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Hawaiian Islands Synoptic Discussion and Guidance

279
FXHW60 PHFO 141958
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
958 AM HST Fri Aug 14 2020

.SYNOPSIS...
High pressure far to the north of the area will provide for a
trade wind weather pattern across the state. Clouds and passing
light showers will favor windward and mauka areas with just a few
showers possible over select leeward locations. An upper low will
move over the area toward the middle of next week possibly
increasing shower coverage across the state.

&&

.DISCUSSION...
A 1029 mb surface high is centered far to the north of the state.
This places the islands in a moderate trade wind regime. Moisture
embedded in the trades is producing a few light passing showers
over windward and mauka areas while leeward locations are
generally dry.

Trade winds may pick up a bit tonight through Saturday night as
a weak area of low pressure passes by south of the state,
tightening up the pressure gradient just a bit. Aloft, a ridge of
high pressure will be building in from the east keeping the
airmass on the stable side. Shower activity will continue to favor
windward and mauka areas and will be highly dependent on incoming
moisture availability.

By Sunday, trade winds will be on the decline as a front begins
to drop southward far to our north. This will disrupt the pressure
gradient causing trade winds to become lighter. More wind sheltered
areas will likely experience daytime sea breezes under this weather
regime. A few passing showers can be expected mainly over windward
and mauka areas.

By the middle of next week, an upper low is forecast to drop down
over the area from the north. This will cause some destabilization
of the airmass over the area. This may allow for greater shower
coverage but shower activity will still be dependent on incoming
moisture availability.

&&

.AVIATION...
Moderate trades will become moderate-to-breezy tonight into
Saturday. A weak trough approaching the Islands from the east
will bring an increasing coverage of showers and MVFR to windward
areas beginning with the Big Island this evening and spreading
across the remainder of the islands through tonight.

No AIRMETs are in effect. AIRMET Sierra for tempo mountain
obscuration may be needed for windward areas tonight.

&&

.MARINE...
Moderate to fresh trades will continue today, then briefly increase
into the fresh to strong category tonight through late Saturday
as the pressure gradient tightens over the islands in response to
low pressure passing far to the south. This will likely translate
to a Small Craft Advisory being issued for the typical windier
waters between Maui County and the Big Island later this afternoon.
Guidance shows winds weakening Sunday into early next week as the
area of low pressure to the south continues westward and the
ridge weakens.

Surf along east facing shores will hold steady into the weekend
near or just under the advisory level of 8 ft as a moderate
northeast swell moves through. North facing shores exposed to this
swell will also see a small increase in surf. Surf will gradually
ease Sunday into early next week as the winds relax locally and
the swell drops. Although confidence remains low, a small easterly
swell is still possible this weekend due to distant tropical
cyclone Elida in the eastern Pacific, especially for the eastern
end of the state.

Surf along south facing shores will remain small through Saturday,
then gradually trend up Sunday into early next week as a small,
south-southwest swell arrives. WAVEWATCH III guidance shows a
reinforcement from the same direction Monday night through
Tuesday, which should hold through midweek before easing.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...BB
AVIATION...JVC
MARINE...TS

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



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