758
FXHW60 PHFO 220106
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
306 PM 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 and
scattered showers across windward Big Island and Maui through
this evening. 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 light to moderate
winds through early next week.

&&

.DISCUSSION...

High pressure centered about 250 miles north of Honolulu as of
the 18Z surface analysis will continue to weaken and sag south
this evening. As it does so, it will maintain light to moderate
northeast trade winds through this afternoon that will weaken
overnight to become light and variable by morning. While most of
the state will continue to remain dry with only a few light
isolated showers moving into windward areas this afternoon,
increased low level moisture continues to stream into windward Big
Island and Maui, bringing scattered showers to those areas. 00Z
upper air soundings showed persistent stable conditions at Lihue
with a precipitable water value of 0.89" and a strong temperature
inversion around 5000 feet. At Hilo, inversion heights continue to
be higher at around 9000 feet and precipitable water was measured
at 1.32", which once again makes sense based on the increased
shower activity around this area.

As land breezes develop across most of the island chain tonight,
shower activity will remain minimal for the smaller islands and
begin to diminish across Maui and the Big Island. While low
clouds are expected to clear out overnight, high clouds will begin
to build in from the northwest as a jet streak moves overhead
tonight into tomorrow.

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
the deterministic global models differ in how they handle a weak
front that is expected to approach from the northwest. However,
they seem to have come into slightly better agreement this
afternoon. According to the latest model guidance, it looks like
the weak front will approach Kauai`s doorstep Sunday night, then
dissipate as it gradually moves towards Oahu and Maui on Monday
and Tuesday. Impacts look to be minimal with light to moderate
northerly winds moving in with the front, along with the potential
for a slight uptick in shower activity for the western end of the
state, but the bulk of the moisture associated with the front
should remain to the east of the island chain. Unrelated to the
front, low level tropical moisture moving in to windward Big
Island will bring a little increase in shower activity for that
end of the state from late this weekend through early next week.
High pressure will then settle in across the state behind the
dissipated front on Wednesday and bring a return to light to
moderate easterly trades heading into the latter part of the
week.

&&

.AVIATION...

Winds have trended downwards as expected, and are expected to
continue this trend through Friday. A high pressure system and
its associated ridge remain north of Kauai this afternoon, and it
is drifting southward towards the islands. With the weakening
trade winds, expect some localized land and sea breezes.

Showery low clouds continue to hug the north through east sides of
Maui and the Big Island this afternoon, 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. Although conditions have started to improve over
Maui, enough clouds remain that the AIRMET is expected to remain
in place into tonight. Confidence is higher that the clouds will
linger over the Big Island through tonight. Elsewhere, expect VFR
conditions to prevail. No other AIRMETS are in effect or are
expected tonight.

&&

.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 medium period small to moderate
pulses out of the NNE (010-030) associated with the strong storm
off the US Pacific Northwest coast. 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
or NE 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