High Surf in Hawaii, January 9 to 10, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
332 AM HST Wed Jan 9 2019

.SYNOPSIS...
Mostly dry conditions along with light winds will prevail across
the state through the second half of the week and upcoming
weekend. The best rainfall chances will remain over windward
sections from Oahu to the Big Island through Thursday where
remnant moisture associated with an old frontal boundary and light
trades exist. Daytime sea breezes and overnight land breezes will
overpower a rather weak trade wind flow elsewhere each day.

&&

.DISCUSSION...
The latest surface analysis and satellite imagery showed the
subtropical ridge near the islands (southward of its typical
position), a front extending southwest near Midway tracking eastward
and a band of low clouds associated with an old frontal boundary
lurking near/over Maui County and the Big island. This band of
moisture combined with light background easterly flow will support
the best rainfall chances over windward locations from Oahu to
the Big Island into Thursday, especially overnight through the
early morning hours. Elsewhere, mostly dry conditions will prevail
with daytime sea breezes and overnight land breezes continuing.

No significant changes are anticipated Friday into the upcoming week
as the progressive pattern characterized by a series of fronts
passing north of the state persists. Light winds giving way to
daytime sea breezes and overnight land breezes will continue over
much of the state as the ridge remains in the area and the
gradient remains weak. The exception will be over the eastern end
of the state where light to moderate trades will support windward
showers. Accumulations, however, should remain light due to the
dry and stable conditions associated with a strong ridge holding
aloft.

&&

.AVIATION...
A weak front northwest of the Islands should help to maintain
light flow across the region today. After 21Z this afternoon, sea
breezes will dominate, replaced once again by land breezes after
sun down.

A band of increased low level moisture continues to push westward
over the area which has led to an uptick in shower activity.
Iso/Sct showers are forecast to mainly affect the windward slopes
and coasts through this afternoon periodically lowering
visibility. Otherwise, VFR conditions prevail.

&&

.MARINE...
Low pressure systems moving rapidly eastward across the north
Pacific will provide weak easterly to variable winds across the
state through the end of the week.

The lows will direct small to moderate northwest swells towards
the islands through Friday. In addition, a long period moderate to
large north-northeast swell will build through this morning, peak
in the afternoon and evening, then decline Thursday and Friday.
As the swell builds, it will cause seas to reach the Small Craft
Advisory (SCA) threshold across exposed windward waters and
channels today, so the SCA has recently been put into effect. And
since the swell has an easterly component, surf heights will reach
the High Surf Advisory (HSA) level along east facing shores. The
HSA has already been posted for east facing shores, and extends
through tonight. In addition, moderate harbor surges may develop
due to this swell in some north facing harbors, such as at Hilo
and Kahului. A Marine Weather Statement has been posted for
windward Maui and Big Island waters highlighting the harbor surge
potential. Surf conditions along north facing shores have been
left out of the HSA for the time being as face heights are
expected to be just below advisory criteria.

A new large northwest swell will spread across the waters
adjacent to the western end of the island chain late Friday night.
This swell will likely increase seas above the SCA threshold
across exposed waters from Saturday through Sunday. Surf is also
expected to be near the High Surf Warning criteria along most
north and west facing shores of the smaller islands this weekend.
Since this swell has some westerly component, surf may approach
the High Surf Advisory criteria along west facing shores of the
Big Island starting late Saturday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Thursday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-Big Island North and East.

Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Alenuihaha Channel-Big Island Windward Waters-Big Island
Southeast Waters.

&&

DISCUSSION...Gibbs
AVIATION...Thomas
MARINE...Kinel