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Hawaiian Islands Synoptic Discussion and Guidance

584
FXHW60 PHFO 011404 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
404 AM HST Mon Mar 1 2021

.SYNOPSIS...
Windy trade winds will persist through Tuesday before a softening
trend begins. This comes about as the strong surface high far north
of Kauai starts weakening Tuesday. A new surface high may usher in
breezy trades to the western part of the region during the second
half of the week. A more stable air mass is forecast to build
over the islands today as the upper level trough weakens and drift
south of the Big Island. A boost in trade wind showers will come
during the second half of the week with a front settling near the
islands, aided by another upper level disturbance.


&&

.DISCUSSION...
The widespread heavy showers that occurred across the northern
section of the Big Island, including the Hilo and Puna districts
during the evening, continues to trend down. There will be
showers moving onshore but they are no where close to what
occurred earlier in the evening. As conditions start to improve,
stars are beginning to appear on the web cams atop Mauna Kea, with
a nice layer of snow on the ground. It is difficult to tell how
deep this layer of snow is, however. The Winter Advisory has been
extended to 10 am HST for the icy and snow covered roads.

Forecast models are suggesting this stable air mass to spread
south across the Big Island through out today, reaching near
South Point this afternoon. So, it is safe to say that the threat
of widespread heavy showers has ended across the flood watch
area, and thus, the Flash Flood Watch for parts of the Big Island
and for windward Maui is canceled. Should there be any flare ups,
they will be short-lived and be dealt with a Flood Advisory.

We are currently seeing a east to west band of scattered showers
cutting through the smaller islands. So, it will be a little bit
showery this morning, but it should be rather nice and drier this
afternoon, especially along the leeward beaches. It will also be
rather windy. The balloon sounding out of Lihue this morning and
weather radar derived winds from south Kauai is showing 30 to 35
knots at 25 hundred feet already. It is also rather windy across
Oahu with winds blowing just below advisory criteria at a couple
of locations. With the trades forecast to strengthen through the
coming hours and peaking this afternoon, the Wind Advisory is
extended to Oahu and Kauai. This Wind Advisory is good to until 6
pm HST this afternoon. Further extension of the advisory is highly
possible, through tonight. The weather system responsible for the
windy trades, a strong 1043 mb surface high, is located 1250
miles north-northeast of Kauai this morning. In the next 24 hours,
this high is forecast to drift south, closer to the islands, but
weakening slightly as well. By Tuesday night, this high will be
taken over by another strong high that will be drifting
southeastward through Thursday. This may bring a shift to the
breezy trades from Maui and the Big Island to the western part of
the island chain.

During the second half of the week, models are in agreement for a
band of showers to move through the islands Wednesday evening.
Wetter conditions moves in Thursday through at least Friday due to
a front settling near the islands from the north. This front will
be aided by an upper level trough.

&&

.AVIATION...
Strong high pressure to the distant N will support very strong
trade winds while a weakening trough aloft keeps the island
atmosphere somewhat unstable in the short term, most notably near
Maui and the Big Island. The recent steady stream of windward
showers is expected to diminish through the day as the trough
aloft slides S of the islands, and incoming moisture diminishes.

AIRMET TANGO for moderate lee turbulence remains posted, and now
includes a mention of isolated areas of severe turbulence. TANGO
also includes mention of localized sustained strong surface winds
of 30 kt. AIRMET SIERRA is posted for mountain obscuration on the
windward slopes of Maui and the Big Island.

&&

.MARINE...
Strong high pressure to the north of the state will produce
areawide strong to local gale force trade winds across our near-
shore waters. Persistent, strong trades over the past several
days have generated fully- developed, rough seas around the
islands and this rough sea state will hold through Tuesday. Trades
achieving or frequently gusting to gale through the windier
channels and bays surrounding Maui County and the Big Island has a
Gale Warning posted for the Pailolo and Alenuihaha Channels,
Maalaea Bay and those waters south of the Big Island. A Small
Craft Advisory (SCA) remains in effect for all of the remaining
coastal waters due to the combination of strong trades and high
seas. These hazardous maritime conditions will persist into
Tuesday as high pressure dominates north of the islands. This high
will be weakened by the passage of a North Pacific cold front
late Tuesday and Wednesday. This will result in a short term
decline in both trades and seas and lead to an anticipated
cancellation of this long running SCA over most, if not all,
coastal waters by Wednesday evening. As high pressure moves in
from the west and travels north of the islands later this week,
trades will restrengthen to moderate to locally strong magnitudes
from late Thursday into the weekend.

Trade wind-driven rough seas will maintain high surf along east-
facing shores for another couple of days. Although east swell is
subtly lowering, these swells in tandem with easterly wind waves
will continue to justify the ongoing High Surf Advisory (HSA) for
the east-facing shores of Kauai, Oahu, Molokai, Maui and the Big
Island. Areawide trades will remain strong to near gale force
magnitudes within the windier channels and bays through Tuesday.
The HSA will be in effect to account for greater than 8 foot surf
heights along most eastern exposures through Tuesday evening or
early Wednesday morning.

Surf will remain below HSA criteria on all other shores through
much of the week. Sunday's small, moderate period northwest
swells are on the decline today and Tuesday. A larger, long period
northwest swell arriving late Wednesday will lift recent well
below average north and west-facing shoreline surf back to near
advisory levels Thursday and Friday. These swells will shift more
north and decline through next weekend. Surf along south-facing
shores will remain at or slightly above winter averages through
Tuesday due to a combination of both small south-southwest swells
and trade wind wave and swell wrap.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST this evening 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.

Winter Weather Advisory until 10 AM HST this morning for Big
Island Summits.

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