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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 220130
Area Forecast Discussion
National Weather Service Honolulu HI
330 PM HST Sat Jan 21 2017
A front moving southeastward across the state this afternoon will
stall near the Big Island tonight through early next week. Very
strong and potentially damaging northeast trade winds will persist
through tonight, with winds expected to ease by early next week.
A cold front across the central islands will move southeast down
the island chain and stall near the Big Island tonight. A strong
surface high moving in behind the front will continue to drive
strong, gusty, and potentially locally damaging northeast trade
winds across the islands and local waters. Winds have already
increased across many areas, with gusts to 40 kt reported at Lihue
and to 55 kt reported on Lanai. A recent ASCAT pass, covering the
western half of the main island chain, showed a broad swath of
solid 30 kt winds around and north of Kauai and Oahu, a swath
expected to spread southward as the front moves by. A High Wind
Warning remains in effect for the entire state (except for Big
Island summits and Haleakala summit) through tonight. There is the
possibility for a Wind Advisory or an extension of the High Wind
Warning for all or portions of the state into the day Sunday.
Models show sustained winds increasing to 40 to 45 kt as they
peak this evening, around and just below the 7800 ft inversion.
This scenario often creates periods of strong, gusty, and locally
damaging winds over and downwind of terrain when the inversion is
based near or just above the mountains. Expect modest showers with
the front to be focused along northern and windward slopes, but
many of these showers will track over to leeward sides of the
islands due to the strong winds. On Sunday, most of the rainfall
will be focused over the windward side of the Big Island, with
drier and more stable air from the surface high moving onto the
western portions of the state.
Winds will decrease and veer out of the east to east-southeast on
Monday and Tuesday as the high to the north is pushed off to the
east. Models hint that some of the dissipated frontal moisture
will drift back up over windward portions of the state during
this period. Otherwise, trade winds and a typical pattern of
windward showers should prevail through much of the work week.
Clouds and showers remain across Kauai and Oahu this afternoon,
and most parts Molokai and Lanai. On Maui and the Big Island, the
clouds and showers are focused over the north through east
portions. The clouds and showers are associated with a front
making its way down the island chain, and are at times bring MVFR
conditions, with isolated pockets of both IFR and LIFR. Expect
little change in the next 6 to 12 hours.
Strong and gusty winds are bring turbulent conditions to many
areas, specifically to the lee of the mountains. Reports a short
time ago of severe turbulence, combined with the forecast of
increasing winds, has prompted the issuance of SIGMET OSCAR over
the smaller islands for the lower levels. This replace the AIRMET
Tango that was out for those areas. AIRMET Tango continues for low
level turbulence to the lee of the mountains on the Big Island.
That AIRMET may be replaced with an expanded SIGMET as the
stronger winds reach down to the Big Island this evening.
AIRMET Tango remains posted for upper level turbulence over the
islands, and for strong surface winds over the islands.
A Gale Warning for very strong northeast trade winds
will continue through tonight for all Hawaiian coastal waters. The
Gale Warning will continue through Sunday afternoon for the windy
areas around Maui County and the Big Island. Advisory-level winds
will very likely continue across all other waters on Sunday when
the winds diminish below gale force.
Very strong trade winds and a short-period north swell will
combine to produce surf above the advisory level on east facing
shores of all islands. A High Surf Advisory remains in effect for
those areas from this afternoon through Sunday afternoon. This
advisory may need to be extended. A new large northwest swell
will likely produce surf well above the advisory threshold along
north and west facing shores of the smaller islands from Tuesday
through Thursday morning. Another large northwest swell is
expected to produce advisory-level surf along north and west
facing shores of the smaller islands starting Friday night.
High Wind Warning until 6 AM HST Sunday for Niihau-Kauai-Oahu-
Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-
Maui Central Valley-Windward Haleakala-Leeward Haleakala-Kona-
South Big Island-Big Island North and East-Kohala-Big Island
High Surf Advisory until 6 PM HST Sunday for Niihau-Kauai
Windward-Oahu Koolau-Olomana-Molokai Windward-Lanai Makai-Maui
Windward West-Windward Haleakala-Big Island North and East.
Gale Warning until 6 PM HST Sunday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Gale Warning until 6 AM HST Sunday for Kauai Northwest Waters-
Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-Oahu
Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County
Windward Waters-Maui County Leeward Waters-Big Island Windward
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office