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RH14 %
WindNNE 11 mph
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Hawaiian Islands Synoptic Discussion and Guidance

634
FXHW60 PHFO 221939
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
939 AM HST Thu Aug 22 2019

.SYNOPSIS...
Expect a typical trade wind weather pattern through the weekend,
with clouds and showers favoring windward and mauka areas. Warm
and humid conditions are forecast Tuesday through midweek as
wind speeds trend down into the light and variable range.

&&

.DISCUSSION...
An upper low and a dissipating surface trough north through
northeast of the islands puts a dent in the subtropical ridge.
That said, locally breezy trade winds continue across local waters
this morning. Satellite loop shows clouds focusing across windward
and mauka areas of the islands, with denser cloud cover noted over
and upwind from Kauai and Oahu. Radar shows isolated to scattered
showers within these clouds.

Models show trade winds decreasing briefly Friday through early
Saturday as the upper low and dissipating surface trough pass
westward. Kauai may see increased windward shower coverage tonight
into Friday as the moisture axis associated with the trough moves
through. Elsewhere, mostly dry conditions will prevail with
clouds and showers favoring windward and mauka areas. Moderate to
breezy trades will return over the weekend as high pressure builds
to the north. An increase in shower coverage is possible late
Saturday into Sunday as a pocket of higher moisture moves through
from east to west.

After the weekend. models show a weakness developing within the
ridge as a broad upper trough and surface front pass to the north.
The pressure gradient will weaken over the state, possibly allowing
a land and sea breeze regime to develop Tuesday through midweek.
If this scenario evolves, clouds and showers will favor interior
areas through the afternoon and evening hours.

&&

.AVIATION...
A ridge N of the area will maintain locally strong E flow over
the main Hawaiian Islands.

A band of showery low clouds will be moving W across Kauai for
the next few hours. AIRMET Sierra is in effect for MTN OBSC on
Kauai due to low ceilings and visibilities. VFR conditions will
prevail elsewhere but ISOL MVFR ceilings or visibilities are
possible over E sections of the islands.

&&

.MARINE...
High pressure to the north will maintain mostly fresh trades
through Friday. The typical windy areas around Maui and the Big
Island will continue to see locally strong trades. Thus, the
Small Craft Advisory (SCA) has been extended through tonight for
the typically windy waters around Maui and the Big Island. A
trough approaching from the north will briefly ease the trade
winds Friday night to below SCA levels. A new high building
northeast of the islands will then strengthen winds back to
moderate and locally strong levels over the weekend, with SCAs
likely being required once again for the windier marine zones.

The High Surf Advisory for south facing shores has been dropped
and the south swell will continue to lower through the rest of the
week. A series of small long-period south and southwest swells
will move through Sunday through early next week. A larger southwest
swell is possible Tuesday through the second half of next week.

Small northwest swells will linger over the next few days
providing some out of season surf along north facing shores.
Breezy trades will continue to produce small choppy surf along
east facing shores over the next few days. An increase in wind
swell is expected late in the weekend as trades strengthen locally
and upstream of the state.

&&

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

&&

$$

DISCUSSION...Powell
AVIATION...Donaldson
MARINE...Morrison

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