Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 221355
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Tue Jan 22 2019

.SYNOPSIS...
Mainly fair weather will prevail through Thursday as a ridge
persists in the island vicinity. Showers carried by the
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 is expected to bring an increase in showers Friday
into Saturday, with cooler condition spreading across the islands
over the weekend.

&&

.DISCUSSION...
A ridge of high pressure will persist in the island vicinity through
the next few days, with mainly southeasterly winds over the area.
An area of low clouds, carried by the winds, have reached the
eastern islands early this morning, bringing some showers to
windward Big Island and Maui. Elsewhere fair weather prevailed, with
minimal low clouds. Early morning Lihue and Hilo soundings both
continued to depict a rather dry airmass, though not as stable
comparing to the past couple of days.

Mainly fair weather is expected through Thursday, with winds light
enough over the islands allowing land and sea breezes to develop
over the islands. A few clouds and showers will develop over the
islands each afternoon, followed by mostly clear conditions
overnight and in the morning hours. The southeast background winds
will also carry some clouds and showers to the area from the east,
reaching the windward areas of the islands at times. Rainfall
amounts will be low as airmass is expected to remain rather dry and
somewhat stable.

The next front is still expected to reach the islands Friday into
Saturday. Interestingly, forecast solutions now exhibited a little
more differences on the timing of this pending system, with ECMWF
a little fastest while GFS is slower. At least both models still
indicated this front advancing down the island chain will be weak,
as the main upper level support with this system stays northeast and
east of the area. There will be enough moisture associated with the
front to bring a period of showers, especially along windward areas
and north facing slopes. Northeasterly winds behind this front
should usher in a cool air mass with dew points dropping into the
upper 50s. Both models do agree upon some troughing will persist
just northeast of the islands over the weekend into early next week,
with northerly winds persisting over the islands.

&&

.AVIATION...
A deep-layer ridge over the islands will promote a mostly dry and
stable atmosphere, with limited cloud and shower coverage. A surface
ridge just N of the islands will support light and variable winds
over Kauai and Oahu, while light to moderate E winds over Maui
county and the Big Island deliver isolated showers to windward
areas. VFR conditions will continue to prevail statewide, and no
AIRMETs are anticipated.

&&

.MARINE...
A stalled front just northwest of Kauai is slated to move north
shortly and dissipate over the far northern offshore waters on
Tuesday. This opens up the opportunity for a ridge over the smaller
islands to move north slowly through Tuesday, resulting in winds
backing to the east and southeast across the main Hawaiian Islands
by Tuesday night. Another front is expected to enter the far
northwest offshore waters Thursday evening. The front is expected to
fall apart as it reaches Kauai late Friday afternoon. Strong and
gusty northeast winds follows immediately behind the front Friday
night through Saturday morning before easing off moderate to locally
strong. A gale low is forecast to form along this front 750 nm
north- northeast of the islands over the weekend, with the trailing
nearly stationary front draped across the far and southern offshore
waters. At the same time, another front is expected to stall and
fall apart just west of our far western offshore waters. This setup
will keep the islands under a moderate to strong north to northeast
wind flow.

The reinforcing west-northwest swell of 300 to 310 degrees, has
reached buoys 51001 and 51101 a little while ago. This swell will be
arrive at our islands later this morning and continue building
through tonight. Advisory level surf is expected to settle in this
evening and peak Wednesday at 10 to 11 feet and 16 seconds. A
reinforcing west- northwest pulse arrives Thursday night, peak early
Friday, followed by a gradually drop through the upcoming weekend.
This translate to an extended period of advisory- level surf to near
warning levels, for north and west facing shores, late Tuesday night
through Wednesday, then again Thursday night through Friday.

From this direction, the swell will reach the Kona coast, from Kona
to South Point Tuesday night, The swell and surf will peak
Wednesday, followed by the second pulse Friday and Friday night,
thus maintaining advisory level surf in the process.

The occurrence of the gale low north-northeast of the islands over
the coming weekend, will lead to slight bump along the exposed north
and east facing shores early next week. Before this happens, a
slight rise is expected along the east facing shores Wednesday into
the second half of the week due to a pocket of fresh to strong winds
upstream of the state. Surf along south facing shores will remain
near the seasonal average through the week with mainly background
short-period southeast trade wind swell energy.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

91.22.84.05


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