High Surf in Hawaii, November 20 to 30, 2016

Area Forecast Discussion
National Weather Service Honolulu HI
337 AM HST Sun Nov 20 2016

.SYNOPSIS...
High pressure north of the state will keep a moderate to breezy
trade wind flow in place through early next week. The trades will
strengthen Tuesday through the Holiday weekend, with breezy to
windy conditions expected across the island chain. Clouds and
showers will favor windward and mauka areas through the period,
with showers occasionally reaching leeward locales due to the
strength of the trades.

&&

.DISCUSSION...
Currently at the surface, a 1029 mb high centered around 900
miles north-northeast of Honolulu, continues to drive the breezy
trade winds across the island chain early this morning. Meanwhile
closer to home, a remnant band of moisture associated with an old
front remains over the western islands, and over and upstream of
the eastern half of the state. Infrared satellite imagery shows
a combination of high and low cloudiness, resulting in mostly
cloudy conditions in most areas. Radar imagery shows scattered to
numerous showers moving into windward areas, with some of the rain
periodically reaching leeward areas due to the strength of the
trades. Main short term concern revolves around rain chances.

Today,
High pressure north of the state will shift steadily off to the
southeast through the day, keeping a breezy trade wind flow in
place across the island chain. The band of moisture associated
with the old frontal remnants will slide south of the western
islands later this morning, but will remain over the eastern half
of the state through the day, keeping windward sections of the Big
Island and Maui rather wet. Meanwhile, on Oahu and Kauai, coverage
of showers should be on the decrease this morning, with
noticeably less shower activity expected by this afternoon. Even
in areas where the shower coverage decreases, considerable
cloudiness is expected to remain in place through the day due to
jet cirrus streaming overhead.

Tonight through Monday night,
High pressure off to the northeast of the state will weaken
slightly, allowing the trade winds to ease just a bit. The band of
enhanced moisture over the eastern end of the state will lift back
northward into Oahu and Kauai tonight, then linger over the
entire island chain through Monday night. Additionally, a weak
upper level disturbance will move overhead tonight, helping boost
inversion heights and resulting in an increase in deep layer
moisture with precipitable water (PW) values rising into the 1.4
to 1.7 inch range. The upper level disturbance will lift
northeast and away from the area Monday and Monday night, but PW
values will remain in the 1.5 to 1.7 inch range. As a result, we
should see an extended period of wet trades across the island
chain, with slightly higher rainfall amounts expected through the
period given the increase in deep layer moisture. Showers will
favor windward and mauka areas, with some of the shower activity
reaching leeward areas from time to time.

Tuesday through next Saturday,
Medium range guidance is in fairly good agreement through
Thanksgiving day, with some minor differences noted by the end of
the week and into the upcoming weekend. Overall, strong high
pressure will build north of the state on Tuesday, and remain
centered north of the island chain into next weekend. This will
result in a strengthening of the trade winds, with breezy to windy
conditions expected Tuesday into the Holiday weekend. In fact, the
winds may reach advisory levels at times across portions of the
state. As for sensible weather details, bands of enhanced moisture
will continue to rotate through the islands on the southern
periphery of the deep layered ridge north of the state. This
should keep a wetter than normal trade wind pattern in place
through the period. Showers will continue to favor windward and
mauka areas, but with the strong trades, some of the showers will
periodically reach leeward areas as well.

&&

.AVIATION...
Showery low cloud remnants from an old front continue to sweep
across the state from the east. MVFR conditions, and possibly
isolated IFR, will be concentrated over windward coastal, and
windward-facing mauka and upslope sections of each isle. As the
line of cloudiness gradually drifts south, most of the moisture by
the later morning hours today will mainly affect the chain east
of Oahu. AIRMET Sierra for mountain obscuration is currently in
effect for the north through east slopes of all the islands.

AIRMET Tango remains posted for low level turbulence to the lee of
the mountains, all islands, as breezy trade winds persist.

&&

.MARINE...
The Small Craft Advisory (SCA) remains in effect for most Hawaiian
coastal waters through tonight due to a combination of strong trade
winds and rough seas. An overnight ASCAT pass reflected this and
showed 20 to 30 kt over the islands, with the highest winds in the
channel. Winds will weaken slightly later tonight and Monday, which
should allow the winds and seas to drop slightly below advisory
levels across the Kauai waters and the leeward Oahu and Maui County
waters.

The latest model guidance remains in good agreement over the next
several days and depicts the subtropical ridge axis becoming
oriented from east to west over the eastern Pacific. A large batch
of strong easterlies extending from the west coast to the islands by
mid week will be expected. A combination of the locally generated
seas and trade wind swell will translate to advisory-level surf
along east facing shores as early as Monday night, which should
persist through the rest of the week. SCA conditions will likely be
expanded to all coastal waters by Tuesday due to a combination of
winds and seas. In some of the channels, winds will approach gale
force levels Tuesday through Wednesday, then reach gale strength
beginning as early as Thursday.

Surf along north and west facing shores will remain below advisory
levels all week. Small northwest swells are expected Tuesday through
Wednesday and Friday through Saturday.

Recent activity across the Tasman Sea may result in a slight
increase in surf along the southern shores by the mid-week period
due to a small south-southwest swell. Another gale is forecast to
setup southeast of New Zealand through the early portion of the
upcoming week, which could translate to another small southerly
source by the end of next weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Monday for Oahu Windward
Waters-Kaiwi Channel-Maui County Windward Waters-Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-
Big Island Leeward Waters-Big Island Southeast Waters.

Small Craft Advisory until 6 AM HST Monday for Oahu Leeward
Waters-Maui County Leeward Waters.

&&

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