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Hawaiian Islands Synoptic Discussion and Guidance

674
FXHW60 PHFO 191313
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
313 AM HST Wed Dec 19 2018

.SYNOPSIS...
A weak front that has moved down the island chain overnight is
forecast to stall and diminish over and around the Big Island today
through tonight. Showers associated with the front will favor
northern and windward sections of the islands early today, then
potentially linger over the eastern end of the state into Thursday
as the boundary stalls. Gusty northerly winds along with drier
and cooler air will fill in across the western end of the state
through Thursday. A return of a more typical trade wind pattern is
expected Friday into the upcoming weekend. Increasing rainfall
chances will become a possibility early next week as another front
approaches.

&&

.DISCUSSION...
Gusty northerly winds along with drier and cooler air behind a cold
front will continue to fill in across the state from west to east
today. The front will reach the Big Island early this morning,
then stall and diminish by Thursday. A shallow band of moisture
associated with this boundary combined with northerly winds and
the island terrain will continue to support numerous showers for
the northern and windward sections of Maui County and the Big
Island. The latest rainfall summary showed peak totals exceeding
2.5" at West Wailuaiki on windward Maui and up to 3.5" on Molokai
over the past six hours as of the 2 am HST. Similar shower
coverage will continue over Maui County and the Big Island
today as the boundary begins to stall. Elsewhere, a drying trend
is expected today.

In addition to the shower coverage, gusty northerly winds with
speeds exceeding advisory levels over portions of Maui County and
the Big Island can be expected. This has resulted in a wind
advisory for portions of Maui County (Lanai and Maui Central
Valley) and the Big Island (Kohala and southeast Kau/Puna slopes)
through tonight.

Temperatures may struggle to reach the 80 degree mark through the
afternoon hours today due to the drier and cooler air filling in.
Dewpoints are forecast to dip into the upper 50s.

A transition period is expected Thursday as the low-level flow
shifts around to a more typical trade wind pattern. Residual
moisture along the stalled boundary will support the best rainfall
chances over the Big Island through the day Thursday. Otherwise,
guidance supports trade wind conditions prevailing Friday into
the weekend with clouds/showers focusing over windward areas.

Rainfall chances may climb once again early next week due to a
better source of moisture moving into the area and another cold
front approaching from the northwest. More specifics will come in
later packages as confidence rises.

&&

.AVIATION...
A weak front has been moving through the islands and bringing
breezy to strong north to northeast winds and intermittent
showers to most of the state. Brief to TEMPO MVFR conditions will
occur in those areas exposed to the low level flow, mainly over
mauka and north- and east-facing coastal sections.

An AIRMET for mountain obscuration is now in effect for all isles
except the Big Island. Also, an AIRMET for low level turbulence
is posted covering the area to the southeast through southwest of
the terrain for all islands.

&&

.MARINE...
The cold front over the eastern end of the state will hang up in
the vicinity of the Big Island today then slowly dissipate
tonight. Strong northeast winds will continue to affect the marine
area today and tonight with the strongest winds along and behind
the front. A Small Craft Advisory (SCA) is now in effect for all
of the Hawaiian coastal waters through Thursday, due to a
combination of strong winds and seas greater than 10 feet. High
pressure will build well to the north of the islands on Thursday,
shifting the winds around to a more typical east-northeasterly
trade wind direction. Moderate to locally strong easterly trades
are then expected across the marine area late in the work week
through early next week, with the strongest winds in the typically
windier waters around Maui and the Big Island.

The current large long-period north-northwest swell will hold
through the morning hours, then slowly decline this afternoon
through the end of the week. A High Surf Warning remains in
effect for exposed north and west facing shores of the smaller
island through 6 PM this evening. Advisory level surf will likely
continue for most of these areas through the day on Thursday, but
surf along west facing shores of Oahu may drop below advisory
levels by Thursday morning as the swell becomes more northerly.
The High Surf Advisory for north facing shores of the Big Island
is now in effect through 6 AM Thursday.

Surf is expected to drop below the winter time average along
north and west facing shores Friday through the weekend. A new
small to moderate northwest swell will be possible early next
week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

Wind Advisory until 6 AM HST Thursday for Lanai-Kahoolawe-Maui
Central Valley-South Big Island-Big Island North and East-Kohala.

High Surf Advisory until 6 AM HST Thursday for Big Island North
and East.

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

&&

$$

DISCUSSION...Gibbs
AVIATION...Kinel
MARINE...Jelsema

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