy to locally windy trade winds will continue into next week.
Showers will remain focused over windward slopes, but a
disturbance aloft will enhance shower activity Friday through the
weekend.

&&

.DISCUSSION...
An exceptionally strong 1046 mb surface high centered about 1500
miles north of the state is driving strong easterly trade winds.
A Wind Advisory remains posted for portions of the Big Island and
Maui, where wind gusts around 50 mph are expected over and
downwind of terrain. A narrow upper level trough is building over
the area from the east, eroding the inversion and leading to some
instability. As a result, few heavy showers are flaring this
morning within a band of moisture moving onto windward Big Island
and Maui and skirting just north of the other islands. Expect an
uptick in mainly windward rainfall as this band moves through
today, though a few showers will spread over leeward areas on the
gusty trades. There is also enough instability to produce an
isolated thunderstorm on the leeward Big Island slopes this
afternoon.

Winds will ease slightly on Friday and the weekend, while
instability leads to periods of active showers. The high to the
north will weaken and be displaced by another surface high
approaching from the west Pacific. Trades will weaken slightly as
early as Friday, creating border line Wind Advisory conditions
for the Big Island and Maui, and trades will decline to locally
breezy strength during the weekend. The upper level trough will
settle over the state, essentially wiping out the inversion and
producing instability. As a result, expect pockets of moisture
moving in the trade wind flow to become enhanced, and deeper
moisture developing near the Big Island and Maui could produce
more widespread heavy showers and a few thunderstorms.

The current run of breezy trades will persist into early next
week. High pressure will dominate far north of the state, but the
GFS and ECMWF differ on some important details. The GFS shows the
upper level trough overhead weakening, while the ECMWF suggests
that this feature will be reinvigorated, leading to weaker trades
and higher chances for enhanced shower activity. For now, the
forecast favors the GFS.

&&

.AVIATION...
Strong high pressure far north of the state is producing strong
easterly trade winds across the area. AIRMET Tango remains in
effect for low level mechanical turbulence for areas over and
immediately south through west of mountains. This AIRMET will
continue into the overnight hours.

VFR conditions prevail across most of the area with brief periods
of MVFR conditions over some windward locations in low clouds and
showers. Expect these conditions to continue on into the evening
hours.

&&

.MARINE...
Strong high pressure NE and N of the islands will maintain strong
to near gale force trade winds over and upstream of the islands
into next week. A Small Craft Advisory (SCA) for all waters has
been extended through the weekend as winds and/or seas will continue
to meet criteria, and an ongoing Gale Warning for the Alenuihaha
Channel is in place through tonight. A subtle decrease in wind
speeds from Friday into the weekend may allow the Gale Warning to
be dropped. Winds may increase again early next week as a new high
builds N of the area.

The strong trade winds extend well upstream of the islands, and
are driving a well-developed (10-11 second period) wind swell toward
the islands from the E. A High Surf Advisory for E facing shores
will remain posted for the next several days. Elsewhere, surf will
be below advisory levels, but several long-period NW swells are
expected over the next week. Peaks in these swells can generally
be expected tonight and Friday, Saturday night/Sunday, and
Wednesday/Thursday, with the last swell expected to be the largest
of the three.

Some trade wind swell will wrap into exposed shores/reefs along N
and S facing shores, and a small long-period S swell is also
expected the next couple of days.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Monday 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 PM HST this evening for Molokai-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 PM HST Sunday 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-Maalaea Bay-
Pailolo Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

Gale Warning until 6 AM HST Friday for Alenuihaha Channel.

&&

$$

DISCUSSION...Wroe
AVIATION...Burke
MARINE...Birchard

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



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