473
FXHW60 PHFO 201937
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
937 AM HST Fri Sep 20 2024

.SYNOPSIS...

A moderate to locally breezy trade wind pattern will continue
through this evening. Shower activity is expected to increase
this weekend as a weak disturbance moves through the Hawaii
region. A drier and more stable trade wind pattern will return
early next week.

&&

.DISCUSSION...

Satellite and radar imagery show low clouds and scattered showers
moving into windward areas on the trades this morning, with a few
showers circumnavigating or passing over some of the island
terrain into leeward areas at times. High clouds can also be seen
moving across the region from the west. Temperature inversion
heights around 9000 feet as measured at Hilo around 2 AM this
morning are allowing for brief moderate downpours. A moderate to
breezy trade wind pattern will continue today, with shower
activity expected to decline later this morning into the
afternoon. While seasonal temperatures are expected again today,
if the high clouds thicken up persist through the day
temperatures might be slightly lower than average this afternoon,
but model simulated satellite imagery shows that these high clouds
should gradually decrease in coverage through the day.

A shift in the pattern is expected this weekend as the trades
weaken on Saturday in response to a weak low level trough
approaching from the northeast, an upper level low dips down over
the state from the north Saturday night into Sunday, and another
weak low level trough moves in from the west. With modest
forcing in both the low to mid levels and pockets of low level
moisture in the trades, trade wind showers will likely be enhanced
this weekend, especially Saturday night into Sunday. In addition,
cooler temperatures aloft will move overhead with the mid to
upper level low, allowing instability to increase...which raises
the question of whether or not we`ll see any thunderstorms this
weekend. With only marginal instability, small pockets of low
level moisture, and weak surface forcing, decided to hold to the
previous forecast philosophy and keep any mention of thunder out
of the gridded forecast through the weekend.

A drier and more stable moderate trade wind pattern will return
early next week as the upper level low and surface trough both
move west of the state. Brief overnight to early morning showers
will be possible over mainly windward and mountain areas.

&&

.AVIATION...
Moderate to locally breezy trade winds will carry pockets of
moisture, leading to periods of MVFR conditions along windward
slopes through the next 24 hours. AIRMET Sierra for mountain
obscuration has been dropped for windward Big Island, Maui, and
Molokai, but these conditions may redevelop over some islands
overnight. VFR will prevail over leeward areas. An upper-level
low will move over the state during the weekend and could bring a
more active shower pattern with higher chances for MVFR conditions
over windward and mauka areas by Saturday night.

&&

.MARINE...
Fresh to strong easterly trade winds will continue through
Saturday, then ease into the gentle to moderate range Sunday
through Monday as a weakness forms in the ridge to the north. A
Small Craft Advisory (SCA) remains in effect for the windier
waters around Maui County and the Big Island through early
Saturday. This may need to be extended through the day Saturday,
before being lowered as the winds begin to trend down during the
latter half of the weekend.

Surf along north facing shores will trend up through the first
week of fall, beginning next Tuesday in response to a gale
developing near the Kurils today, 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 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.

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.

&&

.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...Farris
AVIATION...Wroe
MARINE...Kino