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RH14 %
WindENE 0 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

615
FXHW60 PHFO 280641
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
841 PM HST Tue Sep 27 2022

.SYNOPSIS...
Moderate trade winds will remain on the dry side of normal for most
areas through Thursday, but moisture associated with a dissipating
front may bring an increase in windward showers to Kauai beginning
Wednesday. An increase in windward showers is possible statewide
Thursday night and Friday as moisture arrives from the east. Light
and variable winds this weekend may bring increased afternoon
showers to island interiors, with generally dry conditions at night.

&&

.DISCUSSION...
A mostly dry and stable weather pattern is in place over the islands
this evening, with latest satellite images showing few low clouds
moving toward the islands within a moderate E trade wind flow. Wispy
high clouds to the SW of the islands are moving SSE within the flow
aloft, with a stabilizing mid- and upper level ridge centered NW of
the islands. Afternoon soundings show a strong subsidence inversion
based near 7000' over the Big Island, while the Lihue sounding
showed a weaker inversion, with PWAT near 1.3". Little change is
expected in the short term, with just a few windward showers
possible overnight.

Model guidance over the past 36-48 hours has been leading the
forecast to anticipate an increase in PWAT near Kauai as remnants of
a front, now about 200 miles N of Kauai, sags S. This has yet to
occur, but some guidance continues to indicate that this moisture
will bring an increase in low-level moisture, and NE trade winds, to
Kauai and vicinity, potentially as early as Wednesday morning. This
is expected to lead to increased coverage of trade wind showers over
windward Kauai, while mostly dry conditions persist over the
remainder of the state during the mid-week period. Worth noting that
latest high resolution model guidance doesn't bring the NE wind
shift or much increase in showers to Kauai until Wednesday night.
The forecast may need some adjustment to fine tune the timing, with
latest guidance also indicating much less potential for heavy
showers, with moisture depth remaining 8000' or less.

A brief uptick in trade wind shower coverage is possible Thursday
night and Friday moisture associated with a low-level trough
presently near 20N 145W moves over the area. Global model consensus
depicts a slow-moving cut-off low developing far NE of the islands
toward the end of the week, with the associated front moving very
close to the islands over the weekend, substantially weakening the
local pressure gradient. The emerging land/sea breeze pattern will
have the lingering increased moisture with which to work,
potentially favoring a healthy coverage of afternoon clouds and
showers over interior sections through the weekend, with land
breezes bringing clearing each night. Increased moisture associated
with the dissipating front may move over the islands early next
week.

&&

.AVIATION...
High pressure north of the state will produce moderate trade winds
through the forecast period. A relatively dry airmass will keep
cloud and shower activity minimal through tonight, with the possible
exception of windward Big Island. Any showers that do develop will
focus over windward slopes. VFR conditions will prevail, with brief
MVFR conditions possible in passing showers.

No AIRMETs are in effect.

&&

.MARINE...
A weakening frontal boundary remains north of the Hawaiian Islands
this evening with a high pressure system far to the northeast of the
state Trade winds will remain in the moderate to fresh range through
Thursday. Wind speeds will then weaken from Friday through Sunday,
as yet another low pressure system sets up north of the region. Wind
speeds will likely remain below Small Craft Advisory thresholds
through Sunday.

South swell will continue to lower through Wednesday. Another small
background south swell will fill in Thursday with a slight
reinforcement expected Friday and Saturday. A slightly larger long
period south swell may arrive around Sunday.

A series of small medium period west-northwest swells are expected
throughout the week. Long range models are hinting at a cut off low
forming far north of the state sending a north swell to the islands
by this weekend. Forecast guidance continues to show different
locations on this developing cut off low, thus our confidence on
this weekends north-northwest swell height remains low at this time.
East facing shores will remain small over the next week, with a
potential of the north swell wrap early next week.

&&

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

&&

$$

DISCUSSION...Birchard
AVIATION...Ahue
MARINE...Bohlin

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office