Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 201919
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
919 AM HST Mon Jan 20 2020

.SYNOPSIS...
Moderate to locally breezy trade winds will continue today, then
diminish Tuesday through Friday as the low level winds shift
around to the southeast. Typical trade wind showers will prevail
today and tonight, with a mostly dry land and sea breeze pattern
then expected through the remainder of the work week, with only a
few clouds and showers developing over interior and mountain
areas each afternoon. A front is expected to stall and weaken
near Kauai Friday night, with trades then returning over the
weekend.

&&

.DISCUSSION...
Currently at the surface, a 1024 mb high centered around 450 miles
northeast of Honolulu is driving moderate to locally breezy trade
winds across the island chain this morning. Meanwhile, the first
in a series of fronts is located around 1300 miles west-northwest
of Kauai, or just to the west of Midway Atoll. Infrared satellite
imagery shows partly to mostly cloudy skies, with cloud cover most
prevalent in windward areas. Radar imagery shows scattered showers
moving into windward areas, with a few of these showers making
the trip over into leeward locales. Main short term concern
revolves around the diminishing trade winds.

High pressure northeast of the state will shift eastward over the
next couple of days as a front approaches from the northwest and
passes by several hundred miles north of the island chain.
Moderate to locally breezy trade winds will hold today, then
begin to diminish tonight and early Tuesday, with land and sea
breezes then expected to prevail Tuesday afternoon through
Friday. A new front will be approaching the islands from the
northwest late in the work week, and is expected to stall near
Kauai Friday night. High pressure will build in behind the front
to the north of the islands over the weekend, allowing the trade
winds to return. The next front approaching the area from the
northwest Sunday night into early next week, could disrupt the
trade winds once again.

Typical trade wind showers, favoring windward and mauka areas
along with the occasional leeward spillover, will continue
through the morning hours. We should see shower coverage diminish
considerably by late morning/early afternoon as a drier airmass
builds in. Trade showers will continue tonight into Tuesday
morning, but the shower coverage should be much less than what
occurred earlier this morning. A land/sea breeze pattern is then
expected to take hold Tuesday afternoon through Friday. This will
bring a rather dry period of weather to the state, with a few
showers popping up each afternoon over the interior and mountain
areas, with mainly rain free weather at night. An increase in
showers will be possible Friday night and Saturday as a front
stalls out near Kauai and the trade winds begin to return. Shower
coverage will likely be the highest across Kauai, particularly
windward areas, although some increase in windward showers will
be possible across windward sections of the other islands as
well. Fairly typical trade wind showers should then continue
through the remainder of the weekend, with a land/sea breeze
pattern potentially setting up again early next week.

&&

.AVIATION...
Showers continue to impact both windward and leeward areas of the
island chain this morning. These showers will allow for some brief
periods of MVFR conditions, but VFR will prevail overall. Expecting
clouds and showers to become more scattered and confined to the
windward slopes and coasts as the day goes on.

Trades will be on the decline later today as they shift around to
a more east-southeasterly direction for Tuesday. This decrease
will allow AIRMET Tango for tempo moderate low level turbulence
below 7,000 feet to be cancelled by tonight.

&&

.MARINE...
High pressure is currently centered several hundred miles north-
northeast of the state resulting is breezy trade winds across the
area. A Small Craft Advisory (SCA) is currently posted for all
Hawaiian Coastal Waters due to a combination of strong trade winds
and rough seas. The high will move off to a position far to the
east-northeast of the area over the next couple of days with trade
winds becoming lighter. By midweek, a front will be approaching
the area from the northwest. Winds will become south to southeast
and remain on the lighter side as the front stalls northwest of
the area. However, large northwest swells will likely cause seas
to reach SCA levels over exposed waters at times.

A High Surf Advisory is currently posted for waters exposed to a
moderate size north-northwest swell. Data from the nearshore buoys
indicate the swell has likely peaked and will lower gradually
tonight through Tuesday night.

A rather active period for high surf is expected this week as
strong low pressure systems pass across the North Pacific over the
next several days. These low pressure systems will be rather
robust swell producers. A large and very long period northwest
swell is expected to begin arriving Tuesday night. This swell is
expected to build on Wednesday, peak Wednesday night, then lower
gradually Thursday through Friday. Latest guidance indicates that
surf heights will likely reach High Surf Warning levels along most
north and west facing shores during the peak of this swell.
Another large northwest swell is expected to build late Friday and
Friday night, peak on Saturday, then lower gradually Saturday
night through Sunday. Warning level surf is once again expected
during the peak of this swell.

Only small background south swells are expected through the week
and on into the weekend. With the expected drop off in trade winds
over the next few days, short period choppy surf will diminish
along east facing shorelines. However some south and east facing
shores may see some localized higher surf this week from the
large northwest swells refracting around islands and reefs.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Olomana-Molokai-Maui Windward West-Maui Central Valley-
Windward Haleakala.

Small Craft Advisory until 6 PM HST this evening for all
Hawaiian waters-

&&

$$

DISCUSSION...Jelsema
AVIATION...Dye
MARINE...Burke


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