Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 220142
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
342 PM HST Mon Jan 21 2019

.SYNOPSIS...
Stable conditions will prevail through Thursday as a surface
ridge remains just north or over the islands. While windward Big
Island will likely experience typical shower activity, most of the
state will be under a stable land and sea breeze pattern,
featuring afternoon clouds and a few showers over island terrain
and partial clearing at night. A front is expected to bring an
increase in showers Friday into Saturday, with cooler conditions
moving in behind it.

&&

.DISCUSSION...
The state remains under a stable and dry south to southeast flow
this afternoon. A passing front, currently about 125 miles north
of state, has kept the subtropical ridge near Kauai and Oahu,
resulting in moderate southerly winds over the these islands and
southeast background flow elsewhere. A ridge aloft is maintaining
stable conditions with an inversion around 5,000 ft, and
precipitable water continues to be below seasonal normal. Aside
from a few showers that passed over Kauai this morning, rainfall
has been scant, and under the dry and stable conditions, afternoon
sea breezes have failed to produce much cloud cover over the
islands.

The stable and somewhat dry weather pattern will persist through
Thursday. As the front stalls and dissipates tonight, the surface
ridge will shift northward slightly. This will allow the gentle to
locally moderate strength background winds to become more
easterly near the Big Island and more southeasterly elsewhere.
This subtle change will not translate into a significant change in
the weather. A land and sea breeze regime will continue to
produce clouds and a few showers over island terrain and interior
sections each afternoon, followed by mostly clear conditions
overnight and in the morning hours. The exception will likely be
over windward Big Island and east Maui, where the more easterly
flow will deliver modest showers. A mid level ridge will remain
overhead, maintaining stable conditions.

A pattern shift is becoming increasingly likely heading into next
weekend. Though minor timing differences remain, the GFS and
ECMWF models have come into better agreement on a frontal passage
for late Friday into Saturday. Although this feature looks to be
weak, expect the front to deliver a period of showers, especially
along windward areas and north facing slopes. Behind the front,
northeasterly winds should usher in a cool air mass with dew
points dropping into the upper 50s.

&&

.AVIATION...
A ridge over the region, with a front to the north, continues to
bring a dry and stable airmass to the islands. The front is
stalling to the north, and not expected to reach the islands.
Generally light winds will prevail, with clearing over the islands
tonight, and clouds developing over interior locations tomorrow.
No AIRMETs in effect.

&&

.MARINE...
Light to moderate southeast winds are expected to hold through
mid-week as a cold front stalls and diminishes north of Kauai and
the ridge remains near the islands. Pockets of fresh, southeast
breezes are likely in the typically windier areas, with moderate
to fresh southerly winds continuing today over the Kauai waters.
Elsewhere, land/sea breezes near the coasts are expected. Another
front may push through the islands toward the end of the week with
gusty northerly winds behind it into the weekend.

Surf along north and west facing shores will gradually rise
through Wednesday as moderate to large, overlapping west-
northwest swells fill in. This will translate to an extended
period of advisory-level surf for north and west facing shores,
late Tuesday into this weekend, with a peak Wednesday through
Thursday near warning levels. This direction (300-320 deg) will
also make it into the leeward Big Island coast from Kona to South
Point late Tuesday through midweek, likely nearing warning levels
there as well. The last reinforcement in the series is expected
Friday through Saturday, which may bring the surf back to around
warning levels Friday night. Surf will gradually lower through
Sunday.

A small increase in surf is expected along 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.

&&

$$

DISCUSSION...Wroe
AVIATION...M Ballard
MARINE...TS


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