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Hawaiian Islands Synoptic Discussion and Guidance

371
FXHW60 PHFO 250204
AFDHFO

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

.SYNOPSIS...
Moderate trade winds will build in tonight as front dissipates
over Kauai. Winds will shift southeasterly by Monday as a front
passes by to the north with land and sea breezes prevailing
Tuesday into Thursday. Another cold front may bring wet weather
to the state next weekend.

&&

.DISCUSSION...
Visible satellite across Hawaii shows a dissipating front over Kauai
and a convergence band over the Big Island, where mostly cloudy
skies prevail this afternoon. Between these features on Oahu and
Maui County, mostly sunny to partly cloudy skies prevail. Zonal
flow aloft will keep the atmosphere stable through the next week.
00Z soundings show a strong inversion 7-8 kft high with perceptible
water values just over 1 inch.

Sea breezes set in over the islands this afternoon as the background
winds are light. Trade winds associated with a bubble high building
behind the front will overrun the dissipating front and build to
moderate breezes for all islands by Saturday morning. The trades
will focus clouds and light showers over windward areas Saturday,
but rainfall amounts will be light.

The trade winds will veer east southeast Sunday night and Monday
as another cold front approaches from the northwest. This front
will not directly impact the islands as it will pass well to the
north on Monday. Winds will focus clouds and showers over windward
and southeast slopes of Maui and the Big Island, but localized sea
breezes could set up in some of the blocked leeward areas of Kauai
and Oahu where afternoon clouds will be predominant. Yet another
front will follow this front and will keep the land and sea breeze
pattern flow going for all islands Tuesday through Thursday.
Expect clouds to build up during the daytime and clear out at
night, with no significant rainfall.

Long range guidance shows the cold front moving into the western
islands next Friday, but there are differences between the GFS and
ECMWF. The GFS model brings the front into Kauai and Oahu Friday,
while the ECMWF keeps the boundary just north of Kauai. Expect
these differences in frontal placement to diminish as the forecast
time period grows shorter.

&&

.AVIATION...
Sea breezes with mostly dry and VFR conditions will continue for
most locations into this evening, aside from a weak area of
moisture southeast of the state bringing a few light showers to
eastern portions of the Big Island. As a dissipating cold front
nears Kauai from the northwest this evening and tonight, weak
trade wind flow is expected to return to the central and western
portions of the state, with increasing cloud cover. The bulk of
the clouds and shower activity, though, should remain concentrated
on Kauai, as well as windward locations of the other smaller
islands. No AIRMETS are anticipated through this evening, but may
be needed for mountain obscuration later tonight, especially for
Kauai, as clouds and showers increase with the remainder of the
front.

&&

.MARINE...
A dissipating stationary front will linger around Kauai waters
through tonight. A ridge of high pressure will then 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 into Saturday as a new large northwest swell
arrives. Trade winds will also strengthen briefly to SCA levels
across the Alenuihaha Channel on Saturday. SCAs has been issued
for all Hawaiian waters except the Maalaea Bay for Saturday and
Saturday night due to a combination of winds and seas, with some
areas holding onto SCA level seas 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 threshold 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 north
and west facing shores of Niihau, Kauai, Oahu, Molokai and for
north facing shores of Maui.

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.

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.

&&

$$

DISCUSSION...Foster
AVIATION...TS
MARINE...Kino

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

Current Conditions
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RH		15 %
Wind		SW 7 mph
Road		Open (4x4)