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Hawaiian Islands Synoptic Discussion and Guidance

393
FXHW60 PHFO 261327
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
327 AM HST Sun Jun 26 2022

.SYNOPSIS...
The hybrid trade wind and sea breeze pattern will continue on
today, as clouds build over leeward slopes of each island in the
afternoon hours, with some showers lingering from the afternoon to
the evening hours. An upper level disturbance will enhance cloud
and shower activity today and tonight. A high pressure system far
north of the Hawaiian Islands will build into the region on
Monday, increasing trade wind speeds to the moderate to locally
breezy range through Friday. Fairly typical cloud and shower
trends will return with passing showers over the windward and
mountain areas of each island, favoring the overnight to early
morning hours.

&&

.DISCUSSION...
Large scale satellite imagery this morning shows unstable cumulus
clouds drifting into region on the trade winds. An upper level low
shown on satellite water vapor imagery near Kauai with a trough
reaching eastward across the rest of the state will continue to
enhance shower activity today and tonight. Clouds and showers
today will favor both the windward areas and western slopes of
each island in a hybrid trade wind and sea breeze pattern. Local
radar imagery this morning continues to show scattered to numerous
showers developing across the region. Cirrus clouds from the
subtropical jet stream are drifting over the southeast islands
today. These ice crystal clouds will spread slowly northward to
all islands through the work week.

A hybrid trade wind and sea breeze weather pattern will continue
on today with sea breezes building clouds over leeward areas each
afternoon. An upper level low north of Kauai is producing a weak
troughing pattern aloft, lifting the trade wind inversion height
today into the 8,000 to 10,000 foot range based on the morning
upper air balloon soundings from Lihue and Hilo respectively.
Expect enhanced showers to continue for one more day as this low
and trough pattern drift westward away from the island chain.
Otherwise, a high pressure system far north of the state will
build into the region on Monday and strengthen the trade winds
from the current light to moderate levels into the moderate to
locally breezy range. These stronger trade winds will weaken the
sea breezes along terrain sheltered western slopes of the smaller
islands and bring a more typical trade wind weather pattern to the
region.

Model cross sections show variability in the trade wind inversion
height each day this week. Trade wind inversion heights will
range from around 6,000 to 8,000 feet from Monday onward, which
will keep passing showers in the forecast mainly over windward and
mountain areas. These windward shower amounts will be light and
favor the overnight to early morning hours. Leeward slopes of the
smaller islands however will remain on the dry side with only
isolated showers possible. The western slopes of the Big Island
may continue to see isolated to scattered showers each afternoon
to early evening in a persistent sea breeze regime.

&&

.AVIATION...
Light to moderate trades will persist into tonight, with
localized land and sea breezes expected in some of the more
sheltered leeward areas. Although VFR conditions will prevail for
most areas, expect brief periods of MVFR CIGS/VSBYS in and around
showers that develop and move through. The exception is over the
eastern end of the state, where MVFR conditions are being observed
over a larger area early this morning. As a result, AIRMET Sierra
remains in effect for mountain obscuration across windward/SE
sections of the Big Island and windward Maui. These conditions may
continue through the morning hours before improving.

&&

.MARINE...
Trade winds will hold at gentle to moderate speeds through
tonight as a front passes between the islands and a surface high
well north of Kauai. High pressure will build far northeast of
the state Sunday night, leading to an increase in trade winds
Monday. A Small Craft Advisory will likely be issued tonight for
the typically windy waters around the Big Island and Maui through
at least the middle of the week, and likely through next weekend.

Two pulses of south swell will produce elevated south shore surf
this week. The first swell is now showing up at the nearshore
buoys, with Barbers Point coming in at 2 feet 18 seconds at the
latest observation. Surf will build along local south shores today
as this swell fills in. Surf is expected to peak a couple of feet
overhead Monday, then build to near advisory level of 10 feet
Tuesday and Wednesday as the next, larger, pulse arrives. South
swell and surf will gradually decline Thursday and Friday.

Surf along exposed north and east facing shores will see a bump
in small, short period swell today into Monday. Surf along north
shores will drop Tuesday, while strengthening trade winds will
boost rough east shore surf to around seasonal average.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

None.

&&

$$

DISCUSSION...Bohlin
AVIATION...Gibbs
MARINE...TS

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

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RH		8 %
Wind		N 11 mph
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