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Hawaiian Islands Synoptic Discussion and Guidance

357
FXHW60 PHFO 231352
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
352 AM HST Fri Aug 23 2019

.SYNOPSIS...
Moderate to breezy trades will continue through the weekend, then
trend down into the light to moderate range early next week.
Clouds and showers will favor windward and mountain locations,
especially through the overnight and early morning periods as
pockets of higher moisture move through. The exception will be
over the leeward areas of the Big Island, where afternoon and
evening clouds and showers form in response to the local sea
breeze.

&&

.DISCUSSION...
The latest surface analysis showed a weakness within the
subtropical ridge due to an upper low and surface trough north of
the islands. Despite this weakness, breezy trades are holding over
the state. Clouds and showers are focusing over the typical
windward locations. Rainfall accumulations, however, have remained
light over the past six hours (through 2 AM HST), with
accumulations ranging from a tenth to around a quarter of an inch.

Moderate to breezy trades will continue over the weekend as the
upper low and surface trough continue westward and high pressure
builds to the north. An increase in shower coverage will be
possible late Saturday into Sunday as a pocket of higher moisture
moves through from east to west. Although most of the shower
coverage will focus over windward and mountain locations, some
will manage to spill over into leeward locations with the gusty
trades expected. Model PWs within this pocket of higher moisture
are forecast to climb into the 1.75 to 1.9 inch range over the Big
Island late Saturday, then to the smaller islands Saturday night
into Sunday.

For the extended period, guidance remains in decent agreement
through the first half of next week and shows a weakness
developing within the ridge to the north as a broad upper trough
and surface front pass to the north. The pressure gradient is
forecast to respond and weaken over the state, which will allow
the trades to lower into the light to moderate range (localized
land and sea breeze conditions possible).

&&

.AVIATION...
A high pressure ridge north of the state will keep moderate trade
to locally breezy trade winds in the forecast through the weekend.
Mostly VFR conditions are expected over all islands with isolated
MVFR conditions in scattered showers along east slopes of all
islands.

AIRMET Tango remains in effect today for moderate turbulence
south through west of mountain ranges. This AIRMET will likely
continue through the afternoon.

&&

.MARINE...
High pressure to the north will maintain moderate to locally
strong trades through the weekend. Thus, the Small Craft Advisory
(SCA) has been extended through Sunday for the typically windy
waters around Maui and the Big Island. The Small Craft Advisory
may need to be expanded into other zones late in the weekend as
the high strengthens north of the state.

The current south swell will be on its way out through the day
today with mainly background energy expected over the weekend
into early next week. A larger southwest swell is expected to
arrive Tuesday and will likely peak Wednesday or Thursday of next
week. Surf is expected to peak near borderline advisory levels.

Small northwest swells will linger over the next few days
providing some out of season surf along north facing shores.
Fresh 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 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Gibbs
AVIATION...Bohlin
MARINE...Kino

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



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