High Surf in Hawaii, June 16 to 17, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
344 AM HST Sat Jun 16 2018

.SYNOPSIS...
Trades are forecast to remain light into next week, potentially
allowing land and sea breeze conditions to setup over leeward areas
each day. Although shower coverage will continue to focus over
windward and mauka areas, shower development will also become a
possibility across the interior areas of the smaller islands through
the afternoon periods as sea breezes develop. Volcanic emissions
from the Kilauea volcano will shift back toward the smaller
islands today for a brief period in response to the lighter
winds.

&&

.DISCUSSION...
Short-term (through Sunday) guidance remains in good agreement and
depicts the subtropical ridge holding near or just north of the
islands due to a series systems moving through across the central
Pacific. This ridge in proximity to the islands has translated to
the trades relaxing, which will support localized land and sea
breezes developing over leeward areas each day. Although showers
will continue to favor windward areas as the light trades hold,
some development across leeward areas will be possible through the
afternoon/evening hours as sea breezes setup. Near average PWs,
however, may limit the overall shower coverage.

Extended (Monday through Friday) guidance remains in decent
agreement and depicts no significant changes through Wednesday as
the weak ridge of high pressure remains near the islands. Trades
will remain light with localized land and sea breezes remaining
possible each day. The best source of low-level moisture is depicted
over the western end of the state. Model PWs increase into the 1.5-
1.8" range, which is well above normal for this time of year. As a
result, the best shower coverage will most likely setup over these
western areas through the afternoon periods as sea breezes develop.
Guidance suggests a return of moderate to breezy trades through the
second half of the week as the ridge begins to shift back toward the
north.

Volcanic emissions from the Kilauea volcano is forecast to creep
northward toward the smaller islands through the day today due to
the light winds and low-level flow (up to 10 kft) out of the
east-southeast direction. Guidance, however, depicts the low-
level flow shifting back out of the northeast and increasing
Sunday into next week, which should favor the volcanic emissions
shifting back toward the south of the smaller islands.

&&

.AVIATION...
An area of clouds and embedded showers over the Big Island earlier
in the evening, has divided into three parts, where one part is
moving northwest across the windward waters, the other part is
moving across the leeward waters, and the middle part is breaking
up across Maui and the Big Island. There are a few showers with
these clouds, but not much, with tops between 10 and 15k feet.

Surface analysis has a weak low level trough in the Kaiwi
Channel that will interrupt the trade wind flow around Molokai,
Lanai, and Oahu today, with the winds becoming light and variable
later this morning. Precipitable water is around 1.45 inches. With
this piece of data, plus a trough, light wind, and ample sunshine,
expect a tad more showers over interior and lee areas of Oahu
Molokai, and Lanai this afternoon. AIRMET Sierra is not out of
the question especially for these islands this afternoon.

The low level inversion is expected to be stronger elsewhere, so
showers could be less as well as being less intense.

&&

.MARINE...
A weak ridge of high pressure will remain nearly stationary
around 150 nm N of Kauai through the weekend, keeping light to
locally moderate trade winds in place across the marine area. A
dissipating front will sag southward and close to Kauai early next
week, weakening the ridge and potentially diminishing the winds
further.

The current S swell is expected to peak just below advisory
levels along S facing shores today, then slowly decline through
Monday. Only small S shore surf is expected Tuesday through the
end of next week.

A pair of long-period WNW swells will peak today, with a slow
decline through early next week. Only small north shore surf is
expected Tuesday through the end of next week.

The combination of long period S and WNW swells is expected to
push surf heights to the advisory level of 8 feet along W facing
shores of the Big Island today and tonight. As a result, a High
Surf Advisory (HSA) has been issued for this area. We will
continue to monitor observations closely, as the HSA may
eventually need to be extended through Sunday by later shifts.

Short-period trade wind swell will remain small through the
middle of next week. A small long-period E swell associated with
former E Pacific hurricane Bud, may bring a small boost to surf
along E facing shores today through early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Sunday for Kona-Kohala.

&&

SYNOPSIS/DISCUSSION...Gibbs
AVIATION...Lau
MARINE...Jelsema