High Surf in Hawaii, March 5 to 7, 2017

Area Forecast Discussion
National Weather Service Honolulu HI
342 AM HST Sun Mar 5 2017

.SYNOPSIS...
Heavy showers with a few thunderstorms associated with a
weakening cold front is slowly advancing eastward over Maui County
this morning. As the front stalls and begins to dissipate later
today through Monday across Maui County, lingering moisture
combined with daytime heating and light winds will continue to
support heavy showers developing over the interior portions of the
central islands, especially this afternoon. Increasing rain
chances are expected to return across the state after mid-week as
another cold front and upper disturbance move over the region.

&&

.DISCUSSION...
A weakening cold front is forecast to stall and dissipate over Maui
County later today through early Monday. Light winds, plenty of
lingering low-level moisture (dewpoints remaining in the mid to
upper 60s) and daytime heating will support periods of heavy showers
remaining in the forecast. The best rain chances will remain across
the interior portions of the central islands (Oahu and Maui County)
this afternoon where the front is forecast to stall and dissipate.
Rainfall chances have been slightly lowered across Kauai and the
northwest waters through Monday night as a weak ridge noses north of
the island and light northerly flow and slightly lower dewpoints
setup.

The extended guidance remains in decent agreement through the week
and depicts the progressive pattern continuing as a series of
shortwave troughs dig southward across the central Pacific and carve
out an upper trough extending south across the region by mid week.
Falling upper heights, an attendant cold front dropping south toward
and over the state Monday night through mid week will support
another period of unsettled weather setting up over the state,
especially from Wednesday through Friday. Despite some model
differences being introduced through this extended portion of the
week, a fairly pronounced PV anomaly aloft and Q-G forcing for
ascent associated with the upper trough setting up over the region
will likely support the inclusion of thunderstorms in later packages
as confidence steadily increases (500 mb temps dipping into -12 to
17 deg C range are shown through this time). Forecast uncertainty,
however, remains high at this time with regard to any specifics with
location and timing this far out. In addition to the increasing
instability expected later in the week, periods of heavy
rain/flooding will also become a concern, if the current model
projections evolve as advertised.

&&

.MARINE...
A front will move slowly east over Maui County this morning
before stalling and beginning to dissipate later today and
tonight. Isolated thunderstorms and scattered showers have been
occurring along and ahead of this front. The threat of
additional thunderstorms is expected to diminish later today as
the front weakens.

The current west-northwest swell is producing combined seas of
near 10 feet over portions of the coastal waters surrounding
Kauai and Oahu. Therefore, a Small Craft Advisory (SCA) remains
in effect for these waters through tonight. Seas will gradually
lower by Monday, so the SCA will be lowered at the start of the
new work week. A new north-northwest swell will likely cause seas
to reach the SCA criteria again for parts of the coastal waters
starting late Wednesday, and continuing into Thursday. Winds are
expected to remain below the SCA threshold through the mid-week.

Surf produced by the west-northwest swell is expected to peak
later today or tonight, before gradually lowering on Monday. Surf
heights are forecast to be near the High Surf Advisory criteria
along exposed north and west facing shores of most islands,
Therefore, a High Surf Advisory remains in effect for north and
west facing shores of Niihau, Kauai, Oahu, and Molokai, north
facing shores of Maui, and west facing shores of the Big Island.
Looking ahead, a new north-northwest is expected to arrive late
Wednesday, peak Thursday, and then gradually lower on Friday. Surf
produced by this swell is expected to reach the High Surf Advisory
criteria along exposed north and west facing shores of the islands
Wednesday night and Thursday. Elsewhere, there will be a series of
small south and south-southwest swells through next weekend.

&&

.AVIATION...

A front over Molokai this morning will continue to drift east and
stall near Maui. The boundary will bring TEMPO MVFR conditions
with lower ceilings and showers, and a slight chance of a
thunderstorm, as it begins to dissipate. Spotty areas of MVFR
will occur behind and ahead of the front as well. VFR will hold
sway otherwise.

All AIRMETs have been discontinued. However, one for mountain
obscuration may be needed for Maui County later this morning if
lower ceilings persist as the front stalls.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Monday for north and west
facing shores of Niihau, Kauai, Oahu, Molokai, north facing shores
of Maui and west facing shores of the Big Island.

Small Craft Advisory until 6 AM HST Monday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Oahu Windward
Waters.

&&

Marine...Houston
Aviation...Kinel
Rest of Discussion...Gibbs