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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 150201

Area Forecast Discussion
National Weather Service Honolulu HI
401 PM HST Fri Aug 14 2020

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.


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 are expected to 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

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.


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. Moderate to locally
breezy trades will then develop tonight into Saturday.

AIRMET Sierra will likely be required for windward areas tonight.
AIRMET Tango for lee turbulence may also be required as trades
increase overnight.


Moderate to fresh trades will 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. Therefore, a Small Craft Advisory has
been issued for the typical windier waters between Maui County
and the Big Island through Saturday 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
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 former TC 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.


Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.




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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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