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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 111351

Area Forecast Discussion
National Weather Service Honolulu HI
351 AM HST Mon Dec 11 2023

Ridging north of the islands will maintain moderate to locally
breezy trade winds today, with isolated to scattered showers
generally favoring windward and mauka areas. Stronger northeast
trade winds are expected to build across the area Tuesday
afternoon, and then persist through at least Thursday night.
Shower chances will also increase across the islands from west to
east Tuesday though Thursday morning before drier air returns
statewide by Thursday afternoon. A return to more typical trade
wind weather is expected from Friday through the weekend.


No significant changes to the forecast this morning. High
pressure remains far northeast of the islands with a ridge
extending from the high to the northern boundary of the offshore
waters. Moderate to locally breezy trade winds have spread across
the region as a result. CIMSS MIMIC layer precipitable water (PW)
shows precipitable water values have become more uniform across
the islands. This correlates well with the overnight soundings
which show Lihue at 1.40 inches, and Hilo 1.49 inches of PW. Much
drier air is noted further northwest near Kauai closer to the
ridge axis.

Moderate to locally breezy trade winds are expected to continue
today, with showers favoring the windward and mauka areas. Expect
drier air to spread over the eastern end of the state later today.

As a front passes north of the islands on Tuesday, moisture will
once again increase over and upstream of the islands. Strong post-
frontal high pressure will also begin to increase winds to
locally strong levels by Tuesday afternoon, and these locally
strong winds will persist through at least Thursday night. As the
high pressure strengthens north of the state, moisture associated
with another front will be pushed down the island chain,
increasing shower chances from west to east Tuesday night through
Thursday morning.

Much drier air will fill in across the state from west to east on
Thursday. More typical trade wind weather with moderate to
locally breezy trades and showers favoring windward and mauka
locations will return from Friday through the weekend.


Moderate to locally breezy trades will continue through the next
24 hours, with only a temporary diurnal weakening across the state
during the overnight hours. Low clouds and showers will cause
windward Big Island to continue to experience MVFR conditions
early this morning, with only brief periods of MVFR conditions
expected across other windward areas. Otherwise, VFR conditions
will prevail.

AIRMET Sierra for mountain obscuration across windward Big Island
remains in effect early this evening. However, drier air has
filtered in and allowed conditions to improve slightly, so this
AIRMET might be dropped later this morning. Satellite imagery,
radar and surface observations show some low clouds and showers
beginning to persist over windward Oahu this morning and if this
activity becomes more extensive, windward Oahu may need to be
included in the AIRMET Sierra for mountain obscuration.


A surface ridge sitting nearly 250 nm north of Kauai will
maintain moderate to locally strong trade winds through today. A
Small Craft Advisory (SCA) is in place for the typically windy
waters around the Big Island and Maui. Winds should ease slightly
and become northeasterly around Kauai this afternoon and evening
as a front approaches from the northwest followed closely by a
strong high pressure. As the weak front reaches Kauai late Tuesday
or early Wednesday, the robust surface high to the northwest will
drive increasing northeasterly trade winds and large rough seas.
The SCA has been expanded to all waters Tuesday due to
strengthening winds and building seas. This SCA may very well be
expanded for most waters, if not all, as the high settles north of
the area Friday and seas remain elevated. A decrease in trade
winds is expected heading into next weekend, but SCA conditions
could persist.

Latest near shore buoys show the 340-350 degree north-northwest
swell of around 5 ft at 12 seconds has shifted to a more
northerly (350-010 degrees) direction at around 4 ft 12 seconds
and will continue to slowly decline through today. Since this
swell is trending down, the threat of moderate surges in Kahului
and Hilo harbors no longer posses a threat thus the Marine Weather
Statement has been allowed to expire. Long- period forerunners
from the next northwest swell will arrive early Tuesday, and the
swell will peak at 9 to 10 ft Tuesday night and Wednesday. While
the resulting surf will easily exceed High Surf Advisory levels on
north and west facing shores, the peak of the swell will coincide
with fresh to near gale northeasterly winds, leading to rough
conditions and the potential for high surf along east facing
shores due to large wind waves. On Thursday, the swell will shift
out of the north- northwest and may be briefly reinforced, keeping
surf elevated around advisory levels. The northerly swell is
expected to decline late Friday into the weekend.

Small short-period wind waves and small wrapping northerly swell
will produce moderate east shore surf through today, followed by
a rise to around the advisory level Tuesday and Wednesday as
strengthening northeasterly trade winds produce large wind waves.
Above average east shore surf and rough conditions can be expected
Thursday and Friday due to fresh to near gale trade winds and
additional wrapping northerly swell. A small pulse of south-
southwest swell will fill in late Monday into Tuesday.


Small Craft Advisory from 6 AM Tuesday to 6 AM HST Wednesday 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.

Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.




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