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Hawaiian Islands Synoptic Discussion and Guidance

805
FXHW60 PHFO 271359
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
359 AM HST Mon Jan 27 2020

.SYNOPSIS...
Moderate trade winds will continue through the morning, with a
few light showers favoring windward areas. Winds will shift to
southeasterly this afternoon through Thursday as a series of
fronts approach from the northwest, with land and sea breezes
developing across the smaller islands. Rather dry conditions will
prevail through much of the work week. A strong front will move
into the islands Friday through the weekend, potentially bringing
wet and unsettled weather.

&&

.DISCUSSION...
Currently at the surface, a 1029 mb high is centered well east-
northeast of the state, with the ridge axis extending westward to
a location around 225 miles north of Kauai. The resulting
gradient is producing moderate trade winds across the island
chain early this morning, although some of the more sheltered
leeward areas have cooled enough to allow for land breeze
development. Infrared satellite imagery shows clear to partly
cloudy skies in place across most of the state, with a few pockets
of enhanced cloud cover over windward locales. Meanwhile, radar
imagery shows a few light showers moving into windward areas, and
dry conditions in leeward locales. Main short term concerns
revolve around rain chances and wind trends over the next few
days.

The surface ridge will remain north of the island chain through
Tuesday, before sliding southward and over the state Wednesday and
Thursday. The first in a series of cold fronts will approach from
the northwest during the first half of the work week, with a
second and stronger cold front moving into the western islands
Friday, before stalling over the weekend. Moderate trade winds
are expected to prevail this morning. Boundary layer winds will
then begin to shift around to the southeast this afternoon, and
will hold in this general direction through much of the work week.
This will keep moderate east to southeast winds in place across
the eastern end of the state, while most of the smaller islands
see light and variable winds featuring daytime sea breezes and
overnight land breezes. Trade winds could return from northwest to
southeast down the island chain late Friday into the weekend as a
strong high builds in behind the second front.

Rather dry weather will prevail across the islands through much
of the work week, as precipitable water values hold generally at
or below 1 inch and deep layer ridging persists over the region. A
few light showers will be confined primarily to windward areas
this morning. This afternoon we should begin to see a few cloud
buildups and interior showers develop as sea breezes become more
common, but shower coverage is expected to remain sparse. This
pattern featuring a few cloud buildups and showers over the island
interiors will then hold in place through Thursday, although some
windward showers will continue across the eastern islands in
areas favored under east-southeast to southeast boundary layer
flow. We will likely begin to see some jet cirrus spread across
the islands on Wednesday as well. It appears the high clouds will
be thin initially, then thicken up a bit Wednesday night into the
weekend. More unsettled weather will be possible beginning
Thursday night or Friday, and holding into the weekend as the
stronger of the two fronts enters the islands. Although the models
differ on the specifics, some wet weather appears likely for at
least portions of the state, particularly windward locales Friday
through Sunday.

&&

.AVIATION...
A surface ridge nearing the state will allow the winds to weaken
even more as we press through the day. The winds will be weak
enough in most areas to have a daytime sea breeze/nighttime land
breeze scenario. Moisture is very limited and the atmosphere is
stable so although there may be a few mauka showers, we are not
expecting any consistent mountain obscurations or visibility
problems through this forecast period. Most of the Hawaii will
see VFR conditions.

There are no AIRMETs currently in effect or expected.

&&

.MARINE...
A ridge of high pressure north of the area will maintain moderate
to locally strong trade winds across most coastal waters through
today. Starting tonight, winds are expected to decrease and veer
to the southeast as a front passes north of the state causing the
ridge to shift over the Hawaiian waters. Winds are expected to be
light and variable across Kauai and Oahu and moderate to locally
fresh out of the east to southeast direction over Maui County and
the Big Island through most of the week. A shift in weather
pattern is possible Thursday into Friday as a front approaches
from the northwest.

The current northwest swell continues to gradually decrease and
will remain at advisory levels across exposed north and west
facing shores of smaller islands through today. Along west facing
shores of the Big Island, surf has dropped below advisory levels.

The Small Craft Advisory (SCA) has been scaled back, but remains
in effect for areas exposed to the northwest swell and for some of
the typical windy areas around Maui County and the Big Island
through today. The SCA will likely be scaled back again later
today as the northwest swell continues to decline and winds also
begin to decrease.

Surf will remain elevated along north and west facing shores as a
progressive weather pattern across the northern Pacific keeps a
series of moderate to large northwest swells moving through the
islands, at least through the middle to latter part of the week.
The next northwest swell is expected to arrive Tuesday night and
peak at solid advisory levels sometime Wednesday. A larger
northwest to north-northwest swell will be possible towards the
end of the week and could bring warning level surf to exposed
north and west facing shores by Friday night. This swell has yet
to develop and appears to have large differences in wave heights
compared to the European model, thus confidence in surf heights
remain low for the end of the week swell. Stay tuned for updates.

Surf along exposed east facing shores will remain rather small
through the period due to the lack of persistent trades locally
and upstream across the eastern Pacific. An increase in surf is
possible over the weekend as trades possibly return.

Surf along south facing shores will remain small through the
week. However, background south swells should be sufficient to
keep things from going flat.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening 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 until 6 PM HST this evening for Kauai
Northwest Waters-Kauai Windward Waters-Oahu Windward Waters-
Kaiwi Channel-Maui County Windward Waters-Pailolo Channel-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Chevalier
MARINE...Kino

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

Current Conditions
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RH		7 %
Wind		NE 28 mph
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