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Hawaiian Islands Synoptic Discussion and Guidance

441
FXHW60 PHFO 091325
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
325 AM HST Thu Jul 9 2020

.SYNOPSIS...
The breezy trade wind pattern will continue through early next
week. Windward shower coverage is expected to increase today
through early Friday as a mid-level disturbance and higher
moisture move through from east to west. Drier trade wind
conditions will prevail Friday through early next week.

&&

.DISCUSSION...
Latest surface analysis and satellite imagery showed the
subtropical ridge anchored north of the islands and patchy low-
level clouds approaching and moving through from east to west.
Some of these clouds are generating brief/moderate showers as
they move through - mainly over windward and mountain areas. Rain
gages around the islands reflect this and showed peak
accumulations up to an inch over the past 6-Hrs (through 2 am HST)
on Kauai. Satellite-estimated precipitable water (PW) imagery
depicted a decent sized area of higher moisture approaching from
the east within a hundred miles of the Big Island (values up to
around 1.6 to 1.7 inches).

Guidance has initialized well with this upstream moisture and
shows it moving into the eastern end of the island chain this
morning, then to the western end of the state later today through
early Friday. A combination of this moisture, a mid-level trough
moving through and breezy trades will support an increase in
windward shower coverage through this time. Some will be briefly
heavy and make it into leeward areas. Drier air will follow
beginning Friday as this moisture and mid-level feature shift west
of the area.

Although confidence remains very low being this far out in time,
model solutions are trending toward a wet middle- to latter-half
of next week as a remnant trough associated with Tropical Storm
Cristina in the far eastern Pacific approaches and moves into the
area. Additional fine tuning of the forecast will be expected
over the coming days as forecast confidence rises and guidance
converges on a solution.

&&

.AVIATION...
Strong high pressure far northeast of the state will continue to
generate moderate trade wind flow. Surface wind speeds will
gradually decrease over the next twenty-four hours. Breezy winds
at summit level combined with a well defined inversion aloft at
approximately 09kft are generating low level mechanical turbulence
to the lee of higher terrain. AIRMET Tango remains in effect, but
will likely be canceled toward evening as summit level winds
decrease.

Bands of low topped cumulus showers embedded in the trade wind
flow will continue to impact mainly north and east facing slopes
and coasts. AIRMET Sierra for mountain obscuration is in effect
for Windward Kauai and conditions are expected to persist through
at least mid-morning. Elsewhere, VFR conditions predominate.

Meanwhile across Leeward Big Island, weak land breezes in the
late night and morning hours will give way to light sea breezes in
the afternoon and early evening. Sea breeze driven cumulus build-
ups are expected to redevelop across Leeward and Interior Big
Island this afternoon and linger through the evening hours.

&&

.MARINE...
Fresh to strong trade winds will prevail through the weekend and
into early next week, as strong high pressure holds in place far
north and northeast of the islands. A Small Craft Advisory (SCA)
remains in effect for the typically windier waters around Maui
and the Big Island through Sunday. This SCA will likely need to be
extended into early next week.

No significant swells are due through much of the week. A mix of
mainly background southerly swells will dominate, with a south-
southwest swell giving south shore surf a bit of a boost today
through Friday. Trade wind swell will gradually build to around
the summer average today, then hold into early next week. A small
long-period swell from tropical cyclone Cristina could arrive
early next week as well. Surf along north facing shores will
remain small through the next 7 days.

&&

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

&&

$$

DISCUSSION...Gibbs
AVIATION...Bedal
MARINE...Jelsema

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

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RH		38 %
Wind		ENE 11 mph
Road		Open (4x4)