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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 211924
Area Forecast Discussion
National Weather Service Honolulu HI
924 AM HST Fri Jan 21 2022
Winds will remain on the light side today, with trade winds
beginning to filter in later today and tonight. Trade winds will
strengthen this weekend and into next week. Pockets of moisture
will ride in on the trade winds, shifting shower activity back to
the more typical windward and mountain areas.
A cold front northwest of the islands is expected to dissipate
before reaching the islands. Meanwhile, a surface ridge over the
main Hawaiian islands continues to bring light winds to the area,
with daytime sea breezes expected again this afternoon. The ridge
is expected to erode today, allowing for some light trade winds to
filter into the western end of the state by late in the day. A low
pressure system to the northeast will be moving to the southwest
over the next couple of days with little impact on the local
The sea breezes today will allow for some cloud and shower
development over the interior of the islands. As trades begin to
filter back in, look for those areas to see the clouds and showers
once again focus over windward areas. Assuming winds remain on the
light side tonight, there will be some land breezes that will help
to clear out the interior of the islands.
Although the above mentioned front will be dissipating, some
leftover moisture from the front could reach the islands
(particularly Kauai and Oahu) beginning tonight. Northeasterly trade
winds are expected to increase Saturday with the high pressure
system setting up north of the island, and the low pressure stays
to the east of the islands. The leftover frontal moisture is
expected to peter out Sunday. Trades are expected to pick up
further during the first part of the new week, and moisture from
the low to the east will be picked up in the trade wind flow.
An upper level system will brush the Big Island Sunday increasing
winds over the Big Island summits.
A ridge of high pressure will remain over the islands through the
TAF period, while a cold front weakens as it approaches from the
northwest. Weakly organized sfc winds continuing into this
afternoon, will allow for some sea breeze circulations mainly over
the sheltered leeward side of the islands, while an overall
transition to easterly trades begins today and continues through
Saturday. Showers remain limited across TAF locations today, with
only an isolated shower possible along sea breeze and trade wind
developments. Shower chances increase in areal coverage Saturday
along favored windward slopes as trade winds settle in.
No AIRMETs are currently in effect, and none are anticipated.
One more day of light winds should be expected today before trades
winds start to make their return tonight and this weekend. Locally
strong winds could return to the typically windier waters around
the Big Island and Maui County by tonight. The Small Craft
Advisory (SCA) may need to be expanded tonight or tomorrow for
these areas due to winds.
The current SCA configuration covers the coastal waters around
Kauai and north of Oahu for the building west-northwest swell and
expected combined seas above 10 feet. For the building west-
northwest swell, we just started seeing the long period energy
arrive at NDBC Buoys 51001 and 51101, a few hours behind
guidance. This swell should peak near the islands late tonight
into Saturday at extra-large levels. A High Surf Warning (HSW) is
posted for the exposed north and west facing shores of the
smaller islands. As the swell builds today, it is also expected
that the HSW will be expanded with afternoon package to cover the
west shores of the Big Island. The SCA will likely be expanded
down the island chain as the combine seas build as well.
Although a downward trend is expected through the second half of
the weekend, another long-period, west-northwest pulse arriving by
Sunday night will support a return of advisory-level (if it dips
below Sunday) surf Monday. Heights are expected to fall below
advisory levels for north and west facing shores Tuesday through
the second half of next week.
Surf along east facing shores may trend up over the weekend in
response to a tight gradient that has setup between low pressure
centered more than 1000 miles east of Hilo and high pressure to its
north. Recent ASCAT data showed a packet of strong- to gale-force
winds focused at the state north of the low. Guidance has this
easterly swell arriving by Saturday night, then lingering into early
next week before easing. Current guidance is showing the surf
staying just below the Advisory levels for east facing shores.
High Surf Warning until 6 PM HST Saturday for north and west
facing shores of Niihau-Kauai-Oahu-Molokai. And north facing
shores of Maui.
Small Craft Advisory until 6 PM HST Saturday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office