940
FXHW60 PHFO 021351
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
351 AM HST Sun Jun 2 2024

.SYNOPSIS...
Breezy trades will continue into the middle of the week, before
weakening and giving way to land and sea breezes during the second
half of the week. An upper level trough over the islands through
Tuesday may bring some heavier showers at times, especially over
interior Big Island where there will be also be a chance for
afternoon thunderstorms.


&&

.DISCUSSION...
No major changes to the forecast this morning, however the winds
for the Big Island summits over the next couple days was nudged
upwards. Used a blend of the ECMWF and the GFS to account for the
upper level trough moving over the islands which will bring some
stronger, but still below advisory level, winds into mid week.

The overall forecast philosophy remains the same. A breezy trade
wind pattern to remain in place through Tuesday. A mid to upper
level trough has moved closer to the islands from the east
overnight. The overnight soundings from Lihue and Hilo haven`t
shown many changes, but expect colder temperatures at the 500 mb
to move in tonight.

High pressure remains far to the northeast of the islands, with a
ridge north of 30N, which will maintain the breezy trade wind
pattern into the middle of the week. Satellite derived
precipitable water shows a drier airmass has moved over the
smaller islands, and that is reflected in the Lihue sounding
overnight which reported 1.12 inches. More moisture is found near
the Big Island where the sounding had 1.28 inches. Several gages
on the eastern side of the Big Island have reported more than an
inch of rain since last evening. Anticipate additional showers
over the east side of the Big Island, and to a lesser extent over
Maui. The remaining islands will have some clouds overhead, but
the chance for showers will be significantly lower.

A mid to upper level trough moving over the islands from the east
will lead to an increasing unstable airmass over the islands
through Tuesday. The trough is expected to sharpen and pivot over
the islands during this time, before lifting north and then east
away from the region. The global models are in good agreement that
this trough will bring colder temperatures to 500 mb. The ECMWF
keeps temperatures around -10/-11C, while the GFS brings in even
colder temperatures of -12/-13C. These temperatures are
significantly colder than normal for June. At 700 mb there isn`t
much different in the temperatures between these models with
temperature getting to around 4/6C which is colder than normal but
not as climatologically colder. Additional the coldest
temperatures at 700 mb look to be focused near Kauai, while the
colder 500 mb temperatures reach most of the islands.
Thunderstorms were added with the afternoon package to the Big
Island forecast for Monday and Tuesday afternoon, with the best
chance being Tuesday afternoon. Leeward island plumes over the
nearshore waters will also be candidates for nocturnal
thunderstorm activity during this time, however confidence is
lower so that is not currently reflected in the forecast.

The second half of the week will see the a new mid-level ridge
setting up far northwest of the islands, as a front north of the
islands weakens to a trough. This will cause our winds to weaken
and turn to the southeast. This could lead to some land and sea
breezes over the islands. With a decrease in precipitable water
and a more stable airmass overhead, expect a decrease in shower
activity, with clouds and showers more likely during the afternoon
and evening hours over interior and southeast facing portions of
the islands.


&&

.AVIATION...

Breezy to strong trades will continue, as a surface high moves
closer to the state from the northeast. Low cigs and SHRA will
favor windward and mauka areas with periods of MVFR conds possible
in any SHRA. VFR conds should prevail elsewhere.

AIRMET Sierra is in effect for mtn obsc for windward Big Island
and N thru SE sections of the smaller islands.

AIRMET Tango remains in effect for moderate low- level turb S thru
W of terrain, as well as for moderate turb between FL300-FL400.

AMD NOT SKED for PMDY as equipment remains unavailable with no
time table for return to service.


&&

.MARINE...

A 1028 mb surface high centered about 900 nm NE of the islands
will remain nearly stationary through the remainder today. A
Small Craft Advisory (SCA) has been scaled back to only include
zones in the typically windy areas around Maui county and the Big
Island. The high is expected to weaken slightly on Monday, but
will still help to support fresh to locally strong ENE trade winds
through Tuesday. On Wednesday, a frontal system approaching from
the northwest will allow the high to weaken significantly, and
lead to light and variable winds through the end of the week.

An extended period of elevated surf along S facing shores is now
underway, with numerous swell pulses expected, mainly from the
SSW. A High Surf Advisory (HSA) is likely to be needed for the
largest of the swells, which may not arrive until next weekend.
Nearshore buoys S of the islands continue to indicate increased
energy in the longer 15-17 second period bands this morning,
equating to elevated surf, but below HSA levels. This swell
likely peak today into Monday, then gradually ease Tuesday before
additional long-period swells arrive.

A strong, slow-moving low in the distant NW Pacific generated what
will be a small NW swell when it arrives in the islands Monday
and Tuesday (3 to 4 foot medium period swell from 320 direction),
with the potential for a small follow- up NW swell later in the
week. Trade winds will continue to generate short- period wind
waves that will support choppy surf along exposed E facing shores
the next couple of days.


&&

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


&&

$$


DISCUSSION...M Ballard
AVIATION...Walsh
MARINE...Thomas