030
FXHW60 PHFO 211904
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
904 AM HST Thu Nov 21 2024

.SYNOPSIS...

Gradually diminishing trade winds will deliver just a few light
showers to windward areas of most of the smaller islands today,
with a greater concentration of showers across windward Big
Island and Maui. Light and variable winds and mostly dry weather
are expected statewide from tonight into Sunday. A weak front may
move over the islands from the northwest late this weekend into
early next week. However, little impact is expected from this
front as it`s expected to bring minimal rainfall and winds should
remain light through early next week.

&&

.DISCUSSION...

No changes to the forecast from earlier this morning as the
forecast philosophy remains the same.

High pressure centered about 300 miles north of Honolulu as of the
12Z surface analysis earlier this morning will continue to weaken
and sag south today. As it does so, it will maintain light to
moderate winds that will weaken tonight to become light and
variable and likely allow for land breeze development statewide.
While most of the state will remain dry with only a few light
isolated showers moving into windward areas today, low level
moisture continues to stream into windward Big Island and Maui,
bringing scattered to numerous showers to those areas. 12Z upper
air soundings showed stable conditions at Lihue with a
precipitable water value just below an inch and a strong
temperature inversion around 5000 feet. At Hilo, inversion heights
were higher at around 9000 feet and precipitable water was
measured at 1.42 inches, which makes sense based on the increased
shower activity around this area. As land breezes develop tonight,
this shower activity should begin to diminish.

Background winds will remain light through the weekend as the
surface high moves overhead and dissipates, with land and sea
breeze activity expected. With little available moisture, shower
activity will remain limited through the weekend, with only light
isolated to possibly scattered showers expected with the
afternoon sea breezes.

Forecast details become a bit uncertain heading into next week as
a weak front is expected to approach from the northwest.
Deterministic global model guidance differ on how they handle the
progression this front, but ensemble guidance is showing a higher
confidence in relatively dry conditions with light winds through
early next week.

&&

.AVIATION...
A high pressure system and its associated ridge remain north of
Kauai this morning, leading to a decrease in trade winds across
the islands. This will likely result in some localized land and
sea breezes as the trades gradually weaken through Friday.

Showery low clouds are moving into the windward sides of Maui and
the Big Island this morning, bringing some periods of MVFR
conditions to those areas. Some of the heavier showers may
produce brief IFR conditions. AIRMET SIERRA is in effect for
these areas, and is expected to remain in place through today.
Elsewhere, expect VFR conditions to prevail. No other AIRMETS are
in effect or are expected today.

&&

.MARINE...

Weak high pressure positioned immediately north of the islands
maintains gentle to locally moderate E trades into Saturday. A
weak cold front advancing into the area further diminishes the
gradient this weekend causing trades to turn variable to light
NEly through the first half of next week.

Swell out of the NW quadrant remains small through Friday. Medium
period, moderate NW (310-320) swell then builds during Saturday
and is forecast to peak shy of High Surf Advisory (HSA) criteria
on Sunday before subsiding early next week. Overlapping with this
NW swell will be a series of moderate period small to moderate
pulses out of the NNE (010-030) associated with the strong storm
off the US Pacific Northwest. This swell is likewise forecast to
peak shy of HSA criteria for N facing shores, though marginal HSA
potential will be worth monitoring for susceptible E facing
exposures Saturday through Sunday. Short period fresh trade wind
swell and wind waves subside in concert with weakening trades.

&&

.FIRE WEATHER...

KBDI values remain high across the state and an overall dry
weather pattern is expected for the next several days. With this
dry air moving overhead, relative humidity values will have the
potential to reach the critical 45% threshold from late morning
through the afternoon each day through Sunday. Fortunately,
however, weak trade winds will mitigate fire weather concerns
through the rest of this week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Farris
AVIATION...M Ballard
MARINE...JVC