560
FXHW60 PHFO 210639
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
839 PM HST Fri Sep 20 2024

.SYNOPSIS...
Breezy easterly trades will continue through Saturday, then
briefly ease into the light to moderate range Sunday through
Monday as the surface ridge weakens to the north. Showers will
primarily favor windward and mauka locations, though a few could
reach leeward and interior areas as an upper disturbance drifts
southward over the region Sunday. Breezy trades and more stable
conditions are expected to return Tuesday, persisting into the
latter half of next week.

&&

.DISCUSSION...
Guidance remains in good agreement, showing breezy easterly
trades holding through Saturday as the surface ridge stays far
north of the state. Evening satellite imagery shows a couple of
sizable areas of low clouds approaching from the east, which may
lead to enhanced windward and mauka shower coverage overnight into
Saturday as they move through.

A slight transition is expected Saturday night through Monday as
upper heights lower in response to a broad, weak upper low
drifting southward into the area, while the surface ridge weakens.
Lighter trades, combined with a weakened subsidence inversion,
could lead to increased windward showers, with some either
spilling over into leeward and interior areas or forming over
leeward areas due to localized sea breezes in the afternoon. The
best chance for thunderstorms will remain north of the state where
the better mid-level lapse rates and deeper moisture are
expected.

Upper heights will rise Monday night through midweek as the upper
low fills and lifts away. This, combined with the surface ridge
rebuilding to the north, will support a return to a more stable
and breezy trade wind pattern. Although confidence is low this far
out, some models suggest an area deeper tropical moisture
associated with a disturbance passing far south of the state
clipping portions of the area late next week. Expect a wetter
trade wind pattern for these areas if this were to materialize.

&&

.AVIATION...
Moderate to locally breezy trades are expected through the rest of
tonight. An upper level low is anticipated to move over the state
during the weekend time frame. Enhanced SHRA are expected mostly
over windward and mauka locations, with limited spillover to
leeward areas. MVFR conds can be expected with isolated IFR conds
in heavier prolonged SHRA. VFR should generally prevail outside of
SHRA activity.

No AIRMETs are in effect. With an increase in SHRA overnight
AIRMET Sierra may be needed for mtn obsc for windward locations
during the overnight hours through this weekend.

&&

.MARINE...
A high pressure ridge far north of Hawaii will keep fresh to
strong easterly trade winds in the forecast through Saturday. A
cold frontal system passing through the far northern Central
Pacific basin will weaken the ridge from Sunday through Monday,
briefly easing trade wind speeds into the gentle to moderate
range. A Small Craft Advisory (SCA) remains in effect for the
windier waters around Maui County and the Big Island through
Saturday. Fresh trade winds should return by Tuesday of next week
and the trades may approach SCA thresholds for our typical windier
waters around Maui County and the Big Island once again.

Surf along north and west facing shores will trend up beginning
next Tuesday in response to a gale developing near the Kurils,
racing eastward across the Date Line near the Aleutians this
weekend, then to the Gulf of Alaska early next week. Guidance
shows this northwest swell peaking locally Tuesday night into
Wednesday out of the northwest, then fading Thursday into Friday
as it shifts out of a more north-northwest direction.

Surf along south facing shores will remain small through the
weekend, with mainly a mix of background long-period southwest and
short-period southeast swells moving through. An upward trend is
possible Tuesday through midweek due to a slightly larger
southwest swell arriving.

Surf along east facing shores will remain small and choppy into
Saturday, then decrease Sunday into next week as the trades lower
locally and upstream across the eastern Pacific.

&&

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

&&
$$

DISCUSSION...Gibbs
AVIATION...Walsh
MARINE...Bohlin