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Hawaiian Islands Synoptic Discussion and Guidance

869
FXHW60 PHFO 250623
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
823 PM HST Fri Jan 24 2020

.SYNOPSIS...
A cold front will dissipate over Kauai and Niihau through
Saturday with lingering clouds and showers around both islands.
Trade winds are back and forecast to increase into the moderate
range tonight and last through the weekend. On Sunday, trade winds
will veer towards the southeast direction over the western islands
and the cloudy remnants of the front near Kauai will drift
northward away from the state. A stable light wind pattern will
return from Monday into Tuesday with trade winds transitioning
back to a dry land and sea breeze pattern. Another cold front
approaches the western islands next Friday with wet weather
trends forecast into next weekend.

&&

.DISCUSSION...
The satellite picture this evening shows long low level cloud
bands draped across the western and eastern ends of the state.
Out west a cloud band over Kauai and Niihau is associated with a
dissipating cold front that has stalled over both islands. Back
east another low level cloud band lingers over the Big Island
caused by surface wind convergence. Both cloud bands will increase
cloud cover and produce a slight increase in shower activity for
each island. Otherwise a moderate trade wind flow will favor
isolated to scattered windward and mountain showers for all
islands this weekend.

Monday through Thursday...A large scale low pressure trough
settling in over the Central Pacific basin will weaken the high
pressure ridge north of the islands. Trade winds will transition
to light winds from Monday into Tuesday with local scale land and
sea breezes developing over each island. A fairly stable
atmosphere and background light southeasterly winds will keep
rainfall to a minimum through Thursday.

Friday into next weekend...Long range guidance continues to show
another cold front approaching the islands from the northwest.
Timing and intensity details remain a bit fuzzy this far out in
the forecast time period. However, the best chances for increasing
clouds and showers will develop over the western islands with
these higher precipitation trends reflected in our latest weather
grids. Current American (GFS) and European (ECMWF) suggest a brief
period of showers mainly affecting Kauai County. Due to run to run
model differences on the movement of this frontal band our
confidence in wind and weather solutions remains only fair at
this time. Expect changes to our forecast grids in the extended
range as this part of the forecast will likely evolve over time.

&&

.AVIATION...
A weak front will continue to slide slowly southeast over the
islands and dissipate during the next 24 hours. This feature will
allow light to occasionally moderate trade winds to return across
the region. Thus, isolated to scattered showers are expected to
gradually increase in coverage along the windward coasts and
slopes... especially for Kauai, Maui, and the Big Island.

&&

.MARINE...
A dissipating front will remain nearly stationary in the vicinity
of the Kauai waters tonight. A ridge of high pressure will build
north of the area behind the front, and will bring a brief return
of moderate to locally strong winds tonight through Saturday
night. Another front will approach and stall out to the west of
the islands early next week, diminishing the winds over the
western islands while moderate to locally strong east-
southeasterly winds hang on in the unsheltered areas around Maui
and the Big Island. Another front approaching from the northwest
during the middle and latter part of next week, will diminish
winds further, with light and variable winds prevailing across
most of the island chain.

Seas are expected to rise to SCA levels across most of the marine
area late tonight and Saturday as a new large northwest swell
arrives. Trade winds will also strengthen briefly to SCA levels
across the Alenuihaha Channel Saturday and Saturday night. SCAs
remain in effect for all Hawaiian waters except Maalaea Bay
for the Saturday and Saturday night periods, due to a combination
of winds and seas. Some marine zones will likely hold on to SCA
level seas Sunday into early next week.

Surf will keep pumping along north and west facing shores as a
progressive weather pattern across the northern Pacific keeps a
series of large northwest swells moving through the islands. The
next northwest swell will fill in late tonight and build through
the day Saturday with surf peaking above warning levels late
Saturday into Saturday night. This swell will be on a downward
trend Sunday, but is expected to hold at warning levels during
the day before dropping to advisory levels Sunday night. As this
swell eases early next week, advisory level surf may hold through
Monday before dropping below HSA thresholds Monday night and
Tuesday. Over the Big Island, this swell will likely bring
advisory level surf to exposed west facing shores late Saturday
through Sunday. Another large northwest swell will be possible
during the middle to latter part of next week.

Surf along exposed east facing shores will remain small through the
period due to the lack of persistent trades locally and upstream
across the eastern Pacific.

Surf along south facing shores will remain small through next week.
A couple background south swells expected over the weekend and
again on Tuesday should be enough to keep things from going flat.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning from 6 AM Saturday to 6 PM HST Sunday for
Niihau-Kauai Windward-Kauai Leeward-Waianae Coast-Oahu North
Shore-Oahu Koolau-Molokai-Maui Windward West-Maui Central Valley-
Windward Haleakala.

Small Craft Advisory from 6 AM Saturday to 6 AM HST Sunday for
Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-
Maui County Leeward Waters-Pailolo Channel-Alenuihaha Channel-
Big Island Windward Waters-Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory from midnight tonight to 6 AM HST Sunday
for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward
Waters-Kauai Channel-Oahu Windward Waters.

&&

$$

DISCUSSION...Bohlin
AVIATION...JT
MARINE...Jelsema

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office



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