High Surf in Hawaii, November 9 to 10, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
953 AM HST Sat Nov 9 2019

.SYNOPSIS...
Local land and sea breezes will prevail through tonight as a
front approaches from the northwest. Clouds and showers will favor
mauka areas during afternoon and evening hours. A new high will
build north of the area Sunday through early next week, allowing
trade winds to return. Clouds and passing showers will then favor
windward and mauka areas. Winds will decrease toward the end of
the week as another front approaches the area.

&&

.DISCUSSION...
A weakening front just northwest of Kauai continues to keep winds
light across the area as the supporting upper trough triggers
bouts of deep convection. Satellite imagery shows mostly cloudy
skies over Kauai and Oahu, with clear to partly cloudy skies noted
elsewhere. Radar shows scattered showers moving into Kauai, with
isolated showers in the vicinity of Maui County and the Big
Island. The front will stall over or near Kauai tonight and
Sunday. Light winds will prevail through tonight, with daytime sea
breezes and overnight land breezes expected. A new high will
build north of the islands Sunday bringing a return of light to
moderate trade winds. The light to moderate trades will hold in
place through Wednesday, before easing and shifting to the south
and southeast late next week as a new cold front approaches from
the northwest.

A convective pattern is expected through Sunday, with showers
favoring mauka areas during the day and coastal areas at night.
Shower coverage will be greatest across Kauai today where the
deepest moisture and best forcing will reside. The forecast was
altered for the possibility for isolated thunderstorms across
Kauai and surrounding waters this morning. The threat for
thunderstorms should diminish as the front weakens and the
supporting upper trough lifts northward. A typical windward
focused shower pattern will resume Sunday night as trades return,
with trade winds continuing through Wednesday. Easing and shifting
trade winds during the latter part of next week could bring an
increase in interior and leeward showers during the day, with
showers favoring windward slopes and coasts at night.

A Wind Advisory remains in effect for the Big Island summits
through this afternoon due to strong winds aloft associated with
the upper trough. Winds are expected to subside below advisory
thresholds by this evening.

&&

.AVIATION...
Light and variable winds will continue through tonight due to a
front approaching from the northwest. Shower coverage will continue
mostly over and around Kauai ahead of this boundary, with some
possibly making it into Oahu as well. Another area of moisture
approaching from the southeast will likely translate to increasing
cloud and shower coverage over and around the Big Island later
today. MVFR CIGS/VSBY is possible with any showers that develop.
Although confidence remains low at this point, an AIRMET for mountain
obscuration for these areas can't be ruled out as conditions evolve.

Elsewhere, the light winds will allow local sea breezes to develop
this afternoon with cloud buildups and possible light showers over
interior areas. Land breezes will clear out the eastern end of the
state overnight.

An upper-level trough nosing towards Hawaii may provide some light
to moderate upper-level turbulence, along with some passing high
clouds, over the islands today.

&&

.MARINE...
The combination of a weak surface front and a strong trough aloft
has led to the (somewhat unexpected) development of a few heavy
showers over Kauai waters this morning, with a few lightning
strikes detected, prompting a forecast update. With the trough
aloft moving rapidly E, the expectation is that the potential for
additional thunderstorms will diminish later today. The surface
front is so poorly defined near the islands that it is difficult
to identity, and features little in the way of a wind shift. Light
and variable winds will become light easterly trade winds tonight
and Sunday as a weak surface high passes N of the islands. These
trade winds, at times locally moderate, will persist through
midweek before diminishing once again as another front approaches.
Winds and seas will remain below Small Craft Advisory levels
through Wednesday.

Long-period forerunners of a building S swell are currently
arriving in island waters, and it may produce peak surf heights
near the S shore High Surf Advisory level (HSA) on Sunday. Will
continue to monitor local buoy observations to determine the need.
A relatively small NNW swell will build today and peak tonight,
with another slightly larger NNW swell expected Monday. Peak surf
heights with both swells are expected to remain below HSA levels.
A larger NW swell may arrive around Thursday, with initial
indications that this will produce HSA-level surf along exposed N
and W facing shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST this evening for Big Island Summits.

&&

DISCUSSION...Powell
AVIATION...TS
MARINE...Birchard