High Surf in Hawaii, July 13 to 19, 2022

Area Forecast Discussion
National Weather Service Honolulu HI
344 AM HST Wed Jul 13 2022

.SYNOPSIS...
Breezy trade winds will continue through the upcoming weekend,
with clouds and showers favoring windward and mauka locations.
Shower coverage has increased overnight, which will persist today
as remnant moisture from former Tropical Cyclone Bonnie moves
through. Another surge in moisture and winds is expected this
weekend as the remnants of Hurricane Darby pass south of the Big
Island.

&&

.DISCUSSION...
Satellite-derived precipitable water showed a surge in moisture
associated with the remnants of former Tropical Cyclone Bonnie
moving through this morning. Peak rainfall totals over the past
12-hrs (as of 2 AM HST) reflects this with values hitting the 2
to 3 inch range. A combination of breezy trades, enhanced
moisture, and the trade wind inversion now up to 10,000 ft
supports a wet trade wind pattern continuing today. Some showers
will make it into our dry leeward areas periodically.

Once the remnant moisture associated with Bonnie shifts away from
the area tonight through Friday, the focus will turn to Hurricane
Darby, which is currently located about 1400 miles east-
southeast of Hilo. As Darby enters the central Pacific basin
tonight into Thursday, a combination of cooler waters, mid-level
dry air, and increasing shear will translate to a weakening trend
as it approaches the state. The latest forecast from the National
Hurricane Center reflects this and has Darby degenerating into a
trough by the end of the weekend as it passes by to the south.
Despite the weakening trend, strong trades along with plenty of
moisture accompanying this feature moving through will translate
to another wet and windy pattern for the islands -- beginning as
early as Friday night for the eastern end of the state.

&&

.AVIATION...
A high pressure system far north of the region will keep moderate
to breezy trade winds in the forecast. Deep tropical moisture,
from former Tropical Cyclone Bonnie, is spreading westward across
the islands today. Expect enhanced scattered to numerous showers
with this rising tide of moisture. Periods of MVFR/IFR conditions
are forecast over windward airfields for the next 24 hours.
Leeward site will also see passing showers with brief MVFR
conditions possible.

AIRMET Sierra remains in effect for mountain obscurations over
windward and mountain slopes of the Big Island, Maui, Lanai,
Molokai, Oahu and Kauai for elevations above 2000 feet due to low
clouds and showers. This AIRMET will decrease in coverage later
this morning.

AIRMET Tango remains in effect for moderate low level turbulence
over and downwind of all island mountains. This AIRMET will likely
continue through Thursday.

&&

.MARINE...
A somewhat active period is expected in Hawaiian waters over the
next week or so. Strong high pressure to the N will ensure that
fresh to strong trade winds will prevail, with surges to near-
gale force in the channels. In addition, a pair of solid S swells
are expected to produce Advisory-level surf along S facing shores.
Also, moisture associated with the remnants of Bonnie will move
through the area today, with what is expected to be a weakening
Post-Tropical Remnant Low Darby passing S of the islands this
weekend. Extreme high tides the next couple of afternoons may lead
to salt-water flooding of low-lying shoreline areas.

Barely discernible remnants of Bonnie, in the form of increased
showery low clouds, will support an increase in trade wind speeds
and showers as it moves W over the area through tonight. A Small
Craft Advisory (SCA) is in effect for a majority of the area.
Trade winds speeds may briefly ease a little thereafter, but
another surge in wind speeds and gusty showers are possible this
weekend as what is now Hurricane Darby weakens to a Post-Tropical
Remnant Low and dissipates while passing S of the Big Island.
Greatest chance of increased winds, seas and showers with Darby
will be over Big Island waters.

Buoy observations indicate that surf along S facing shores will
be on the rise today, as long-period energy that had been observed
at buoy 51004 is now also being observed at buoy 51002. A High
Surf Advisory has been issued through Thursday for S facing shores
of all islands. Surf will ease a little late Thursday into Friday,
but will be reinforced with a larger, longer period (20-22 sec) S
swell late Friday through the weekend. Peak surf heights with
this second swell will easily reach HSA criteria (10 foot faces),
with potential for surf to reach High Surf Warning levels along S
shores (15 foot faces).

Surf along E facing shores will remain elevated and rough through
the week. A small, 10-12 sec period ESE swell will also move
through the next couple of days, but greatest contribution to
seas will be from the short-period trade wind swell. Swells
generated by Darby are expected to add to the mix this weekend,
and will probably be biggest along E facing shores of the Big
Island, where a High Surf Advisory may be required.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Thursday for Niihau-Kauai
Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kauai
South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Southeast-
Molokai Leeward South-Lanai Leeward-Lanai South-Maui Central
Valley South-Kipahulu-South Maui/Upcountry-South Haleakala-Big
Island South-Big Island Southeast.

Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Thursday for Oahu Leeward
Waters-Kaiwi Channel-Maui County Windward Waters.

&&

DISCUSSION...Gibbs
AVIATION...Bohlin
MARINE...Birchard