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Hawaiian Islands Synoptic Discussion and Guidance

865
FXHW60 PHFO 201940
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
940 AM HST Thu Jan 20 2022

.SYNOPSIS...
A weakening ridge over the state will produce one more day of
light and variable winds. Expect afternoon clouds and a few spotty
showers over island interior sections, while showers will be more
widespread on the Big Island and Maui, especially on southeast
slopes. High pressure passing north of the state will bring a
return of light trade winds on Friday. Winds will increase to
moderate strength trade this weekend and push an area moisture
over windward slopes, followed by brief drying late Sunday into
Monday. Another increase in trad wind showers is possible late
Monday and Tuesday.

&&

.DISCUSSION...
A surface ridge will remain over the state and produce light and
variable winds for one last day. The ridge currently stretches
over Kauai and is producing east to southeast winds around the Big
Island that shift out of the south over the Garden Isle. An area
of diffuse low level moisture is being pushed onto southeast
slopes of the Big Island and Maui this morning. Expect showers to
persist along these slopes today, while afternoon sea breezes
produce more extensive afternoon clouds and showers along leeward
Big Island and Maui as compared to the last several days. Ridging
aloft will maintain stable conditions and inhibit heavy shower
development. For Kauai, Oahu, and Molokai, afternoon sea breezes
will lead to scant shower activity. The weakening surface ridge
will hang on tonight, leading to overnight land breezes and
clearing over most areas.

Friday will be a transition day, with trades staging a comeback.
Surface high pressure will build north of the state while a cold
front stalls and begins to dissipate within 100 miles north of
Kauai. Initially, conditions will be rather dry, but moisture from
the dissipating front may be pushed into windward Kauai and Oahu
Friday night.

Trade winds will increase to moderate strength on Saturday as a
surface ridge holds north of the state, and trades will likely
shift out of the northeast on Sunday as a weak surface approaches
from the east. The moisture from the dissipated front should clear
out and lead to a decrease in showers Sunday afternoon. In
addition, an upper level low dropping southward to the east of the
state will produce increased north winds on the high summits of
the Big Island.

Expect trade winds to remain in place through next week, possibly
becoming breezy and gusty by Wednesday. The above mentioned
surface low will fall apart, but its remaining moisture will fuel
windward rainfall for parts of the state late Monday and Tuesday,
especially for the Big Island and Maui.

&&

.AVIATION...
With a surface ridge over the western end of the state, winds
will remain light to moderate. Sea breezes will develop during the
day over many areas, with land breezes taking hold in the
overnight hours. Showers will mainly form over mauka and interior
sections during the afternoon and early evening, with clearing as
the nighttime progresses. Also, a weak east wind regime over the
Big Island this morning is bringing showers into the eastern and
southeastern parts of the isle.

A weak trade wind flow will likely return statewide Friday as the
surface ridge moves north of the islands.

No AIRMETs are in effect, and none are anticipated through
tonight.

&&

.MARINE...
A surface ridge over the area will continue to support light to
locally moderate winds into tonight, favoring an E to SE
direction near the Big Island, and SE to S near Kauai. A weakening
front moving toward the area will cause the ridge to move S and
weaken and light and variable winds will prevail from tonight into
Friday. A high pressure cell passing N of the area will then
support moderate to locally fresh NE winds from Friday afternoon
into early next week, potentially reaching Small Craft Advisory
(SCA) levels over the typically windy waters around Maui County
and the Big Island. The passing high will also push fragments of
the front over the area, leading to an increase in showers, mainly
over windward waters Friday and Saturday.

The current NW swell is on the slow decline today as available
buoy observations indicate the swell is diminishing in height and
period. This will only be a temporary lull however, as a powerful
long-period WNW swell is expected to build Friday, peak Friday
night/Saturday, then gradually diminish through Sunday. Surf
heights are expected to reach or exceed High Surf Warning (HSW)
criteria during the peak of the swell for exposed N and W facing
shores, including the W facing shores of the Big Island. After
dropping below HSW levels, continued reinforcements from the WNW
may require a High Surf Advisory (HSA) through early next week.
The weekend's large WNW will bring combined seas over 10 feet,
requiring a SCA for seas in most zones. Additionally, a small to
moderate ENE swell is possible over the weekend, generated by a
gale low E of the islands. There will be also a slight increase
in short period choppy surf for east facing shores as moderate to
fresh trade winds return.

&&

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

&&

$$

DISCUSSION...Wroe
AVIATION...Kinel
MARINE...Burke/Shigesato

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



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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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