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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
    Trades will weaken to a land and sea breeze pattern this weekend as a cold front and upper trough approach from the northwest. North to northeast winds and rainfall will increase late Sunday night with the potential for heavy rain and thunderstorms Monday evening into Tuesday.

  • Discussion
    Satellite imagery shows a positively-tilted upper level trough over Hawaii with a west to east oriented jet stream running just south of the Big Island indicated by a swath of cirrus clouds. At the surface, high pressure is centered to the east-northeast of the state producing moderate east-southeast winds, with the strongest winds near Maui county and the Big Island. Radar and weather observations are showing trace amounts of showers this afternoon. The surface high is expected to move east, away from Hawaii, tonight and will result in progressively less influence on our winds. Meanwhile, a strong cold front is approximately 1300 miles northwest of Kauai moving toward us. The front is supported by an upper trough which will stay with it as approaches the Hawaiian islands. Winds will weaken and veer southeasterly on Saturday ahead of this system, resulting in a shift to more warm and muggy conditions this weekend. Winds will likely stay too easterly near the Big Island to bring vog up to the smaller islands. The weakening flow will also allow a sea and land breeze pattern to set up Saturday and Sunday, resulting in daytime cloud build ups over the islands and clearing out at night. Weak ridging aloft and generally dry conditions over the state this weekend will keep the afternoon shower activity on the light side. The cold front will arrive on Kauai late Sunday night / early Monday morning, followed by the cold pool aloft from the upper trough Monday evening. Northeast surface winds will drastically strengthen along the frontal boundary beginning on Kauai late Sunday night, spreading eastward down the island chain through Tuesday night. With significant support from the low / trough aloft, the front will have the opportunity to produce locally heavy rain and thunderstorms. The GFS and ECMWF models are in fair agreement through Tuesday morning, but begin to diverge solutions in terms of placement of this upper level feature. Both models bring the trough axis across Kauai Monday night, with 500 mb temperatures near -16 degrees celsius for the GFS and -17 degrees celsius for the ECMWF. The GFS forms a cut off low and brings it over the Big Island on Tuesday and Tuesday night, while the ECMWF lifts the low to the north of the state. Given the strong divergence in solutions, it is hard to say with much certainty right now where the impacts of instability caused by the upper low will occur. For now, it looks like the northwestern end of the state, namely Kauai and Oahu, would have the best chances for thunderstorms and heavy rainfall Monday night and Tuesday. The strong vertical wind shear will improve the ventilation of any thunderstorms that do develop, potentially allowing some to become severe, though remains a bit early to consider a severe thunderstorm watch. If the GFS solution holds, and the upper low tracks over the Big Island, it would draw up deep moisture bringing the potential for snow over the summits of Mauna Kea and Mauna Loa Monday night through Tuesday. As mentioned, there still a bit of discrepancy between long range model solutions. We will continue to monitor for better agreement and forecast confidence during the second half of next week.

  • Aviation
    With a front approaching and high pressure north of the islands being pushed eastward, trades will be replaced with a more southeast wind flow into Saturday. But the front will be weakening as it nears the state thus instead of strong SE winds, may see more land/sea breezes from time to time. Thus expect more interior cloudiness during the afternoons along with clearing at night with slightly less windward cloudiness. Bottom line, expect mostly VFR conditions to prevail into Saturday.

  • Marine
    The current northwest swell will continue to lower through Saturday night. A larger northwest swell is expected to arrive on Sunday and will likely build to high surf warning level heights for north and west facing shores by late in the day. This swell should have enough westerly component to impact the west side of the Big Island, likely reaching warning levels for Kona Sunday night through Monday night. East-southeast winds are expected to taper off tonight as a cold front approaches the state from the northwest. The front will push the subtropical high northeast of the state further away to the east. Winds will remain light on Sunday as the northwest swell builds, but north to northeast winds will drastically increase Sunday night into Monday as the swell peaks. A small craft advisory /sca/ is in effect through 6 am Saturday for our typical windy zones around Maui county and the Big Island, except for maalea bay due to the east-southeast wind direction. The SCA will likely be dropped Saturday morning.

  • HFO Watches/Warnings/Advisories
    Small craft advisory until 6 am HST Saturday for Maui county windward waters, Pailolo channel, Alenuihaha channel, Big Island windward waters, Big Island leeward waters, Big Island southeast waters.

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