High Surf in Hawaii, November 13 to 15, 2016

Area Forecast Discussion
National Weather Service Honolulu HI
351 PM HST Sun Nov 13 2016

.SYNOPSIS...
Returning trade winds will become breezy to locally windy on
Monday and Tuesday as a strong surface high passes far north of
the state. Passing low clouds and showers will affect mainly
windward and mountain areas. Winds are expected to ease slightly
by the second part of the work week.

&&

.DISCUSSION...
Water vapor imagery shows a mid/upper level low several hundred
miles east of the Big Island, with a broad ridge over and west the
state. At the surface, a retreating ridge is located northeast
of the state, with a cold front over the far northwestern offshore
waters. A new high is located farther northwest behind the front.
Afternoon soundings from Lihue and Hilo show weak low-level
inversions around 4-5kft, with stronger elevated inversions around
7-9kft. Precipitable waters are 1.07-1.17 inches. MIMIC total
precipitable water imagery shows higher values around 1.3-1.4
inches over the windward waters, greatest north and east of the
Big Island. Even higher values over 1.6 inches are pooled far to
the north along the cold front.

Trade winds returned today, with gusty northeast winds across most
areas and clouds focused over windward sections of the islands.
Rainfall amounts have still been on the low side due to the dry
airmass and low inversions, with gages measuring only a few
hundredths of an inch over the past 12 hours. Upstream clouds have
thinned out during the afternoon, but clouds and showers are
expected to fill back in quickly this evening.

North of the area, the cold front currently over the northwestern
offshore waters will stall and being to dissipate on Monday. The
high far to the northwest will strengthen and pass north of the
area, tightening the gradient and leading to stronger trade winds.
Widespread breezy conditions are expected Monday/Tuesday. Models
show the high at peak strength late Monday/Monday night, but this
is just as the front is dissipating so we may not feel the full
impact of the winds associated with the high until Tuesday.
Depending on how quickly the front dissipates and the high builds
in, we could see a period of advisory-level winds through the
typically accelerated areas. Aloft, subsidence inversions
strengthen as a mid-level ridge builds just north of the state.
Clouds and showers will favor windward and mauka areas in more of
a typical trade wind weather pattern.

During the second half of the week the next low tracking across
the north Pacific will weaken the high and push it eastward. While
we will see winds drop off a notch as the ridge moves closer, it
won't be nearly as light as the past few days. A surface front is
expected to weaken north of the state with a new high building in
behind it late in the week. Extended models bring this front
closer to the islands before weakening, and we may at least see
an increase in moisture from it leading to a more of a wet trade
wind pattern for next weekend.

&&

.AVIATION...
VFR conditions will prevail across the state. Breezy trade winds
have replaced the light winds from the past several days, and AIRMET
TANGO has been issued for moderate low level turbulence lee of
the mountains. Passing showers and isolated MVFR ceilings will
affect windward and mountain areas.

&&

.MARINE...
The forerunners of a large northwest swell train reached Buoy 1 a
few hours ago and are expected to reach island shores this
evening. Surf is expected to peak tonight and early Monday
morning, then gradually diminish through Tuesday. Warning level
surf is expected on the smaller islands. As a result, a High Surf
Warning was issued early this morning for the north and west
facing shores of Niihau, Kauai, and Molokai, and the north facing
shores of Oahu and Maui beginning this evening. A high surf
advisory was issued for the west facing shores of Oahu and north
facing shores of the Big Island.

The large swell combined with strengthening trade winds will
produce hazardous seas in the exposed coastal waters so a Small
Craft Advisory has been issued for all coastal waters starting
this evening.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM HST Monday for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Olomana-
Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

High Surf Advisory until 6 PM HST Monday for Waianae Coast.

High Surf Advisory from midnight tonight to 6 PM HST Monday for
Big Island North and East.

Small Craft Advisory until 6 PM HST Monday for all Hawaiian
waters-

&&

Discussion...Bravender
Aviation...Morrison
Marine...Kodama