FORECAST DISCUSSION

Synopsis

24 Nov 2017 06:30:00 GMT: High pressure far north of the state will keep breezy to windy trades over the islands through the holiday weekend. Passing showers will favor windward and mauka areas, with some stray showers reaching leeward areas of the smaller islands under the robust trades. A wet trade wind weather pattern is expected to develop on Sunday and continue through early next week, as deep tropical moisture moves into the area from the southeast. The wettest conditions are expected over the eastern end of the island chain.

Discussion

24 Nov 2017 06:30:00 GMT: A high centered far north-northwest of Honolulu continues to bring breezy to windy trades to the island chain this evening. Low clouds embedded in the wind flow are reaching the islands at times, bring showers mainly to the windward areas. Some clouds and showers have also affected the lee areas of the smaller islands due to the rather robust trades. In fact, winds are still strong enough to warrant a Wind Advisory for portions of Maui county and the Big Island through rest of the evening into early Friday morning. Rainfall amounts reported are modest at best, as much of the passing showers are moving quite swiftly. Latest satellite imagery revealed more low clouds are present upstream of the islands. Thus expect more passing clouds and showers for the islands through rest of the evening into early Friday morning. Lingering clouds from afternoon convection will keep lee areas of the Big Island somewhat cloudy through the rest of the evening, though clearing is expected overnight by early Friday morning. The breezy to windy trades will continue through the holiday weekend, as the current high pressure far north will be replaced by another area of strong high pressure from further north. Still expect the winds to ease ever so slightly by early Friday, and that may enough to allow the discontinuation of the Wind Advisory for portions of Maui county and the Big Island. But then, latest forecast solutions still indicate rather strong trades to prevail, so that certainly is something to consider. Regardless, trade wind weather will prevail through the holiday weekend, with passing low clouds and showers affecting mainly windward and mountain areas. Wetter trade wind weather is expected next week, as latest forecast models continue to indicate tropical moisture from the southeast will spread northwest, reaching the eastern end of the island chain on Sunday. Airmass over the islands may also become a little more unstable as models hinted some weak mid-level features may pass over the area early portion of next week. Looks like the bulk of the moisture will linger over the eastern islands, thus Maui County and the Big Island should see the most clouds and showers. Meanwhile, the rest of the islands will experience their share as well, though probably not as much as the eastern islands. Additionally, the tropical moisture will be deep enough to reach the Big Island summits. Combining with the cold temperatures aloft, winter weather may affect those summits as early as Sunday and may continue through early part of next week. Although it's too early to determine how much snow the summit areas will see, warning level amounts are not out of the question. A Winter Storm Watch will likely be required later this weekend.

Aviation

24 Nov 2017 06:30:00 GMT: Trade winds will remain strong through the weekend. AIRMET Tango remains in effect for moderate low level turbulence over and downwind of the higher terrain due to the strong winds. AIRMET Tango is also in effect for strong surface wind speeds for Lanai and portions of the Big Island. Cloud and showers will be most prevalent over windward areas, and AIRMET Sierra for mountain obscuration is currently in effect for windward parts of Molokai, Maui and the Big Island, where the showers have been particularly persistent. While some of the showers will reach leeward areas at times due to the strong trades, expect VFR conditions to prevail there.

Marine

24 Nov 2017 06:30:00 GMT: A High Surf Warning remains in effect through Friday morning for the north and east facing shores of all islands due to a very large north swell plus high wind waves due to strong to near-gale force northeast trade winds. Wave heights continue running higher than forecast by the Wave Watch III model. The longer-period swell has peaked, but the shorter-period waves have continued to increase, so combined seas have not dropped much. There will be large waves breaking in north facing harbor entrances and possibly surges in those harbors, so a Marine Weather Statement is in effect. The swell will remain quite high overnight, then slowly subside through Saturday. A new north swell starting on Sunday will peak on Monday and subside through Tuesday. Surf from this swell may reach advisory levels. A northwest swell, and yet another north swell are expected next Wednesday. A Small Craft Advisory (SCA) is in effect through Sunday afternoon for strong to near-gale force northeast trade winds and large seas due to a combination of large wind waves and the large north swell. Trade winds are expected to remain strong through the first half of next week, and a new north swell will keep the seas high, so the SCA will likely be extended further. See the latest Oahu Surf Discussion for additional details on surf and swell.

HFO Watches/Warnings/Advisories

24 Nov 2017 06:30:00 GMT: High Surf Warning until 6 AM HST Friday for Niihau, Kauai Windward, Kauai Leeward, Oahu North Shore, Oahu Koolau, Olomana, Molokai, Maui Windward West, Maui Leeward West, Maui Central Valley, Windward Haleakala, Big Island North and East. Wind Advisory until 6 AM HST Friday for Lanai, Big Island North and East, Kohala. Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters. Small Craft Advisory until 6 AM HST Saturday for Big Island Windward Waters.

Footer

24 Nov 2017 06:30:00 GMT: DISCUSSION...Hui AVIATION...Jacobson MARINE...Donaldson

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