Area Forecast Discussion
Issued by NWS Honolulu, HI

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000 FXHW60 PHFO 021349 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 349 AM HST Tue Mar 2 2021 .SYNOPSIS... Windy trade winds will persist through today before trending down to locally strong by Wednesday night. A new high pressure system will usher moderate to strong trades into the area during the second half of the week, and continue into the weekend. Strong and gusty trade winds will be returning by Monday and continue through the first half of next week. A wet trade wind pattern is expected Thursday night into the weekend with the aid of another upper level disturbance. && .DISCUSSION... A series of surface highs will be replacing one another through the rest of the week. The surface high north of Kauai has been taken over by a new 1044 mb surface high 1700 miles northwest of Kauai. This high will be moving east-southeast through Wednesday night to a position 1200 miles northwest of Kauai with a central pressure of 1035 mb. Into Friday this high will be taken over by a 1040 mb high located further north. This new high will move southeast to 1200 nm northeast of Kauai on Sunday. Translated, the trade winds will ease down to locally strong over the common waters of Maui County and waters south of the Big Island by Wednesday night and hold through Thursday. Trade winds will start strengthening over the waters around Kauai Thursday night and expand eastward to the rest of the area Friday, and persist through Saturday. Another boost in the trades will come Sunday into Monday. This boost may warrant a Wind Advisory for the common windy areas. The current Wind Advisory (WA) for most the islands is set to expire late this afternoon at 6 pm HST today. We will see how the winds are trending, and extend the advisory if needed for tonight. The advisory is not expected to last into Wednesday. The winds atop Mauna Kea have level off below advisory criteria, so no advisory is needed. There were some clouds moving through the summits of Mauna Kea earlier, causing a slight rise in relative humidity, but have since cleared out. Satellite imagery shows plenty of low level moisture about to cut through most of the islands. So there will be some passing showers during the morning rush. With the aid of the strong trades, many of these showers are making their way into the lee areas of the smaller islands with ease. The 2 am HST weather balloon sounding from Lihue and Hilo shows a inversion at 10 to 11k feet. This is expected to hold through Thursday. Models are indication that this afternoon to be rather dry, ahead of a band of moisture that will be moving down on the islands this evening. The clouds and showers then dissipate Wednesday morning, followed by another band of moisture. On Thursday, we will likely see the increase in trade showers, especially in the afternoon and into the night as remnants of a front moves down on the islands. These showers will have the support of an upper level trough that stall over the islands on Friday. The trough will drift down to the Big Island on Sunday. In essence, wet trades are expected between Thursday afternoon and at least Sunday. We will be taking a closer look in the days ahead to see what are the impacts of this wet and windy outlook. && .AVIATION... Strong trade winds will continue to be supported by a surface high to the N, delivering stable and showery low clouds that will focus over windward slopes and coasts, resulting in periods of MVFR VIS/CIG. AIRMET Tango remains in effect for moderate to severe low-level turbulence near and downwind of the terrain, for locally strong surface winds, and for moderate mid-level turbulence between FL220 and FL300 due to a trough aloft. Some decrease in low-level wind speed is expected tonight into Wednesday while the turbulence aloft should also diminish as the trough aloft moves E of the area. && .MARINE... Strong to locally gale force trade winds continue through today as strong high pressure holds far north of the state. A Gale Warning is in effect for the typical windier waters around the Big Island and Maui County through this afternoon. A Small Craft Advisory (SCA) remains posted for the remaining waters due to the combination of both strong trade winds and resultant rough seas. The surface high is being replaced by another surface high far northwest of the islands this morning, and commence a short- lived downward trend in the trades. The Gale Warning will be replaced by an SCA this evening. The weakening trades along with the subsiding seas result in the reduction of the SCA to waters around Maui County and waters south of the Big Island by Wednesday night. Building high pressure to the northwest of the state will bring a boost in the trades to the waters west of Kauai, thus warranting an SCA there. The SCA will likely expand eastward and join up with the SCA in effect for the Maui County waters and waters south of the Big Island. Over the weekend, the SCA will cover most, if not all of the nearshore waters. Large trade wind-driven seas will maintain high surf along east facing shores into Wednesday. Nearshore buoys have been holding at 9 to 11 feet with near 11 second periods. Fully-developed seas will continue to produce rough east shoreline surf above the 8 foot High Surf Advisory (HSA) threshold through Wednesday afternoon. As trade winds over and upstream of the islands weaken through the middle of the week, surf along eastern exposures will lower to borderline HSA levels by Wednesday evening. Expect east shore surf to be just below HSA levels late this week and during the weekend. Surf will remain below advisory levels on all other shores through Thursday. Exposed sections of both north and south-facing shores will pull in some trade wind swell wrap and keep south shore surf near winter averages today to be followed by a decline from today through Wednesday. Moderate height, long period northwest swells will begin arriving Wednesday afternoon and evening, peaking surf along north and west-facing shores late Thursday into Friday. Fortifying secondary north swells will arrive on Friday and clip the islands. While the bulk of this northern swell energy will pass to the east of the chain, there will be enough energy to keep surf at, or slightly above, HSA heights both Friday and Saturday. These swells will diminish through the weekend and lower surf below HSA thresholds by Saturday evening. && .HFO WATCHES/WARNINGS/ADVISORIES... Wind Advisory until 6 PM HST this evening for Kauai-Oahu-Molokai- Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-Maui Central Valley-Windward Haleakala-Leeward Haleakala-South Big Island-Big Island North and East-Kohala. High Surf Advisory until 6 PM HST Wednesday for Kauai Windward- Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward Haleakala-South Big Island-Big Island North and East. Small Craft Advisory from 6 PM this evening to 6 PM HST Wednesday for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. Gale Warning until 6 PM HST this evening for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. Small Craft Advisory until 6 PM HST Wednesday 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- Big Island Windward Waters. && $$

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