High Surf in Hawaii, December 9 to 10, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Sat Dec 8 2018

.SYNOPSIS...
A weakening front near Maui County will advance to the Big Island
through Sunday then stall and dissipate, bringing showery weather to
the eastern islands. Rather brisk trade winds will prevail through
the upcoming work week, with showers focusing over windward and
mountain areas while reaching the lee areas of the smaller islands
at times.

&&

.DISCUSSION...
A rather diffused frontal cloud band is over the Maui County this
evening, bringing showers to mainly windward Maui and Molokai. This
weakening front will eventually sag to the Big Island on Sunday and
dissipate. Moisture associated with this front will continue to
affect mainly the eastern islands. Latest satellite imagery showed
another band of low clouds currently near Kauai. This band of low
clouds will advance south, reaching the northern islands overnight
into Saturday, and thereby providing some showers as well. Most of
the showers will be focused over windward and mauka areas of the
islands under the trades, with some showers reaching the lee areas
of the smaller islands under the strong winds.

A surface high pressure about 800 nm northwest of the islands is
providing the rather brisk trade winds to the area. A Wind Advisory
remains in effect for the typically windier areas of Maui County and
the Big Island through Sunday. As this high will be passing north of
the islands in the next couple of days, the rather strong winds will
persist across the area. Thus, the Wind Advisory may need to be
extended. The trades may ease slightly by the middle of next week,
as another front is forecast to pass north of the state. But then,
forecast solutions indicated another high pressure may pass far
north of the islands toward the later half of next week, thus
providing more brisk trade winds to the area.

In all, trade wind weather with robust winds will prevail across the
state through the upcoming work week.

&&

.AVIATION...
A weakening front is moving slowly south, down the island chain, and
is mainly affecting Maui County this evening with showery low clouds
(and MVFR conditions). The front will begin more directly affecting
the Big Island later tonight. Trade winds are breezy to strong
across the area as robust high pressure passes north of the Aloha
State.

AIRMET Sierra is currently posted due to mountain obscuration across
windward areas of Maui County. Conditions will gradually improve
from west to east this evening and overnight but will likely spread
down to windward sections of the Big Island overnight. Airmet Tango
is currently posted both for low level turbulence south and west of
mountain ranges as well as for strong surface winds around portions
of Maui County and the Big Island.

&&

.MARINE...
High pressure currently centered far NW of the islands will track
slowly E over the next several days, and strengthen slightly as it
passes N of the islands on Monday. The high will support open ocean
trade wind speeds between 20-25 kt near the islands. These NE to ENE
winds will accelerate around the island terrain to the point that
windier marine zones around Maui and the Big Island may see winds
near gale force. Latest guidance indicates the most likely time for
this to occur will be from Sunday night into Monday night, but
hi-res guidance is not in agreement that it will occur, reducing
confidence to the point that a Gale Watch will not be issued at this
time. In the meantime, a Small Craft Advisory (SCA) is in effect for
all waters due to the strong trades and combined seas, and will
likely be required for most of the week.

Surf and combined seas will be on the increase tonight as a new NNW
swell arrives, with long-period forerunners already being detected
at buoys 51001/51101 NW of Kauai. This swell will peak on Sunday
with open ocean swell heights expected to be near 12 feet. A High
Surf Warning is posted for exposed north and west facing shores,
with a High Surf Advisory (HSA) posted for the west facing shores of
Oahu, where greater swell shadowing is expected. A HSA is also
posted for E facing shores of most islands due to strong trades
driving an increase in short-period wind waves, with surf expected
to remain elevated for most of the week. Lastly, a Marine Weather
Statement (MWS) has been issued to draw increased attention to the
potential for harbor surges, especially in Hilo and Kahului harbors.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 AM HST Monday for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Molokai-Maui
Windward West-Maui Central Valley-Windward Haleakala-Big Island
North and East.

High Surf Advisory until 6 AM HST Monday for Waianae Coast-
Olomana-South Big Island.

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

Small Craft Advisory until 6 PM HST Tuesday for all Hawaiian
waters.

&&

DISCUSSION...Hui
AVIATION...Kinel
MARINE...Birchard