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Home News Hawaii Area Forecast Hawaii Area Forecast
Hawaii Area Forecast
Area Forecast Discussion for Hawaii
Area Forecast Discussion for Hawaii

Area Forecast Discussion for Hawaii
  • Synopsis
    Trade wind weather will continue across the main Hawaiian islands through the forecast period as high pressure dominates to our north. Clouds and showers will favor windward and mauka areas. Clouds and showers will increase each afternoon and evening across leeward portions of the Big Island. Total rainfall will be light.

  • Discussion
    A 1025 mb high near 30°N 148°W, about 870 miles northeast of the main Hawaiian islands, has an associated ridge extending east through 30°N 140°W and west through 25°N 180°W. The pressure gradient between this ridge and equatorial low pressure is sufficiently steep to support moderate to locally strong easterly trade winds across local waters this morning. Small craft advisories remain in effect for the traditionally windier channels and waters around Maui and the Big Island through Friday afternoon. Showers embedded within the trades continue to see enhancement from a persistent upper trough across the islands. A ragged band of high clouds extending southwest through northeast across the Big Island and adjacent waters marks the eastern flank of this upper trough. Airmass stability varies from slightly unstable near Kauai with cape over 600 j/kg and a negative lifted index value, to stable over the Big Island with cape less than 100 j/kg and a positive lifted index value. The trade inversion from yesterday is higher and weaker this morning, indicating that the upper trough does indeed seem to be having a destabilizing effect. However, limited moisture west of Maui has kept showers isolated and light across the western half of the state. A loose band of low clouds and showers across Maui county and the Big Island is steadily moving west and may increase rainfall slightly across Oahu and Kauai later today. Models show stronger high pressure will build along the ridge northwest of the main islands over the weekend, then push eastward early next week. This will give a slight boost to trade winds across local waters from Sunday onward as the gradient steepens. The upper trough will persist into the middle of next week before filling, likely keeping trade showers active especially at night. In general, expect trade wind weather to continue through the rest of the forecast period with rainfall focusing over windward and mountain areas. The main exception will be the leeward side of the Big Island, where afternoon and early evening clouds and showers are expected each day as onshore flow develops.

  • Aviation
    Update, strong wind shear and deformation accompany the upper trough that extends across the state. Gfs guidance highlights the greatest potential for clear-air turbulence in the area to the northeast of the state. However, recent water vapor imagery shows this area moving westward. Have updated the airmet to include a mention of moderate high-level turbulence across the state, and also brought sigmet oscar for occasional severe turbulence into the windward coastal waters as well. This potential for high-level turbulence may continue through the night. Radar VAD wind profiles and 17Z-18Z ACARS soundings from Honolulu show 20-25 kt of wind below the inversion. We received a couple reports of moderate turbulence yesterday but none so far today. Will keep the airmet going for moderate low-level turbulence. Gfs model cross sections show low-level winds reaching a minimum this afternoon into early Friday, then strengthening again as we head into the weekend. If we do end up dropping the airmet, it will only be for a brief period of time as conditions conducive to turbulence quickly redevelop. Clouds and showers remain focused primarily across windward sections. Conditions will be predominately VFR, with occasional MVFR ceilings and visibilities in showers. An area of moisture east of Maui county will spread westward, enhancing showers and bringing more frequent MVFR conditions tonight into Friday morning. We may eventually need an airmet for mountain obscuration if the low ceilings become more widespread and persistent.

  • Marine
    A small craft advisory remains in effect through Friday afternoon for typically windier areas around Maui and the Big Island. A small swell from the west northwest will peak below advisory levels later today. No other significant swells are expected.

  • HFO Watches/Warnings/Advisories
    Small craft advisory until 6 pm HST Friday for Maalaea Bay, Pailolo channel, Alenuihaha channel, Big Island leeward waters, Big Island southeast waters.

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