531
FXHW60 PHFO 251335
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
335 AM HST Wed Sep 25 2024

.SYNOPSIS...
Gentle to breezy east trade winds will continue the next several
days. Rainfall will be limited with more cloudiness and brief
showers favoring windward exposures and higher terrain. The lone
exception will be along Kona region slopes of Big Island where
thicker cloud cover and showers will develop during daytime
hours.


&&

.DISCUSSION...
A large ridge of high pressure orientated parallel to the middle
latitudes is this week`s main Central Pacific synoptic scale
feature. The pressure gradient from the associated 1022 mb surface
high centered between 30N and 40N latitude and along 150W
longitude will continue to be the driver of gentle interior and
breezy coastal and mauka east trades into October. Low pressure
moving east across the Gulf of Alaska will ride atop this ridging
and nudge it slightly closer to the island chain. Overall, this
will have little to no effect on these ongoing gentle to breezy
east trades the next several days. The only subtle effect would be
a minor slackening of the gradient that could result in a hardly
noticeable weakening of late week easterlies to more gentle
magnitudes. The low will progressively move far northeast of the
region this weekend, allowing the ridge to rebound to the north.
This will likely correlate to the return of more statewide breezy
east trades early next week.

Mid to upper level ridging will build in over and north of the
islands during the remainder of the week. A vast majority of the
state`s 24 hour rainfall observations were zero this morning with
those that did pick up rain only measuring a few hundredths of an
inch (windward Big Island`s Mountain View was the winner with
slightly over a quarter of an inch since yesterday morning). Mid
layer moisture advection will not be overly abundant the next few
days with 850-700 mb relative humidity values consistently coming
in under 50%. This will translate to clearing out skies and
ultimately result in a dry weather pattern. Windward Big Island
and upper elevation Kauai will experience more periods of rain
through Friday. Pockets of greater than 90% mid layer RH passing
through the next few days will warrant high end chance to likely
rain probabilities in the Hilo and Puna Big Island districts and
generally above 2,000 ft on Kauai. The rest of the state will
experience brief shower activity that will generally favor the
windward slopes and highest terrain, especially overnight. More
frequent ribbons of high mid level moisture moving through from
the northeast and east early next week will increase areawide
rain chances and coverage.


&&

.AVIATION...
Moderate to locally breezy trade winds will continue due to high
pressure to the north of the area. Upper level high pressure
moving over the islands from the east will maintain a stable
airmass during this time. Some high clouds are streaming over
Kauai today from the south, but should shift to the west as the
mid-level features shifts west. Limited clouds and showers will
be carried in on the trade winds, focusing what few showers make
it to windward sides of the islands. Some afternoon clouds and
showers are possible over the Kona slopes of the Big Island. VFR
conditions are expected to prevail.

No AIRMETs are currently in effect and none are anticipated at this
time.


&&

.MARINE...
High pressure far north of the state will maintain moderate to
locally strong trade winds through this afternoon. Latest
observations and model guidance shows that winds will hover near
to just above Small Craft Advisory criteria through today with
conditions possibly dipping below advisory levels tonight. The SCA
remains in effect for the typical windy waters around Maui County
and the Big Island through today and will continue to be
monitored to see if an extension is warranted later this afternoon
or allowed to expire. Forecast remains on track with winds
further weakening this Friday and over the weekend as a front pass
north of the state, weakening and shifting the high far northeast
of the state. Moderate to locally strong trades may rebound as
early next week as the front dissipates and a new high quickly
rebuilds north of the state. Have removed chances of thunderstorms
from the offshore forecast as it appears the any thunderstorm
activity will stay just south and west of the area.

Latest offshore buoys 51001 and 51101 show a slow decline of the
moderate long period northwest swell (320 to 330 degrees) energy that
peaked locally overnight and early this morning. Should see a
gradually downtrend this afternoon through the rest of the work
week. A smaller north- northwest swell could provide a small,
short lived boost this weekend.

Surf along south facing shores will remain elevated through today
as a small, long period southwest swell peaks today with a gradual
decline tonight. In addition an overlapping short period
southwest swell is expected to fill in today from a fetch of
strong southwest winds that occurred Monday around 10N170W. A
smaller long- period southwest swell is possible Thursday night
into Friday before slowly declining over the weekend. Forerunners
of a small, long- period south- southwest swell is expected arrive
late over the weekend and peak early next week. East facing
shores should remain small through the rest of the week and into
the weekend due to the lack of strong trades locally or upstream
of the state.


&&

.FIRE WEATHER...
It is that time of year where Keetch-Byram Drought Index (KBDI)
values are greater than 600 in tandem with afternoon minimum
sub-50% relative humidity readings. As we are in a drier weather
pattern this week, fire weather conditions will worsen going into
late September. Short and mid term sustained winds at the Honolulu
Airport (PHNL) will likely remain below the 20 mph Red Flag
Warning criteria. Thus, critical fire weather conditions are not
expected for the rest of the week. However, many leeward areas
are in a moderate to severe drought and this alone elevates the
fire weather threat.

&&

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


&&

$$


DISCUSSION/FIRE...Blood
AVIATION...M Ballard
MARINE...Almanza