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WindNNW 14 mph
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Hawaiian Islands Synoptic Discussion and Guidance

418
FXHW60 PHFO 231402 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
400 AM HST Wed Jan 23 2019

.SYNOPSIS...
Fair weather will prevail through Thursday as a ridge remains in the
island vicinity. Showers carried by the east to southeasterly wind
flow will reach the windward areas at times. Afternoon clouds and a
few showers will develop over the islands under daytime sea breezes,
with partial clearing at night under land breezes. A front will move
down the island chain Friday into Saturday, bringing a period of
rainfall and ushering in cool northeast winds for the weekend.

&&

.DISCUSSION...
Fair weather prevails across the state early this morning, with only
a few showers reaching windward Big Island. A surface high pressure
ridge remains north enough to allow easterly trade winds over the
eastern islands, then becoming weaker southeast winds over the
western islands. An upper level ridge overhead is maintaining
marginally stable atmospheric conditions, with a rather dry airmass
prevailing across the area. Early morning Lihue and Hilo soundings
are quite similar to Tuesday afternoon's, though there is a more
pronounced trade wind inversion signature on the Hilo sounding
profile, with low level moisture extending to about 7 thousand feet.

The land and sea breeze weather regime that has been around the area
for a while will persist through Thursday. Clouds and some showers
will develop during the afternoon over the islands, followed by
mostly clear conditions overnight through the early morning hours.
Easterly trade winds will bring some clouds and showers mainly to
windward Big Island and east Maui. Rainfall amounts will be limited.

Change in the weather is expected by Friday, as a front will move
down the island chain Friday into Saturday. Latest forecast
solutions are still in fairly good agreement, showing clouds and
showers along the front reaching Kauai Friday afternoon, then
advancing down the island chain and reaching the Big Island late
Friday night or Saturday morning. Expect rainfall to favor north
facing terrain and windward slopes, though rest of the areas may see
some precipitation as well. Much of the upper level support for this
frontal system will stay to the northeast of the state, hence the
probability of heavy rainfall along the frontal band will be low.

Breezy northerly winds will likely develop behind the front,
ushering in a cool airmass with dew points in the mid to upper
50s. Showers will favor windward slopes, and even reaching the lee
portions of the smaller islands. This cool winter weather should
hold through Monday.

&&

.AVIATION...
VFR conditions will prevail as a surface ridge of high pressure
remains just north of the islands in a stable atmosphere. Light
winds will allow land and sea breezes to develop and modify wind
directions with some interior and mountain clouds over each island
during the afternoons.

No AIRMETs in effect and none expected.

&&

.MARINE...
A ridge will remain just north of Kauai through Thursday putting the
island chain in a light to locally moderate east to southeast wind
flow. A cold front will move through the islands Friday and
Saturday, ushering a brief period of moderate to locally strong
northeast winds.

The west-northwest swell came alive in the past couple of hours as
buoy 51001 topped 13.8 feet, 16 to 17 seconds. Buoy 51101 was
slightly smaller at 11 feet. With this data, the swell is up to
three feet above WAVEWATCH III guidance. We also bumped up the High
Surf Advisory to a warning for the north and west shores of Kauai
and Niihau. With this swell coming in at 300 to 310 degrees, the
swell will be blocked downwind, thus slightly smaller surf for the
islands east of Kauai and Niihau. But it will still be advisory for
these island's west and or north shores. The warning and advisory
are in effect through 6 pm HST Thursday. Advisory level surf will
also reach the leeward shores of the Big Island later today, lasting
through Thursday.

Another west-northwest swell, but slightly smaller in size, is due
in Thursday night, peak Friday, followed by a slow but gradual
decline through the weekend. This swell, which tend favor advisory
level surf, will prolong the High Surf Advisory through Saturday.

No new northwest swell is expected over the weekend, but a moderate
west-northwest swell, from 300 to 310 degrees, reaches our north and
west facing shores Sunday night. It will max out at 7 feet and 16
seconds on Monday. This translate to surf heights near advisory
level of 15 feet along the north facing shores.

A Small Craft Advisory (SCA) for seas, is in effect through Thursday
afternoon for near-shore waters exposed to both northwest swells.
The SCA, which is set to expire at 6 pm HST Thursday, could be
extended through at least Friday. We will see how big the next
northwest is before making this determination.

A slightly elevated east swell, generated by a pocket of moderate to
strong trade winds upwind of the islands several days ago, has
arrived. The swell is expected to peak today and hold through
tonight, followed by a slow decline through Friday. The surf may
bump up to near advisory level for east facing shores at its
highest. Some south facing shores, exposed to this swell, may see
bigger surf as well. Otherwise, surf along south facing shores will
be small throughout the period.

WAVEWATCH III is suggesting a small north-northeast swell late in
the weekend, followed by a building north swell Monday, peaking
Tuesday night at 6 feet 12 seconds. This may bring advisory to the
east facing shores with a northern exposure. The source of this
swell is from a forecast gale low some 950 nm north of the islands
over the upcoming weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM HST Thursday for north and west facing
shores of Kauai and Niihau.

High Surf Advisory until 6 PM HST Thursday for north and west facing
shores of Oahu and Molokai, north facing shores of Maui and west
facing showers of the Big Island.

Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Alenuihaha Channel-Big Island Windward Waters.

&&

$$

DISCUSSION...Hui
AVIATION...Bohlin
MARINE...Lau

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