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Hawaiian Islands Synoptic Discussion and Guidance

355
FXHW60 PHFO 261339
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
339 AM HST Mon Feb 26 2024

.SYNOPSIS...
High pressure to the north of Hawaii will maintain breezy trade
winds through the week. Clouds and showers will favor windward and
mauka areas, with the gusty winds carrying some showers over
leeward areas at times.

&&

.DISCUSSION...
The forecast was modified with the morning package to align the
PoPs and associated grids towards the NBM. Overall the changes are
minor. Through midweek, the PoPs were increased a bit over some
windward areas. During the end of the week, the forecast was made
a little wetter.

A robust strong surface high remains far north of Oahu continues
to drive breezy trades over the area. Mid-level ridging over the
islands is helping to maintain a stable airmass overnight.
Overnight soundings showed little change, with an inversion based
between 6000 to 8000 ft, and precipitable water running slightly
below the seasonal normal. As a result, breezy trades will
continue, and will carry passing moderate showers over windward
slopes. Expect some spotty showers over the Kona slopes of the
Big Island this afternoon. The gusty trades could still carry
some of the showers to leeward areas on the smaller islands.

Expect little change through much of the week. The surface high
will weaken slightly Monday and Tuesday, but the pressure gradient
over Hawaii will hold firm as the high sinks a little southward.
As a result we are expecting the breezy and gusty trade winds to
change little. Another high will move north of Hawaii by
Wednesday, and maintain breezy trades through at least Friday.
Random patches of moisture in the trade wind flow will bring
periodic boosts in mainly windward rainfall over the next several
days, with the next area passing through late tonight and Monday
morning. Chances for more widespread rainfall and a few heavier
showers will increase on Thursday and Friday as an upper-level
trough digs to the west of the islands and moves to the east over
the islands.


&&

.AVIATION...

Breezy trade winds will remain in place through at least midweek.
Clouds and light showers will favor windward coasts and slopes,
and be most active in the late night and morning hours. AIRMET
Sierra for mountain obscuration will likely become necessary for
northeast slopes of Kauai and the Big Island later this morning
with conditions expected to last trough mid-afternoon. VFR
conditions are expected to prevail elsewhere.

In the afternoon and early evening, lee-side sea breezes and
daytime heating will encourage cumulus build-ups along south and
west facing slopes of the Big Island, but a strong inversion aloft
around 07 kft will limit their growth.

AIRMET Tango remains in effect for moderate low-level turbulence,
and will likely be needed through midweek. Additionally, the
proximity of a passing upper level jet streak may trigger isolated
moderate upper-level turbulence this morning.


&&

.MARINE...
An area of large high pressure centered approximately 1,300
nautical miles north of the islands is producing a tight enough
pressure gradient back toward the state to maintain fresh to
locally strong trade winds. Little overall change in the near term
Central Pacific weather pattern will occur in the coming days as
the high remains anchored north of the area and maintains these
stronger winds the next several days. A Small Craft Advisory
(SCA) remains in effect for all Hawaiian nearshore waters
primarily due to these winds but also for relatively higher seas
produced by a passing northeast swell. Little change in the
overall nature of these strengthened trades and agitated seas has
the all-water SCA now in effect through (at least) Tuesday night.
Winds may trend down a touch going into the middle of next week
as the high gets replaced by another slightly weaker high to the
northwest and moves closer to the islands.

The only show in town swell-wise will be a new moderate size, short
to medium period northeast (40-60 degree) swell originating from a
close proximity gale low. As evidenced by the swell being observed
at Buoy 51000 around midnight, it will be filling into the nearshore
waters later this morning, peaking during the afternoon and evening
hours. A High Surf Advisory (HSA) is in effect for all east-facing
shores through early Tuesday morning. The HSA may need to be extended
in time on Tuesday. Days of fresh to locally strong trades has
produced a rough, short period wind wave and, with no substantial
break in the trades, rough conditions are expected to continue
along eastern shores. East-facing shore surf trends will have to
be closely monitored through the day. The northeast swell mixed in
with elevated trade wind waves does create a low probability that
rough east surf could briefly reach 15 foot warning thresholds.
Weekend eastern passing southern hemispheric gale lows have
produced swell energy that will eventually make it into our
local waters Thursday. Thus, south-facing shore surf may increase
by another foot or two later this week with the arrival of these
small, longer period south swells.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Tuesday for Olomana-Maui
Windward West-Kauai East-Kauai South-Koolau Windward-Molokai
Windward-Molokai Southeast-Windward Haleakala-Kipahulu-Big
Island East-Big Island North.

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


&&

$$


DISCUSSION...M Ballard
AVIATION...Bedal
MARINE...Blood

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