Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 190631
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Wed Jan 18 2017

.SYNOPSIS...
High pressure east-northeast of the state will keep mainly moderate
to fresh trade winds through Thursday. Winds will become locally
light and variable Thursday night and Friday as a front approaches
from the northwest. The 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.

&&

.DISCUSSION...
Trade wind weather continues across the islands this evening as a
high pressure remains far east-northeast of the area. There are some
low clouds in the island vicinity. These clouds are not bringing
much, if any, precipitation as air mass stays rather dry and stable
as depicted by earlier afternoon soundings. Latest satellite imagery
does show some more low clouds just upstream east of the islands,
but then as weather conditions remain unfavorable for rainfall
development, hence expect mainly fair weather to prevail across the
state through rest of the evening into early Thursday morning.

The high far east-northeast will move further east on Thursday,
while a cold front far northwest of area will advance closer to the
islands. This will result in the gradual weakening of trade winds
later on Thursday. Nevertheless, still expect mainly trade wind
weather on Thursday, with passing low clouds and showers affecting
mainly windward and mountain areas. Rainfall amounts will remain low
as airmass will still be stable.

Lighter synoptic winds by Thursday night 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 over the daytime and
some clearing at time. Once again, precipitation will be limited due
to stable weather pattern.

Northeast winds will dramatically increase late Friday night into
Saturday as the cold front sags near the state with a strong high
builds far north behind the front. The strong pressure gradient will
develop across the area, resulting in very windy trade winds for the
islands through the weekend. Winds will likely be strong enough to
reach advisory levels for all or 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.

The front is still expected to stall near the Big Island early next
week with winds veering east. Winds will turn more southeast and
becoming light across the state as another front is forecast to
approach the islands from the northwest. Both long range GFS and old
ECMWF still keep much of the moisture associated with this front
just north to northeast of the state as it passes the area late
Monday into Tuesday.

&&

.AVIATION...
High pressure northeast of the state will keep a light to moderate
trade wind flow in place, with clouds and very light showers
affecting mainly windward and mauka areas. Brief MVFR cigs will
be possible in windward areas, but predominantly VFR conditions
are expected through Thursday.

AIRMET Tango remains in effect for low level turbulence over and
downwind of the terrain. These conditions are expected to remain
in place through the night.

&&

.MARINE...
The new west-northwest swell is expected to peak late tonight and
early Thursday, then lower gradually later Thursday and Thursday
night. With the more westerly direction of this swell, high surf
will also reach west-facing shores of The Big Island later tonight
and Thursday. Another large northwest swell is expected to arrive
Thursday night 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. (However, winds are
expected to drop off later tonight and Thursday.) 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.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM HST Thursday 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 Thursday for west facing shores
of Oahu.

Small Craft Advisory until 6 PM HST Thursday for all Hawaiian
waters except Maalaea Bay

&&

$$

AVIATION...Jelsema
MARINE...Kinel
REST...Hui



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