172
FXHW60 PHFO 312000
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1000 AM HST Fri May 31 2024

.SYNOPSIS...
Surface high pressure positioned far northeast of the state
will maintain a tight enough pressure gradient across the region
to support breezy to locally windy trade winds into early next
week. Showers moving in on the trades will favor windward areas
and likely become more prevalent during the nocturnal hours. An
upper trough developing over the islands the next few days will be
the impetus to increased shower frequency and areal coverage.


&&

.DISCUSSION...
The synoptic set up across the Central Pacific has changed very
little these past few days. This being of a near 1030 mb high
centered approximately 1,100 miles from Oahu with a pesky surface
trough about 900 miles west of Kauai. These two features have
created a tight enough pressure gradient between them to hold
primarily breezy regional trade winds in place. Dry 12Z local
soundings are evidence of a very dry air mass where precipitable
water values are registering in the lower 10% percentile range for
late May. Enhanced stability is also noted in both satellite,
radar and soundings as the 5-6k foot subsidence inversion sustains
a shallow somewhat dry boundary layer. The surface high will only
subtly settle southward as the trough washes out through the day.
This will slightly tighten the gradient over and upstream of the
islands enough to provide a minor uptick in weekend trade wind
magnitudes. The only other near term mentionable change will occur
with increasing mid level moisture this weekend that will likely
lead to more frequent windward showers that will expand across a
larger area.

Heights will lower over the state into the weekend. Extended NWP
guidance is still a little out of phase with the location of the
lowest heights or mid-upper level troughing over the islands. The
emergence of the subtropical jet over or just south of the state
this weekend may offer more argument to a wetter commencement of
June, but this is very dependent upon its positioning. While there
will be some eastern moisture advection, the mid levels of the
atmosphere will remain fairly dry until Tuesday and this may
weigh forecast philosophy toward more dry. Regardless of any minor
model nuances, there continues to be moderate confidence that
next week`s upper troughing scenario will increase areal shower
coverage and intensity...especially going into the middle of next
week due to increased lower and mid layer moisture. Trades may
become disrupted late next week in response to the passage of a
surface trough/front to the north.


&&

.AVIATION...
Breezy to locally strong easterly trade winds are expected to
increase slightly this weekend, as a surface high moves closer
to the state from the northeast. Clouds and showers will continue
to favor windward slopes with periodic MVFR conditions possible,
especially during the overnight to early morning hours when an
uptick in shower activity is expected. Otherwise and elsewhere,
VFR conditions will prevail.

Winds of 20 to 30 kts are expected to persist below an inversion
between 5000 and 7000 feet. These conditions justify continuance
of AIRMET Tango for tempo moderate low-level turbulence south
through west of terrain. In addition, strong jet stream winds
passing over Hawaii today through Friday warrant AIRMET Tango for
tempo moderate turbulence aloft between FL300-FL400.

AIRMET Sierra for mountain obscuration is cancelled for all areas,
as shower activity has decreased and ceilings have improved.


&&

.MARINE...
A 1030 mb surface high centered 1100 nm NE of the islands will
change little as it sags slowly S over the next couple of days,
resulting in a slight increase in ENE trade wind speeds. Fresh to
strong trade winds will prevail into early next week, and an
existing Small Craft Advisory (SCA) for the windier zones around
Maui and the Big Island is slated to expand to most zones tonight.
Long-range guidance indicates a trend toward diminishing and
veering winds around the middle of next week as the ridge to the N
is weakened by a passing front.

There will be an extended run of elevated surf along S facing
shores over the next week (and likely longer), with the largest
of the swells likely to produce surf near High Surf Advisory
(HSA) levels of 10 feet. The first of several pulses of long-
period SSW swell will gradually build today, and peak near HSA
heights over the weekend. Latest buoy observations indicate modest
energy increases in the longer periods, resulting in inconsistent
and small sets. Additional pulses of swell arriving early next
week will persist through the middle of the week, with the
potential for a larger swell by the following weekend.

A strong, slow-moving low in the distant NW Pacific has generated
a small NW swell that will arrive Monday and Tuesday, with the
potential for a small follow-up NW swell generated by the extra-
tropical version of former west Pacific Typhoon Ewiniar. Trade
winds will continue to generate short-period wind waves that will
support choppy surf along exposed E facing shores.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory from 6 PM this evening to 6 PM HST Saturday
for Kauai Northwest Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters.

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$


DISCUSSION...Blood
AVIATION...TS
MARINE...Birchard