FORECAST DISCUSSION

Synopsis

21 Nov 2017 01:46:00 GMT: A surface low about 1000 miles northeast of the islands will move away to the northeast. A surface high far north of the area will move southeast through Thanksgiving Day, then dissipate. A strong new surface high will build far northwest of the islands on Wednesday, then move southeast through early next week. A trough aloft will remain over the area.

Discussion

21 Nov 2017 01:46:00 GMT: The pressure gradient between a surface high far north of the area and a low to the northeast is producing gentle to fresh north winds. Satellite water-vapor imagery shows a trough aloft extending north from over the islands. Despite the trough, the atmosphere remains dry and stable. Balloon soundings at 200 PM showed strong temperature inversions near 6900 feet at Lihue and 5000 feet at Hilo. The north winds are carrying isolated showers over north sections of the islands but rainfall has been quite light. Rainfall should generally remain light, but the north winds could boost rainfall over the northeast slopes of the Big Island. The trough aloft continues to produce strong west winds over the summits of Mauna Kea and Mauna Loa on the Big Island of Hawaii. A Wind Advisory is in effect for the summits. The winds are expected to gradually subside as the trough weakens. Over the next couple of days, the surface low northeast of the area will move northeast and weaken while the surface high moves southeast and weakens. Winds over the islands will shift out of the northeast by Tuesday. The global models show a low-cloud band moving over Kauai County from the northwest Tuesday afternoon, moving over Oahu and Maui County Tuesday night, and pushing down over the Big Island by Wednesday evening. This cloud band will bring an increase in clouds and showers to windward areas. Starting Wednesday night, a strong new surface high far northwest of the islands will start moving southeast. The northeast trade winds over the islands will strengthen and become breezy. Wind speeds will likely decrease again starting Saturday, but trade winds will likely persist through at least early next week.

Aviation

21 Nov 2017 01:46:00 GMT: Cool northerly winds will push a band of clouds and showers over the islands tonight. This band is currently about 50 nm north of the island chain this afternoon. VFR conditions prevail at this time, but an AIRMET for tempo mountain obscurations may be issued later tonight as the band of clouds approaches. The highest coverage for shower activity will occur over mountain areas and the northern slopes of all islands.

HFO Watches/Warnings/Advisories

21 Nov 2017 01:46:00 GMT: High Surf Advisory until noon Tuesday for north facing shores of Niihau, Kauai, Oahu, Molokai, Maui and the Big Island of Hawaii. High Wind Advisory until noon Tuesday for the summits of Mauna Kea and Mauna Loa on the Big Island. Small Craft Advisory until noon Tuesday for all coastal waters except Maalaea Bay and waters south and west of the Big Island.

Footer

21 Nov 2017 01:46:00 GMT: DISCUSSION...Donaldson Aviation...Foster Marine...Kodama

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