High Surf Advisory 57, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Mon Dec 3 2018

.SYNOPSIS...
Trade winds will prevail through the week, becoming breezy and
gusty on Tuesday and again by the weekend. Showers will be focused
along windward slopes through much of the week under the trades.
Moisture from a dissipating front will keep windward Big Island
somewhat wet, while leeward areas remain rather dry. The trailing
end of another weak front will bring an increase in rainfall as it
moves down the island chain over the weekend.

&&

.DISCUSSION...
Moderate trade winds continue across the state this evening, as a
1024-25 mb surface high is about 600 miles north of the state. A
ridge aloft is moving over the area from the northwest and will keep
airmass stable in the island vicinity. Hence, trade wind weather
prevails across the islands, with passing low clouds and showers
affecting mainly windward areas. Windward Big Island may see a
little clouds and showers though, as moisture from a dissipating
front, carried by the trades, reaches the area at times.

Winds will pick up on Tuesday, and little change is expected in
regards to the rainfall pattern. The pressure gradient across the
region tightens slight, leading to a slight strengthening of the
winds. The lingering frontal moisture will continue to affect mainly
windward Big Island, but may reach windward east Maui at times. In
addition, the building trade winds may reach wind advisory strength
over the summits of the Big Island on Tuesday.

Winds will briefly ease on Wednesday as an approaching front from
the northwest weakens the surface high and displaces it eastward.
The atmosphere will remain stable, and the forecast solutions showed
no organized areas of low level moisture nearby. As such, expect
similar trade wind weather to persist, with windward rainfall and
mostly dry leeward conditions. Models do hint a slight increase in
moisture on Thursday, so a slight increase in windward showers is
possible.

Building high pressure northwest of the islands will lead to trade
winds increasing again late Friday over the weekend. In fact, winds
may get rather breezy by the later part of the weekend. Forecast
solutions also indicated the tail end of a front will reach the
island chain over the weekend. Even there are differences on the
models upon how fast and how far south this weak front will
ultimately advance to, moisture from the front will be affecting
the islands. The anticipated strong trade winds will easily push
some clouds and showers over lee areas of the smaller islands. The
gusty trade winds may even reach wind advisory strength across some
areas during the weekend.

&&

.AVIATION...
High pressure north of the state will drive breezy trades over the
Hawaii next few days. AIRMET Tango remains in effect for areas south
and west of all mountain ranges below 8000 ft MSL due to tempo
moderate turbulence.

Remnant moisture and clouds from an old frontal boundary east of the
Big Island will recycle clouds and showers westward, enhancing cloud
heights and shower activity for all islands through the morning
hours. Expect scattered to numerous showers with MVFR ceilings and
visibility favoring windward and mountain areas. AIRMET Sierra was
expanded to include north and east sections of all islands this
evening.

Both AIRMET Sierra and Tango will last at least through Tuesday
morning.

&&

.MARINE...
High pressure north of the state will keep a moderate to breezy
trade wind flow in place across the coastal waters through the work
week. There will likely be a slight easing of the trades late
Wednesday through Thursday as a cold front passes by north of the
island chain. The trades will then increase late in the work week
and become quite strong over the weekend through early next week as
a front slips down the island chain and strong high pressure builds
northwest of the state. A Small Craft Advisory remains in effect for
the typically windy waters around Maui and the Big Island through
Wednesday. A large incoming northwest swell will build from
northwest to southeast Tuesday afternoon and Tuesday night, and as a
result the SCA will need to be expanded to include the remainder of
the marine area. SCA conditions will then likely continue for most
and possibly all marine zones through early next week. The trades
may even be strong enough over the weekend to produce Gales across
the typically windy waters around Maui and the Big Island.

The current small northwest swell will slowly fade through Tuesday.
A new large northwest swell associated with an intense low over the
northwest Pacific several days ago, will build Tuesday afternoon,
peak Tuesday night and Wednesday, then slowly lower through the
remainder of the week. Warning level surf is expected along exposed
north and west facing shores during the peak of the event, with
advisory level surf possibly continuing through Friday night.

Short-period, rough surf will gradually increase along east facing
shores during the first half of this week as trade winds increase to
moderate and locally breezy levels. East shore surf will lower
slightly Wednesday night through Friday as trade winds upstream of
the state decrease. East shore surf will then increase Friday night
through early next week as the trades strengthen upstream of the
islands once again, with advisory level surf possible by early next
week. Surf along south facing shores will remain small through the
forecast period.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

DISCUSSION...Hui
AVIATION...Bohlin
MARINE...Jelsema