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Hawaiian Islands Synoptic Discussion and Guidance

778
FXHW60 PHFO 240642 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
842 PM HST Thu Jan 23 2020

.SYNOPSIS...
A stable land and sea breeze pattern will continue through
tomorrow afternoon under a weak subtropical ridge over the
islands. A cold front will move into Kauai and Niihau by Friday
evening spreading clouds and showers over both islands through
Saturday. Trade winds also return during the Friday to Saturday
time period spreading windward and mountain showers to all
islands. Winds shift towards a more southeasterly direction over
the western islands on Monday pushing the remnants of the front
northward away from the state. Land and sea breezes are forecast
in a stable light wind pattern from Tuesday into Friday.

&&

.DISCUSSION...
A stable light wind pattern will produce sunny skies with land
and sea breezes across most of the Hawaiian Islands into Friday.
Drier air aloft will keep low temperatures below normal through
Friday morning. A weak low level disturbance over the Big Island
may slightly increase shower activity tonight along the southeast
slopes.

Friday through Sunday, a cold front will approach Kauai from the
northwest spreading clouds and showers across the Garden Isle by
Friday evening. The forward motion on this front will stall out
with clouds and showers lingering over Kauai and Niihau through
Saturday. Trade winds will bleed out ahead of this cold front on
Friday spreading windward and mauka showers eastward down the
island chain through Saturday morning. Moderate trade winds will
continue to blow across the state through the weekend. Wind
directions across the western islands will veer towards a more
southeasterly direction on Sunday. These winds will push the
remnant cold frontal clouds and showers northward away from the
western islands with improving weather conditions forecast over
Kauai County.

Monday through Friday, a large scale trough anchored over the
Central Pacific will bring another round of stable light winds
with local scale land and sea breezes developing through the work
week. Long range guidance shows another weakening cold front
moving into the western islands on Friday. Additional clouds and
showers are possible over Kauai and Oahu by the end of next week.

&&

.AVIATION...
For the next 24 hours, VFR conditions are expected to
continue across the island chain. Light showers may impact
windward sides of the islands this afternoon due to sea breezes,
but all interior areas will clear out overnight from land breezes.
As high pressure dominates our area, light and variable winds are
expected. Best chances for lower ceilings and rainfall will be
along the windward and southeast slopes of Big Island, which will
hang into the overnight time frame.

No AIRMETS are anticipated at this time.

&&

.MARINE...
Light and variable winds will continue tonight and early Friday,
before shifting around to the north and northeast by late Friday,
then increasing to moderate and fresh levels Friday night.
Locally strong easterly trade winds will then prevail through the
weekend. A new 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.

A Small Craft Advisory (SCA) remains in effect for elevated seas
of 10 feet or greater through 6 AM Friday. Seas are expected to
drop below SCA thresholds Friday, before rising to SCA levels
across a large chunk of the marine area again Friday night and
Saturday as a new large northwest swell arrives and trade winds
strengthen. SCAs will likely be required through the weekend, and
into early next week across portions of the marine area.

Surf will keep pumping along north and west facing shores as a
progressive weather pattern across the northern Pacific keep a
series of large northwest swells moving through the islands. The
current swell is on a steady decline and a High Surf Advisory
remains in effect through 6 AM Friday. Surf heights are expected
to drop down to borderline advisory levels by Friday morning, and
will watch the buoy observations closely and make a decision on a
need to extend the advisory with the morning forecast package.

The downward trend will be short-lived due to another large
northwest swell arriving Friday night into Saturday from a large
area of gale-to storm-force winds that has setup within the
300-320 directional band relative to the islands over the
northwest Pacific. Long-period forerunners should arrive Friday
night with surf likely building to warning levels on Saturday.
This swell will be on a downward trend on Sunday, but may still
hold at warning levels during the day and likely dropping to
advisory levels by Sunday night. As this swell eases into early
next week, advisory-level surf may hold through late Monday before
dropping below on Tuesday. Over the Big Island, this swell will
likely bring advisory level surf to exposed west facing shores
over the weekend. 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 of background south swells expected over the weekend and
next Tuesday should be enough to keep things from going flat.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Olomana-Molokai-Maui Windward West-Maui Central Valley-
Windward Haleakala-Kona-Kohala.

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

&&

$$

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

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



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