High Surf in Hawaii, February 13 to 14, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
331 AM HST Thu Feb 13 2020

.SYNOPSIS...
A departing trough of low pressure and a building high northeast
of the state, will bring a gradual return of trade wind weather to
the islands over the next couple days. Showers will favor windward
locales with a few showers reaching leeward areas at times. Drier
conditions and moderate to breezy trade winds are expected by the
weekend, with these conditions continuing through the middle of
next week. Showers will continue to favor windward and mauka areas
with a stray shower spilling leeward from time to time.

&&

.DISCUSSION...
Currently at the surface, a weakening trough of low pressure is
located a few hundred miles west of Kauai, while a 1033 mb high
is centered around 1500 miles north-northeast of the island
chain. Meanwhile, a new cold front is located around 900 miles
west-northwest of Kauai. Aloft, an upper level low is evident in
water vapor imagery several hundred miles southwest of the Big
Island. Light to moderate trade winds prevail over the western
islands early this morning, while moderate to breezy east-
southeasterly winds prevail over the eastern islands. Infrared
satellite imagery shows clear to partly cloudy skies in most
areas from Kauai to Maui, with mostly cloudy conditions over the
Big Island and southeast sections of Maui. Radar imagery shows
scattered showers moving into windward areas, with mostly dry
conditions in leeward locales. Main short term focus revolves
around rain chances and the gradually strengthening trades.

The surface trough will continue to shift westward over the next
couple days, as a weakening cold front approaches from the west.
These two features will then merge several hundred miles northwest
of the state by Friday evening. Meanwhile a broad surface high
will hold in place far to the northeast of the island chain. The
gradient will remain a bit weaker over the western islands through
the remainder of the work week, with moderate trade winds
prevailing, while breezy trade winds return to the eastern end of
the state beginning today. As the front fizzles out northwest of
the islands Friday night and Saturday, breezy trade winds will
begin to fill back in over the western end of the state. Only
minor fluctuations in trade wind strength are then expected
through the remainder of the weekend and into the middle of next
week.

Winds at the higher elevations of the Big Island and Maui will be
quite strong through the morning hours and possibly into the
early afternoon. As a result, a Wind Advisory is in effect through
6 PM this evening for the Haleakala Summit, the Big Island
Summits, as well as the Big Island interior.

Scattered windward showers are expected to continue today, with a
shower or two possibly reaching leeward areas. Model solutions
then show a band of deeper moisture moving over the islands
tonight and Friday, and this will likely increase windward shower
activity and result in more leeward spillover. The airmass will
then dry out quite a bit Friday night through Saturday night as
mid and upper level ridging builds over the state and precipitable
water values plummet. Persistent trade winds should bring a
gradual increase in trade showers by Sunday, with fairly typical
trade wind weather prevailing through the middle of next week.

&&

.AVIATION...
A trough of low pressure west of the Hawaiian Islands will keep
unsettled weather in the short range forecast. For today expect
brief periods of showers for most islands favoring the morning
hours with higher chances for showers along the east and
southeastern sections of Maui and the Big Island. Large scale
winds will shift from southeasterly to a more easterly direction
today through Friday as the trough moves away from the island
chain and high pressure builds back in over the state. More
typical windward showers will return across the eastern islands
today and over all islands by Friday. MVFR conditions are possible
for eastern slopes of most islands and likely for the east and
southeastern sections of the Big Island later this afternoon and
evening due to enhanced shower activity.

AIRMET Tango in effect for tempo moderate turbulence from Molokai
eastward to the Big Island below 100 west through north of
mountains. SIGMET TANGO will continue for upper level moderate to
severe turbulence across all islands. These turbulent conditions
will likely continue through the morning hours. AIRMET Sierra for
tempo mountain obscuration may be needed for the Big Island and
Maui later this afternoon.

&&

.MARINE...
A weakening surface trough west of the state will continue west
and southwest away from the area through the weekend as high
pressure builds far northeast of the island chain. This will lead
to strengthening trade winds, with strong to near-gale force
winds possible this weekend into early next week. With the trades
and the concomitant increase in wind waves expected today, the
Small Craft Advisory (SCA) was expanded to include most coastal
zones, except for a few leeward areas. Stronger trades, along with
a new moderate to large northwest swell, will likely bring SCA
conditions to most, if not all, marine zones no later than this
weekend.

The current mid-period north swell and long-period northwest
swell will continue to steadily decline, with small northwest
swells today and Friday. A larger northwest swell is forecast
over the weekend, bringing near-advisory level surf to some north
and west facing shores as it peaks Sunday. This swell will
gradually decline through the first half of next week.

Surf along exposed east facing shores will receive a notable boost
into the weekend as trade winds return over and upstream of the
islands. Latest guidance shows advisory level surf through tonight
along east facing shores, so a High Surf Advisory remains in
effect for most east facing shores. East shore surf will likely
drop just below the advisory level by Friday, but remain elevated
through the weekend. Surf along south facing shores will remain
small with mainly background swells, aside from a couple moderate-
size south swells possible this weekend and early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for Kauai Windward-Oahu
Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Wind Advisory until 6 PM HST this evening for Haleakala Summit-
Big Island Interior-Big Island Summits.

Small Craft Advisory until 6 AM HST Friday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Channel-Oahu Windward Waters-
Kaiwi Channel-Maui County Windward Waters-Pailolo Channel-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

&&

DISCUSSION...Jelsema
AVIATION...Bohlin
MARINE...Kinel