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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 142019
Area Forecast Discussion
National Weather Service Honolulu HI
1019 AM HST Fri Dec 14 2018
Breezy trade winds will persist through tonight due to surface
high pressure north of the islands. The winds will gradually
diminish from this weekend into early next week as this high moves
slowly south and weakens. A stable weather pattern with brief
windward and mauka showers will prevail through Monday. Expect dry
conditions across most leeward areas. A front is expected to move
down the island chain from late Tuesday through Wednesday,
bringing an increase in showers and breezy northeasterly trade
A surface high is centered several hundred miles north of the
state. This places the islands in a moderate to locally breezy
trade wind environment. The airmass in the island vicinity is
rather dry and stable as indicated by the 12Z soundings from both
Lihue and Hilo. Satellite imagery shows stable low clouds moving
westward in the trades but radar imagery shows very little in the
way of precipitation falling from them. These conditions will
continue through the day today. A Wind Advisory has been posted
through tonight for the Big Island summits with sustained wind
speeds exceeding 45 MPH being reported. Winds are expected to
diminish later tonight and Saturday.
The global models are in good agreement for the upcoming weather
scenario. A cold front will be passing by far north of the state
this weekend. It will nudge the surface high a bit to the south
resulting in a deceleration of the trades from present levels. The
airmass is expected to remain rather dry and stable so only a few
light showers are expected over windward and mauka areas with most
leeward locations remaining dry through the weekend.
By Monday, another cold front will be approaching the area from
the northwest. This front will push the surface high off to the
northeast of the area with trade winds dropping off to lighter
levels. Local land and sea breezes may develop in some areas under
this lighter wind regime.
By the time the front reaches the island vicinity, it is expected
to be rather shallow and weak with the best upper level dynamics
remaining far north of the state. Current timing shows the front
reaching Kauai late Tuesday, then spread down the island chain
Tuesday night through Wednesday night. Breezy north to northeast
winds will accompany the frontal passage. This will cause the
greatest increase in shower activity over north and northeast
facing slopes and well as areas immediately downwind of terrain.
With the front being rather shallow, heavy rainfall is not
expected. A drier trade wind weather pattern is expected to follow
in the fronts wake.
High pressure centered N of the islands will move S weaken over
the next 24 hours, allowing strong and gusty trade winds to
gradually ease. The interaction between the ENE trade winds, the
island terrain, and a subsidence inversion based around 6000 feet
will continue to produce low-level turbulence to the S and W of
all islands. In fact, latest satellite imagery shows low- level
wave clouds extending up to 100 miles to the SW of the islands.
AIRMET Tango for low-level turbulence will remain posted into at
The trade winds will deliver scattered, primarily stable, low clouds
that will focus over windward slopes and coasts. Brief periods of
MVFR VIS/CIG in -SHRA, are expected, but the strongly-capped and
relatively dry atmosphere will keep rainfall very light. VFR conditions
will prevail at all TAF sites through tonight.
Strong trade winds will continue today with high pressure passing
north of the area. A combination of winds and seas will maintain
Small Craft Advisory (SCA) conditions today across all coastal
waters. The current northwest swell is on the decline and expected
to remain below High Surf Advisory (HSA) levels through Saturday.
As the swell subsides, seas will drop below SCA levels. Trade
winds are expected to weaken some tonight and Saturday. By
tonight, some of the coastal waters will drop out of the SCA, and
additional areas will drop below criteria tomorrow.
A large northwest swell will build late Saturday, peaking Sunday
at warning levels, and start to subside Monday. An even larger
northwest swell will build late Monday, once again peaking at
warning levels. These swells will once again bring seas in excess
of 10 feet to the waters exposed to these swells. At the same
time, moderate to locally breezy trade winds will continue to
bring SCA level winds to the typically windier areas near Maui
County and the Big Island. The result will be SCA conditions for
most, if not all, the coastal waters for the first half of the
The HSA in effect today for east facing shores of Kauai, Oahu,
Molokai, Maui, and the Big Island is due to short-period, rough
surf produced by the strong trades. Surf should lower below
advisory levels by this evening as the trades ease.
See the latest Oahu Surf Discussion (SRDHFO) for additional
details on surf and swell.
High Surf Advisory until 6 PM HST this evening for Kauai
Windward-Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-
Windward Haleakala-South Big Island-Big Island North and East.
Wind Advisory until 6 AM HST Saturday for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for all
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office