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Hawaiian Islands Synoptic Discussion and Guidance

979
FXHW60 PHFO 230155
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
355 PM HST Tue Jan 22 2019

.SYNOPSIS...
Stable conditions will prevail through Thursday as a ridge
remains just north or over the islands. While windward Big Island
and east Maui 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 will move down the
island chain Friday into Saturday, bringing a period of rainfall
and ushering in cool northeast winds for the weekend.

&&

.DISCUSSION...
The state has been under a stable east to southeast flow today.
A surface ridge sitting about 75 miles north of Kauai is driving
a moderate to fresh easterly trade wind flow around the Big Island
and a weaker southeast background flow near the Garden Isle. A mid
level ridge overhead is maintaining stable conditions, and
precipitable water remains near to below January normal. Under
these stable and somewhat dry conditions, afternoon sea breezes
have produced clouds over island terrain, but little rain has
fallen.

Land breezes will develop from Kauai to much of Maui this evening,
while easterly trades persist around the Big Island and east Maui.
An area of slightly elevated low level moisture should ride in on
the trades tonight and deliver modest showers for windward Big
Island and east Maui. Expect rather dry conditions and a decrease
in cloud cover from Kauai to much of Maui as land breezes develop
during the evening.

The stable and somewhat dry weather pattern will persist through
Thursday. Over most areas, a land and sea breeze regime will
continue to produce clouds and some showers each afternoon,
followed by mostly clear conditions overnight and in the morning
hours. Persistent easterly trade wind flow around windward Big
Island and east Maui will continue to bring modest showers. A mid
level ridge will remain overhead, maintaining stable conditions.

A front will move down the island chain Friday into Saturday. The
GFS and ECMWF models are in fairly good agreement, showing clouds
and showers along the front reaching Kauai Friday afternoon then
moving down to the Big Island late Friday night or Saturday
morning. Expect rainfall to favor north facing terrain and
windward slopes, though all areas should pick up shower activity.
The greatest upper level support will be off to the northeast of
the state, lowering the probability of heavy rainfall along the
front.

Breezy northeast 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, with a few showers
blowing across leeward portions of the smaller islands. This cool
winter weather should hold through Monday.

&&

.AVIATION...
VFR conditions will prevail. A surface ridge will remain near
Kauai through Thursday. The ridge will produce gentle variable
winds over Kauai and Oahu and moderate E winds over Maui county
and the Big Island. The E winds will carry scattered showers over
the east side of the Big Island and possibly Maui, mainly during
the night and early morning hours. Sea breezes will produce
afternoon clouds over interior areas of Oahu and Kauai. The
atmosphere over the area will remain dry and stable through
Thursday, so clouds and showers will be limited.

A trough aloft is creating enough shear to product moderate
turbulence aloft. An AIRMET is in effect for this turbulence. The
turbulence will subside as the trough shifts east.

&&

.MARINE...
A ridge will remain just north of Kauai through Thursday putting
the island chain in a light to moderate east southeast wind flow.
A weak cold front will move through the islands Friday and
Saturday, with fresh to strong northeast winds filling in behind
on Saturday.

A northwest swell will build tonight, peaking at around 10 feet,
16 seconds on Wednesday and Wednesday night. Surf along north and
west facing shores will reach advisory levels with this swell, as
well as on the Kona coast of the Big Island. A High Surf Advisory
goes into effect at midnight tonight through Thursday for the
affected shores of the smaller islands, and then at 6 am HST
Wednesday for the Kona coast. A reinforcing northwest swell of
similar size will arrive Thursday night, peak early Friday, then
drop off this weekend. A Small Craft Advisory (for seas) also
goes into effect at midnight tonight for coastal waters exposed to
both northwest swells. A small east swell expected Wednesday into
Thursday due to a pocket of fresh to strong winds upstream of the
state. Surf will remain small across the south facing shores this
week.

The occurrence of the gale low north-northeast of the islands
this weekend will lead to slight bump along the exposed north and
east facing shores early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory from midnight tonight to 6 PM HST Thursday
for north and west facing shores of Niihau, Kauai, Oahu, and
Molokai and for north facing shores of Maui.

High Surf Advisory from 6 AM Wednesday to 6 PM HST Thursday for
west facing shores of the Big Island.

Small Craft Advisory from midnight tonight to 6 PM HST Thursday
for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward
Waters-Kauai Channel-Oahu Windward Waters-Maui County Windward
Waters-Big Island Windward Waters.

&&

$$

DISCUSSION...Wroe
AVIATION...Donaldson
MARINE...Foster

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



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