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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
    A strong ridge north of the area will keep trade winds locally breezy. A slight weakening is possible on Friday and Saturday as a front passes north of the state, then a new high will build in to our north early next week. The trades will focus showers primarily over windward slopes. Some showers will spread leeward over the smaller islands, mainly nights and mornings. Afternoon showers are expected over the lee slopes of the Big Island.

  • Discussion
    Water vapor imagery shows an upper level ridge over/northeast of the state. At the surface, high pressure is located northeast of the state, with a ridge passing several hundred miles to our north. 00Z soundings from Lihue and Hilo show inversions of 7-9kft. Precipitable waters are 1.0 and 1.2 inches respectively, which is near average for April. Early afternoon mimic total precipitable water imagery shows a pocket of moisture with values near 1.3 inches north of Kauai, and drier air with values of 1 inch or less extending several hundred miles east of the state. In the large scale, an upper level trough and cold front will pass well north of the state this weekend. While the front will not reach our latitude, it will weaken and displace the high to the northeast and lead to a subtle drop in wind speeds over the next couple days /locally breezy versus the current more widespread breezy/. Forecast soundings and cross sections show only minor fluctuations in inversion height/moisture depth, leading to a relatively consistent and typical trade wind pattern for clouds/showers through the weekend. As the front and parent low pull farther away from the state, a new high will build in to our north late in the weekend, bringing another surge in trade wind speeds. Moisture left behind by the front will get picked up by the trades and enhance showers across the islands by the middle of next week. Timing is still uncertain, with extended models showing quite a spread from as early as Tuesday in the ECMWF to as late as Thursday in the GFS. It depends on exactly how the old frontal moisture interacts with the high and how quickly it moves south. Right now am leaning toward the slower GFS as it seems as though it should take longer for the moisture to work down to our latitude, but it is too early to reliably determine which is more likely at this point. Therefore will keep similar climatological pops through much of next week.

  • Aviation
    Moderate to fresh trade winds will focus clouds and light showers over the windward and mauka areas. Airmet tango remains in effect for tempo moderate low level turb over and immediately S through W of the mountains due to the trades. The will remain up through tonight and possibly Friday as well. Tempo MVFR cigs and mtn obsc will be possible late tonight for some of the windward areas, which may prompt an airmet sierra issuance.

  • Marine
    The morning ascat pass only clipped the western half of the state, and missed the area where the small craft advisory is currently in effect. However, the large area of 20 knot winds around Oahu does validate the stronger model solutions, which continue to show 25 knots through the typically windier areas. The current advisory runs through tonight, with the idea that the weakening gradient will cause winds to drop below 25 knots. The decrease in winds is less pronounced than expected before, and we will be borderline for small craft through the weekend. Will hold off on adjusting the advisory for now so we can get a look at the evening ascat pass to see how the trend in speeds is progressing. The mokapu and Hilo buoys show seas of 8-9 feet due mainly to trade swell /mainly east-northeast though the Hilo buoy is reporting more of a east-southeast direction/. This swell should gradually decrease over the next couple days as the high to the northeast weakens, then pick back up early next week as the next high builds north of the area. Small swells from the northwest and south are also in store this week. Surf along south facing shores may rise early next week as a swell from east of New Zealand reaches the islands.

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

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