High Surf in Hawaii, August 7 to 9, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
321 AM HST Tue Aug 7 2018

.SYNOPSIS...
Expect a dry trade wind weather pattern with breezy winds today
with a strong high pressure system far to the north of the state.
A trade wind weather pattern remains in the forecast for much of
the state with scattered shower activity favoring windward and
mountain areas through the weekend. Hurricane Hector will be
passing into the Hawaii region later tonight through Thursday.
Wind speeds will trend higher across the state as Hector passes
south of the island chain. Enhanced shower activity remains in the
forecast for the eastern slopes of the Big Island for the same
time period. Hector will then exit the region by Friday, with a
return to typical summertime trade wind weather pattern for the
Big Island.

&&

.DISCUSSION...
A strong high pressure center far to the north of the Hawaiian
Islands will continue to produce breezy trade winds over the
state through much of the week. Trade winds will trend higher as
Hurricane Hector tracks south of the state starting later tonight
through Thursday. Large scale subsidence aloft will continue to
keep a strong trade wind inversion around 5000 to 6000 feet
elevation, capping cloud heights and limiting shower activity.
Scattered showers will remain limited to windward and mountain
areas with better chances for showers in the overnight hours.

Tonight through Thursday, the current forecast for Hurricane
Hector keeps the center of the storm passing south of the Hawaiian
Islands. Weather impacts for each island remains highly dependent
on Hector's track and intensity. Trade wind speeds will trend
higher as pressure gradients increase with Hector's passage to
the south. An area of deep tropical moisture associated with
Hector will produce an increase in rain showers over eastern
slopes of the Big Island, with the highest precipitation amounts
forecast over southeast sections of the Puna and Kau Districts as
surface winds become more southeasterly on Wednesday. Other areas
of the state may see little change in rainfall from current
levels. Please continue to closely monitor this strong hurricane
as it moves closer to the state. Tune into local TV and radio
stations, or go online to find the latest official forecasts
produced from the National Weather Forecast Office in Honolulu at
weather.gov/hawaii and the Central Pacific Hurricane Center at
weather.gov/cphc

Friday through Sunday, Hector will have exited the region. High
pressure north of the state will provide for a typical trade wind
weather pattern through the weekend. Clouds and passing showers
will tend to favor windward and mountain areas with most leeward
areas remaining dry through the weekend.

Volcanic emissions for the Kilauea volcano area will remain in a
trade wind flow pattern through Wednesday morning with any emissions
drifting southwest into the Kau district of the Big Island. By
Wednesday evening wind directions will likely shift towards the
southeast as Hurricane Hector passes by to the south of the Big
Island. These southeasterly winds will tend to push any emissions
towards the northwest up through Hilo and along the northern
slopes of the Big Island through Thursday. Easterly trade winds
are expected to return on Friday with any volcanic emissions
drifting back towards the southwest through the weekend.

The National Weather Service encourages everyone review their
hurricane preparedness plans. A guide for hurricane preparedness
can be found at www.ready.gov/hurricanes. The State of Hawaii and
each county also have preparedness information specific to the
islands available from Civil Defense websites.

&&

.AVIATION...
A surface high far northwest of the area will maintain locally
strong east winds and keep the atmosphere stable through the day
today. The strong winds and low temperature inversions may produce
turbulence to the lee of the mountains, so AIRMET Tango remains
in effect. VFR conditions will prevail, but there will be isolated
MVFR ceilings and visibilities, over mainly northeast sections of
the islands.

As Hurricane Hector moves closer to the area tonight, clouds
northwest of the hurricane will spread over the east side of the
Big Island and may produce widespread MVFR conditions there.
We may need to issue AIRMET Sierra for MTN OBSC on the Big Island
tonight.  Depending on the track Hector takes, thunderstorms
and IFR conditions could be possible.

&&

.MARINE...
A Tropical Storm Watch is in effect for the coastal waters south
of the Big Island Tuesday night through Wednesday. See the Marine
Weather Warning (MWWHFO) for details.

A Small Craft Advisory (SCA) remains posted for the typically
windier waters near Maui County and the Big Island into tonight.
Heading into tonight, when the waters south of the Big Island go
under the Tropical Storm Watch, a Gale Watch has been posted for
Alenuihaha and Pailolo Channels and Maalaea Bay. At that time, several
other coastal waters exposed to easterly swell have an SCA posted
for them for rising seas generated by Hurricane Hector swells.

A series of small south swells are expected through Wednesday. A
small north swell is expected to arrive late today, peak tonight
and Wednesday, then lower gradually Thursday and Friday.

Expect the swells generated by Hurricane Hector to gradually increase
through Wednesday, and this will result in increasing surf along
east facing shores of the Big Island and East Maui. A High Surf
Warning has been issued for the Big Island, and a High Surf
Advisory for Maui, both starting at noon today. As Hector moves to
the west and is south and southwest of the islands, the swell
will transition to a south swell.

Shorelines of the smaller islands will be less impacted as they
will be somewhat shadowed by the Big Island and Maui until Hector
moves further west. There will be a period of high astronomical
tides this week, so low lying coastal areas may have some coastal
inundation issues. Stay tuned for the latest updates on Hector and
its potential impacts on winds, seas, and surf across the area.

See the latest Oahu Surf Discussion (SRDHFO) for additional
details on surf and swell.

The 4 am Coastal Waters Forecast will be delayed to incorporate
information from the 5 am CPHC advisory package on Hurricane
Hector.

&&

.FIRE WEATHER...
Wind speeds will remain breezy today, especially down wind of
terrain, with gusts from 20 to 30 mph over mountain ranges and
through leeward valley areas. A drier and more stable air mass
will continue to limit shower activity across the state with
isolated to scattered showers lingering over windward and
mountain sections. Although critical fire weather thresholds will
likely not be crossed during the next couple of days, many of the
ingredients will remain in place for elevated fire activity.
Hurricane Hector will be crossing through the region from tonight
through Thursday. Trade wind speeds will trend higher as the
system passes to the south of the state from tonight through
Thursday. Enhanced rain showers, locally heavy at times, will
develop along eastern slopes of the Big Island through the same
time period.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Tropical Storm Watch for Big Island.

High Surf Warning from noon today to 6 PM HST Wednesday for
South Big Island-Big Island North and East.

High Surf Advisory from noon today to 6 PM HST Wednesday for
Windward Haleakala.

Small Craft Advisory until midnight HST tonight for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Tropical Storm Watch for Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory from midnight tonight to midnight HST
Wednesday night for Oahu Windward Waters-Kaiwi Channel-Maui
County Windward Waters-Big Island Windward Waters.

Gale Watch from late tonight through Wednesday evening for
Maalaea Bay-Pailolo Channel-Alenuihaha Channel.

&&

DISCUSSION...Bohlin
AVIATION...Donaldson
MARINE...M Ballard
FIRE WEATHER...Bohlin