Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 240657
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
857 PM HST Fri Feb 23 2024

.SYNOPSIS...
High pressure to our north will keep trade winds blowing across
local waters through the forecast period. Wind speeds will
strengthen over the weekend as the pressure gradient steepens,
remaining breezy through much of the new week. Clouds and showers
will favor windward and mauka areas.

&&

.DISCUSSION...
Troughing to the west of the main Hawaiian Islands, combined with
a high to our north, keeps winds blowing from the east to east
southeast across local waters this evening. Satellite loop shows
thick middle and high clouds just north of the islands, marking
the northern flank of the subtropical jetstream. Patchy broken low
clouds are noted across windward and mauka sections of the
smaller islands. Radar shows scattered to numerous moderate
showers associated with this low cloud cover. Afternoon soundings
show a stable airmass, with positive lifted index values.

Overall, expect a trade wind distribution of clouds and showers
through the forecast period, with minor variations defendant on
airmass stability and pressure gradient steepness. Models show
that winds should turn to a more easterly direction statewide, and
possibly strengthen, by tomorrow as the troughing to our west
retreats westward and the high to our north becomes the main flow
driver. Showers embedded in this flow will focus rainfall across
windward areas. The almost zonal subtropical jetstream across the
islands may enhance these showers at times. Expect a somewhat
drier airmass to fill in after the current batch of moisture
passes westward tonight. Showers will continue to favor windward
areas, but total rainfall will be light. Breezy trade winds will
push some showers to leeward areas.

By late next week, models show an upper trough will move over the
islands from the northwest, introducing a pool of destabilizing
cold air aloft. At the surface, high pressure will remain north of
the state and trade winds will persist at the surface. However,
associated trade showers may be heavier and more widespread as the
upper trough moves in.

&&

.AVIATION...
Breezy easterly trade winds will remain in place through the next
few days and will focus showers primarily over windward and
mountain areas. An increase in shower coverage and intensity is
expected tonight through tomorrow morning as bands of clouds and
showers associated with an old front move through from east to
west with the trade wind flow. MVFR conditions can be expected
within the passing showers.

AIRMET Sierra is in effect for the island of Kauai due to mountain
obscuration from the showers and will likely continue through the
evening. This AIRMET will also likely be expanded to include
other islands later this evening as bands of showers move through.
AIRMET Tango may also be needed for moderate low-level turbulence
tonight or tomorrow as surface wind speeds increase a bit.

&&

.MARINE...
Trade winds will shift out of the east and become fresh to strong
for most waters this weekend through early next week. The Small
Craft Advisory has been expanded to most Hawaiian waters, which
will continue through the weekend. The waters around Kauai and
Oahu will likely be added later tonight for those winds coming up
on Saturday.

An upward trend in surf along north and west facing shores is
expected over the weekend as a fresh, long-period north-northwest
swell arrives late tonight, then builds down the island chain.
This swell will peak late Saturday through Saturday night. We are
keeping the surf forecast just below advisory levels for the moment,
since confidence is not high enough for a High Surf Advisory.However,
will monitor the buoys as the swell arrives in case one is needed.
A slow downward trend is expected by late Sunday.

Surf along exposed north and east facing shores will trend up early
next week as a medium-period north-northeast swell arrives. Surf
heights will likely reach the advisory levels (potentially near the
warning level for east facing shores)as this swell peaks Monday
through Tuesday. Otherwise, short-period/rough surf is anticipated
along exposed eastern shores due to the strong trades locally and
upstream.

Surf along south facing shores will potentially trend up late next
week due to the arrival of a long-period south swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Saturday for Oahu Windward
Waters-Kaiwi Channel-Maui County Windward Waters-Maui County
Leeward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-
Big Island Windward Waters-Big Island Leeward Waters-Big Island
Southeast Waters.

&&

$$

DISCUSSION...Powell
AVIATION...Vaughan
MARINE...Foster


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