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Temp-3.4 C
RH19 %
WindN 17 mph
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Hawaiian Islands Synoptic Discussion and Guidance

460
FXHW60 PHFO 020728 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
928 PM HST Mon Mar 1 2021

.SYNOPSIS...
Windy trade winds will persist through Tuesday before trending
down to locally strong by Wednesday night. A new high pressure
system will usher moderate to strong trades across the region
during the second half of the week, and continue into the weekend.
A wet trade wind pattern is expected Thursday night into the
weekend with the aid of another upper level disturbance.

&&

.DISCUSSION...
There will be a series of surface high replacing one another
through the rest of the week. Currently, a 1040 mb surface high
is about 1000 miles north of Kauai. It is in the process of being
reinforced by strengthening surface high to the west. This new
high will be drifting southeastward Tuesday through Friday,
weakening from 1044 mb Tuesday to 1033 mb Thursday night. On
Friday this high will be replace by a new 1040mb high located
further north. This 1040 mb high will move southeast to 1300
miles northeast of Kauai by Sunday night.

As a result, expect the windy trades to scale down to locally
strong over the east end of the island chain by Wednesday night.
During the second half of the week, with the new high, moderate to
strong trades will settle in over the Kauai end of the island
chain, then gradually expand eastward to rest of the region by
Friday night. Breezy trade will continue into the weekend, with
further strengthening expected, possibly leading to another round
of Wind Advisory over land.

In the mean time, the current Wind Advisory (WA) for most the
islands will expire at 6 am HST Tuesday. Models are indicating for
this condition to continue through Tuesday. Therefore, this WA
has just been extended, and is good til 6 pm HST Tuesday afternoon.

We were just alerted to strong winds atop Mauna Kea. We will be
monitoring the data there closely. Should the strong winds
persist, a Wind Advisory will be issued for the Big Island summits.

It is much quieter night compared to the past few nights, especially
over the eastern part of the island chain, thanks to a stable and
or drier air mass. Satellite imagery and radar depicts a widely
scattered field of low clouds and showers riding in with the windy
trades. These mainly light showers will continue to favor the
windward and mountain areas. Rainfall amounts are light across the
smaller islands, and a bit more over the north and east Big Island
with most locations coming in at less than two tenths of an inch.
The Kona slopes had a flare up this afternoon, but is mostly quiet
now. Radar is indicating an isolated showers just off Captain Cook.

Forecast models point to more stable and drier conditions for
Tuesday. Stable enough where afternoon showers will be isolated at
best for the Kona slopes. We had a layer of dense cirrus clouds
today, but should be thinning out later tonight.

Models are suggesting a series of band of clouds/showers to
descend onto the islands Tuesday night and Wednesday, giving a
boost in trade showers.

Then on Thursday night and Friday/Saturday time frame, we expect
the remnants of an old front to settle over the islands. And this
moisture will be enhanced by another upper level disturbance. So
we are looking at yet another wet period. This wet and windy period
may linger through Sunday.

&&

.AVIATION...
Strong trade winds will continue to be supported by a surface
high to the N, delivering stable and showery low clouds that will
focus over windward slopes and coasts, resulting in periods of
MVFR VIS/CIG. AIRMET Tango remains in effect for moderate to
severe low-level turbulence near and downwind of the terrain, for
locally strong surface winds, and for moderate mid-level
turbulence between FL220 and FL300. Little change is expected
overnight.

&&

.MARINE...
Strong to locally gale force trade winds continue as strong high
pressure holds far north of the state. A Gale Warning is in effect
for the typical windier waters around the Big Island and Maui
County, and is in effect to until 6 pm HST Tuesday. A Small Craft
Advisory (SCA) remains posted for the remaining waters due to the
combination of both strong trade winds and elevated seas.
The surface high will weaken and be replaced by another surface
high far northwest of the islands on Tuesday and this be commence
a short- lived downward trend in the trades. The Gale Warning will
be replaced by an SCA, while the remaing waters continues through
Tuesday night. This long running SCA may be briefly dropped by
Wednesday night as winds and seas decline to borderline SCA
thresholds. Building high pressure to the northwest of the state
will strengthen late week trades and hoist the SCA back up for
more western waters by Thursday. There is a good chance that the
advisory will expand east and hold into the weekend.

Large trade wind-driven seas will maintain high surf along east
facing shores into Wednesday. Nearshore buoys have been holding at
10 to 12 feet with near 10 to 11 second periods. Fully-developed
seas will continue to produce rough east shoreline surf well
above the 8 foot High Surf Advisory (HSA) threshold into Tuesday.
As trade winds over and upstream of the islands weaken, east-facing
shore surf will decline to borderline HSA levels Wednesday with
the HSA likely being dropped by Thursday. Expect east shore surf
to be just below HSA levels late this week and during the weekend.

Surf will remain below advisory levels on all other shores through
much of the week. Exposed sections of both north and south-facing
shores will pull in some trade wind swell wrap and keep south shore
surf near winter averages into Tuesday to then be followed by a
decline late Tuesday and Wednesday. Moderate height, long period
northwest swells begin arriving late Wednesday, peak surf Friday
and then shift out of the north and slowly decline during the
weekend. The bulk of these swells will pass just east of the state
although north-facing shore surf on some islands may reach HSA
levels Friday and Saturday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST Tuesday for 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 Tuesday 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 Tuesday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 PM HST Tuesday 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.


&&

$$
H Lau/Birchard/Blood

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