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Hawaiian Islands Synoptic Discussion and Guidance

729
FXHW60 PHFO 181940
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
940 AM HST Thu Aug 18 2022

.SYNOPSIS...
Trade winds will gradually strengthen today. Daytime sea breezes
will continue to be more extensive than normal, and a disturbance
disturbance could trigger a few, briefly heavy showers over
leeward areas this afternoon along with a thunderstorm over
interior Big island. A drier and more stable moderate trade wind
flow will prevail Friday through the weekend, focusing rainfall
over windward areas and across the Kona slopes of the Big Island.
Trade winds may ease early next week as another disturbance
potentially brings an increase in shower activity.

&&

.DISCUSSION...
Instability will linger today as trade winds gradually build from
east to west. The resurgent trades will be driven by a
strengthening surface ridge now located nearly 400 miles north of
Kauai. This will bring showers to windward areas, mainly across
Maui County and the Big Island. Daytime sea breezes will
overpower the building trade winds over many leeward areas,
leading to afternoon interior and leeward clouds with spotty
showers. A weak disturbance sitting over the state will provide
enough instability to cause a few of these showers to be heavy,
and interior Big Island could experience an afternoon
thunderstorm.

Trade winds will build to moderate strength tonight and Friday,
and a ridge aloft building in from the east will bring increased
stability. The surface ridge driving the trades will hold about
400 miles north of Kauai through the weekend and produce moderate
trade winds. No significant sources of moisture are noted in the
trade wind flow, pointing toward modest rainfall over windward
areas and a few showers over leeward Big Island slopes each
afternoon. Other leeward areas will be mainly dry.

Trade winds will ease early next week as the ridge to the north is
weakened. An increase in showers will be possible as a mid and
upper level trough and some associated deeper moisture moves in
from the east.

&&

.AVIATION...
A weak trade wind pattern will ensue today and help generate
isolated to scattered showers along mainly the windward coasts
and slopes. Weak instability east of Maui will lead to slight
chance of thunderstorms this afternoon over the Big Island...
initiated by diurnal heating.

By tonight, expect trade winds to strengthen and bring scattered
showers to the windward coasts and slopes. This activity may
cause brief periods of MVFR ceilings and visibility.

&&

.MARINE...
A surface ridge just north of the state is keeping trade winds on
the lighter side this morning. The ridge is forecast to drift
northward over the next few days resulting in trade winds
increasing. A Small Craft Advisory will be posted for the
typically windier waters around Maui County and the Big Island by
noon HST today. Trade winds may become a bit lighter around
Monday as a frontal system far northwest of the area nudges the
ridge axis closer to the state.

The current small south swell will linger through tonight. A new
long period south swell will begin to fill in late Friday and
Friday night. This swell is expected to be rather long lived
peaking around Sunday with surf heights possibly reaching low end
advisory levels. This swell will slowly diminish early next week.
Short period choppy surf will increase into the weekend with the
expected uptick in trade wind speeds over and upwind of the state.
North facing shores will remain just above summertime flat levels
through the weekend. A frontal system far northwest of the state
may send a small northwest pulse early next week.

&&

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

&&

$$

DISCUSSION...Wroe
AVIATION...Thomas
MARINE...Burke

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



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