High Surf in Hawaii, July 5 to 8, 2021

Area Forecast Discussion
National Weather Service Honolulu HI
339 AM HST Mon Jul 5 2021

.SYNOPSIS...
Trade winds will persist through the rest of the week, although
the trades will trend down from locally strong to moderate speed
around mid week. This is the result of the weakening of the surface
high centered far north of Kauai. Locally breezy trades will
return over the weekend as the high strengthens north and
northeast of the islands. Showers will continue to favor the
windward and mauka areas, with higher frequency of these showers
coming during the nights and mornings.

&&

.DISCUSSION...
The moderate to locally breezy trades are currently being
sustained by a weakening 1032 mb surface high located 1130 miles
north- northwest of Kauai. This high will dissipate in the next 24
and be replaced by a new 1037 mb high located further north and
west from the current high. In response, the locally strong trades
will trend down to moderate speed by Thursday. It will hold at this
strength to until Friday night or Saturday where trades will get a
fresh boost to locally strong as the high drops south and closer
to the islands.

The slightly weaker trade winds in the coming days may favor some
locally daytime sea breeze over the west end of the smaller
islands, leading to some spotty afternoon showers. Otherwise, the
moderate trades will continue to usher some scattered showers into
the windward and mountain areas. The frequency of these trade
showers will be highest during the overnight and early morning
hours. Mid level ridging over the islands is strong and will
persist through the week, thus maintaining ordinary trade showers.

Current satellite imagery shows the pool of moisture that moved
into Kauai late yesterday afternoon continuing to exit Kauai
County. We anticipate the bulk of these clouds and showers to be
west of Kauai shortly after sunrise. During the evening hours,
ending at 2 am HST, rain gages across the lower elevations of
windward Kauai pickup an average of a quarter inch. The highest
amount recored was at North Wailua with 1.35 inches.

On Oahu, the showers eased up after 10 pm HST, joining the rest
of the islands with limited trade showers. Satellite imagery shows
an area of potential scattered showers, however, just upwind of
windward Big Island. Models suggest scattered showers for windward
Big Island and Maui later this morning, continuing into this
afternoon. There should be more sunshine for Kauai and Oahu
today, especially over on the south and lee side of the islands.

&&

.AVIATION...
High pressure north of the state will keep moderate to locally
breezy trade winds in place through today and tonight. A band of
enhanced moisture is moving through Kauai early this morning,
bringing more frequent showers along with some reduced cigs/vsbys
to windward slopes and coasts. Low clouds and showers are more
sparse over windward sections from Oahu eastward to the Big
Island. Drier conditions should develop over windward areas of
Kauai later this morning, with VFR conditions then prevailing
through the remainder of the day. Elsewhere, predominantly VFR
conditions should prevail during the next 24 hours.

AIRMET Sierra remains in effect for windward sections of Kauai.
Conditions should improve here later this morning.

AIRMET Tango remains in effect for low level turbulence over and
downwind of the terrain of all islands. This AIRMET will likely
continue through the day.

&&

.MARINE...
A strong surface high pressure system centered far north-
northwest of the islands will maintain locally strong trade winds
across the state into the middle of this week. As a result, a
Small Craft Advisory (SCA) remains in effect for the typically
windier waters adjacent to the islands of Maui County and the Big
Island through Wednesday afternoon. The surface high will drift
slowly northwest during the next few days, so the latest forecast
indicates the trade winds will weaken slightly by Thursday.

A long-period south-southwest swell continues to spread up across
the area early this morning. Recent observations from the
nearshore buoys along the south shores show the swell height is
around 4 feet with a wave period of approximately 18 seconds. This
swell will continue to build through tonight, and then will
likely peak on Tuesday, followed by a slow downward trend from
Tuesday night through Wednesday. As a result of the elevated surf
produced by this swell, a High Surf Advisory (HSA) is in effect
for the south facing shores of all Hawaiian Islands through
Wednesday afternoon. The south-southwest swell will continue to
gradually lower from Thursday into next weekend.

Small northwest swells are expected early this week, which will
likely keep surf just above typical summertime flat conditions
along most north facing shores into Wednesday. Strong easterly
trades in the vicinity of, as well as upstream of, the islands
will continue to produce slightly elevated choppy surf along east
facing shores through this evening. As the trades weaken, expect
surf along east facing shores to gradually trend downward from
Tuesday through late in the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Wednesday 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 Wednesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

H Lau/Jelsema/Houston