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Hawaiian Islands Synoptic Discussion and Guidance

344
FXHW60 PHFO 180627
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
827 PM HST Mon Dec 17 2018

.SYNOPSIS...
Dry and pleasant conditions will hold into Tuesday. Trade winds will
continue to trend down, potentially enough for land and sea breezes
late tonight through Tuesday for portions of the state as a weak
cold front approaches and moves into the area. The front is forecast
to quickly advance down the island chain late Tuesday through
Wednesday, bringing increasing rain chances. Gusty northerly winds
along with drier and cooler conditions will follow Tuesday night
through Thursday. A return of a more typical trade wind pattern will
be possible Friday into the upcoming weekend.

&&

.DISCUSSION...
Short-term (through Thursday) guidance remains in good agreement
and reflects the dry and pleasant pattern continuing into Tuesday.
Precipitable water values are forecast to hold below average for
this time of year through a good portion of the day tomorrow,
ranging from three quarters of an inch to around an inch. After a
long stretch of breezy to windy trades, the pressure gradient has
relaxed over the state in response to a weak cold front and upper
trough approaching from the northwest. Trades have responded and
trended down into the light to moderate range this evening based
on recent observations. Expect this downward trend to continue
overnight, potentially becoming weak enough for localized land/sea
breezes through Tuesday for much of the state.

The cold front is forecast to advance down the island chain
beginning later in the day Tuesday for Kauai, then stall around the
Big Island Wednesday night into Thursday. A slight increase in
moisture (albeit shallow) combined with this boundary and upper
trough will support a band of clouds and increasing rain chances
late Tuesday through Wednesday as the boundary moves down the island
chain, mostly over the northern and windward sides of the islands.
Rain chances will likely remain up over the Big Island through
Thursday as the boundary hangs up and gradually diminishes.

Gusty northerly winds along with much drier and cooler conditions
will follow the frontal passage Tuesday night through Thursday. Wind
advisory criteria being exceeded for the typically windier areas
exposed to northerly winds can't be ruled out, mainly Tuesday night
through Wednesday. Dewpoints are forecast to dip into the upper 50s
for portions of the state. High temperatures may struggle to reach
the 80 deg mark Wednesday afternoon.

For the extended (Friday through the weekend), guidance supports a
return of a more typical trade wind pattern by the weekend with
clouds/showers focusing over windward areas.

&&

.AVIATION...
A surface front approaches the islands from the northwest will
result in the weakening of trade winds across the area through
early Tuesday. A slight increase in low clouds in the island
vicinity is expected, though mainly VFR conditions will prevail
for all sites.

As the front advances near Kauai later on Tuesday, winds will
turn more northerly and increase for the smaller islands. A
further increase in cloud coverage with some showers are expected
for the smaller islands, especially along the windward areas.

No AIRMETs are in effect or expected through early Tuesday. AIRMET
Tango for TURB may be needed later on Tuesday as brisk northerly
winds spread across the area. Even AIRMET MTN OBSC is a
possibility along the windward mountains.

&&

.MARINE...
Light to moderate trades will hold in place through early Tuesday
as a cold front approaches the state from the northwest. The cold
front will sweep through Kauai Tuesday afternoon, through Oahu
and Maui County Tuesday night, then hang up in the vicinity of the
Big Island on Wednesday. Strong northerly winds will fill in along
and behind the front, bringing solid Small Craft Advisory (SCA)
level winds to all marine zones, and potentially a brief period
of Gales to the Alenuihaha channel. High pressure will build
eastward well to the north of the islands Wednesday through early
next week, with strong winds returning to a more typical east-
northeasterly trade winds direction late Wednesday and Wednesday
night. Moderate to locally strong trades will then continue
Thursday through early next week.

Long-period forerunners from a new northwest swell have hit the
NOAA buoys 51001 and 51101 this evening and will continue to move
southeastward toward the island chain through the night. Surf is
expected to begin building over exposed north and west facing
shores late tonight, reaching advisory levels around daybreak
Tuesday. Surf will continue to rise through the day Tuesday and
likely reach warning levels by late in the afternoon. Surf is
expected to peak Tuesday night through Wednesday, then gradually
lower through the rest of the week. The peak of the surf is
expected to occur near the peak of the spring high tides during
the pre-dawn hours on Wednesday, giving way to above average
coastal wave run-up.

A High Surf Warning remains in effect for exposed north and west
facing shores from midnight tonight through Tuesday night. A High
Surf Advisory remains in effect for north facing shores of the Big
Island from 6 AM Tuesday through Tuesday night. These headlines
may eventually need to be extended through Wednesday. A SCA
remains in effect for all Hawaiian waters for winds, seas or a
combination of the two through Wednesday. The SCA will likely need
to be extended for much of the marine area through Thursday.

Surf is expected to drop below the winter time average along
north and west facing shores for the latter part of the week, and
on into the weekend. A small to moderate northwest swell will be
possible early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning from midnight tonight to 6 AM HST Wednesday
for Niihau-Kauai Windward-Kauai Leeward-Waianae Coast-Oahu North
Shore-Oahu Koolau-Molokai-Maui Windward West-Maui Central Valley-
Windward Haleakala.

High Surf Advisory from 6 AM Tuesday to 6 AM HST Wednesday for
Big Island North and East.

Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian
waters-

&&

$$

DISCUSSION...Gibbs
AVIATION...Hui
MARINE...Jelsema

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

Current Conditions
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RH		11 %
Wind		ESE 6 mph
Road		Open (4x4)