Surf n Sea 12 Day Count down

FORECAST DISCUSSION

Synopsis

14 Dec 2018 20:19:00 GMT: Breezy trade winds will persist through tonight due to surface high pressure north of the islands. The winds will gradually diminish from this weekend into early next week as this high moves slowly south and weakens. A stable weather pattern with brief windward and mauka showers will prevail through Monday. Expect dry conditions across most leeward areas. A front is expected to move down the island chain from late Tuesday through Wednesday, bringing an increase in showers and breezy northeasterly trade winds.

Discussion

14 Dec 2018 20:19:00 GMT: A surface high is centered several hundred miles north of the state. This places the islands in a moderate to locally breezy trade wind environment. The airmass in the island vicinity is rather dry and stable as indicated by the 12Z soundings from both Lihue and Hilo. Satellite imagery shows stable low clouds moving westward in the trades but radar imagery shows very little in the way of precipitation falling from them. These conditions will continue through the day today. A Wind Advisory has been posted through tonight for the Big Island summits with sustained wind speeds exceeding 45 MPH being reported. Winds are expected to diminish later tonight and Saturday. The global models are in good agreement for the upcoming weather scenario. A cold front will be passing by far north of the state this weekend. It will nudge the surface high a bit to the south resulting in a deceleration of the trades from present levels. The airmass is expected to remain rather dry and stable so only a few light showers are expected over windward and mauka areas with most leeward locations remaining dry through the weekend. By Monday, another cold front will be approaching the area from the northwest. This front will push the surface high off to the northeast of the area with trade winds dropping off to lighter levels. Local land and sea breezes may develop in some areas under this lighter wind regime. By the time the front reaches the island vicinity, it is expected to be rather shallow and weak with the best upper level dynamics remaining far north of the state. Current timing shows the front reaching Kauai late Tuesday, then spread down the island chain Tuesday night through Wednesday night. Breezy north to northeast winds will accompany the frontal passage. This will cause the greatest increase in shower activity over north and northeast facing slopes and well as areas immediately downwind of terrain. With the front being rather shallow, heavy rainfall is not expected. A drier trade wind weather pattern is expected to follow in the fronts wake.

Aviation

14 Dec 2018 20:19:00 GMT: High pressure centered N of the islands will move S weaken over the next 24 hours, allowing strong and gusty trade winds to gradually ease. The interaction between the ENE trade winds, the island terrain, and a subsidence inversion based around 6000 feet will continue to produce low-level turbulence to the S and W of all islands. In fact, latest satellite imagery shows low- level wave clouds extending up to 100 miles to the SW of the islands. AIRMET Tango for low-level turbulence will remain posted into at least Saturday. The trade winds will deliver scattered, primarily stable, low clouds that will focus over windward slopes and coasts. Brief periods of MVFR VIS/CIG in -SHRA, are expected, but the strongly-capped and relatively dry atmosphere will keep rainfall very light. VFR conditions will prevail at all TAF sites through tonight.

Marine

14 Dec 2018 20:19:00 GMT: Strong trade winds will continue today with high pressure passing north of the area. A combination of winds and seas will maintain Small Craft Advisory (SCA) conditions today across all coastal waters. The current northwest swell is on the decline and expected to remain below High Surf Advisory (HSA) levels through Saturday. As the swell subsides, seas will drop below SCA levels. Trade winds are expected to weaken some tonight and Saturday. By tonight, some of the coastal waters will drop out of the SCA, and additional areas will drop below criteria tomorrow. A large northwest swell will build late Saturday, peaking Sunday at warning levels, and start to subside Monday. An even larger northwest swell will build late Monday, once again peaking at warning levels. These swells will once again bring seas in excess of 10 feet to the waters exposed to these swells. At the same time, moderate to locally breezy trade winds will continue to bring SCA level winds to the typically windier areas near Maui County and the Big Island. The result will be SCA conditions for most, if not all, the coastal waters for the first half of the week. The HSA in effect today for east facing shores of Kauai, Oahu, Molokai, Maui, and the Big Island is due to short-period, rough surf produced by the strong trades. Surf should lower below advisory levels by this evening as the trades ease. See the latest Oahu Surf Discussion (SRDHFO) for additional details on surf and swell.

HFO Watches/Warnings/Advisories

14 Dec 2018 20:19:00 GMT: High Surf Advisory until 6 PM HST this evening for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, South Big Island, Big Island North and East. Wind Advisory until 6 AM HST Saturday for Big Island Summits. Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters,

Footer

14 Dec 2018 20:19:00 GMT: DISCUSSION...Burke AVIATION...TS MARINE...M Ballard

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