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WindENE 29 mph
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 191348

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Thu Jan 19 2017

High pressure far east-northeast of the state will keep light to
moderate trade winds today. Winds will become locally light and
variable tonight and Friday as a front approaches from the
northwest. This front will advance across the smaller islands over
the weekend, then stall near the Big Island early next week, with
increasing showers across the state. Additionally, very strong trade
winds are expected for the state this weekend, before easing early
next week.


Trade wind weather continues across the islands early this morning
as a high pressure remains far east-northeast of the area. Low
clouds have filled in a bit along the windward coastal waters
overnight and are bringing some showers mainly to windward and
mountain areas. Early morning Lihue and Hilo soundings continue to
depict a rather dry and stable airmass in the island vicinity.
Therefore, rainfall amounts from these passing showers will be
limited. The aforementioned high will move further east today, while
a cold front far northwest of area will advance closer to the
islands. This will result in the gradual weakening of trade winds
throughout the day. Nevertheless, still expect mainly trade wind
weather today, with passing low clouds and showers affecting mainly
windward and mountain areas.

Lighter synoptic winds by tonight and Friday will allow more
widespread localized nighttime land breezes and daytime sea breezes
to develop over the islands. Furthermore, weather may become a
little more convective, with clouds developing during the day, then
some clearing at night. Once again, precipitation will be limited
due to the stable weather regime.

Northeast winds will dramatically increase late Friday night into
Saturday as a cold front advances near the state, while a strong
high builds far north behind the front. The strong pressure gradient
expected to develop across the area will result in very windy trade
winds for the islands through the weekend. Winds will likely be
strong enough to reach advisory levels for at least portions of the
state. Along with the winds, an increase in showers is expected.
Showers will be most prevalent across windward and mauka areas, but
with the increasing trades and rising inversion heights, some of the
showers will reach leeward areas of the smaller islands as well.
Strong winds will also keep showers moving rather swiftly across the
area, limiting the rainfall accumulations somewhat.

The front is still expected to stall near the Big Island early next
week with winds veering east. Winds will turn more southeast then
becoming light across the state as another front is forecast to
approach the islands from the northwest. Both long range GFS and
ECMWF still keep bulk of the moisture associated with this next
front just north to northeast of the state as the main frontal
boundary passes northeast of the area Tuesday. The islands are
expected to see moderate northerly winds briefly after this front
exits east.


High pressure northeast of the state will keep a light to moderate
trade wind flow in place today, with winds diminishing tonight as a
front approaches from the northwest. Predominantly VFR conditions
are expected through tonight, with brief MVFR cigs in light showers
or mist possible across mainly windward and mauka areas.

AIRMET Tango remains in effect for low level turbulence over and
downwind of the terrain of all islands. Boundary layer winds are
expected to diminish later this morning and the AIRMET will be
cancelled when this occurs.


The west-northwest swell is expected to peak early today, then lower
gradually later today and tonight. With the more westerly direction
of this swell, high surf will also reach west- facing shores of The
Big Island today. Another large northwest swell is expected to
arrive tonight and Friday with advisory level surf expected. This
swell will lower gradually over the weekend. A short period
north-northeast swell is expected over the weekend behind a cold
front moving across the area. The swell will gradually swing around
to the east early next week. Advisory level surf is likely along
north and east facing shores with this new swell. Another large
northwest swell is expected for next Tuesday and Wednesday.

A Small Craft Advisory is presently posted for most Hawaiian coastal
waters, mainly due to seas associated with the new west- northwest
swell. Winds around portions of The Big Island are also reaching
Small Craft Advisory levels, though they are expected to drop off
today. Winds behind a cold front moving across the chain this
weekend will exceed advisory criteria and could reach Gale Warning
levels across some areas. Also, seas will remain rather high through
the weekend and into early next week.


High Surf Warning until 6 PM HST this evening for north and west
facing shores of Niihau, Kauai, for north facing shores of Oahu,
Molokai and Maui, and for west facing shores of the Big Island.

High Surf Advisory until 6 PM HST this evening for west facing
shores of Oahu.

Small Craft Advisory until 6 PM HST this evening for all Hawaiian
waters except Maalaea Bay.




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