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Menu of Text Products for the Hawaiian Islands and the Tropical Pacific/Atlantic Oceans: Select a text product: Hawaiian Islands Synoptic Discussion and Guidance Hawaiian Islands Short Term Forecast Hawaiian Islands 7-day Zone Forecast Hydrologic Outlook Flash Flood Warning Flash Flood Watch Flash Flood Statement Tornado Warning Severe Weather Statement Severe Thunderstorm Warning Special Weather Statement Winter Storm Warnings/Watches/Advisories Urgent Weather Message Marine Weather Statement/High Surf Advisory/Warning Special Marine Warning Radar Message Special Messages Unknown Terminal Aerodome Foreasts (TAFS) Area Forecast for Hawaii and Adjacent Coastal Waters Upper-level Winds and Temperature Forecast for the 4 Major Hawaii AP AIRMETs for IFR Conditions, Turbulence, and Icing Thunderstorm SIGMETs Hawaiian Islands Satellite Interpetation Message Central/North Pacific Tropical Weather Outlook Central/North Pacific Tropical Weather Summary Central Pacific Tropical Cyclone Summary South Pacific Tropical Cyclone Summary Tropical Cyclone SIGMETs Buoy Winds and Wave Forecast Oahu Surf Observation and Forecast/Coastal Forecast for Hawaiian Waters Offshore Forecast for Hawaiian Waters North Pacific High Seas Forecast South Pacific High Seas Forecast Hawaiian Islands Automated Surface Observation System Hourly Weather Roundup Hawaiian Islands Wind Data Hawaiian Islands Rainfall Summary Hawaii Temperature and Precipitation Summary Daily Hawaii Cooperative Observations Honolulu AP Climate Summary Lihue AP Climate Summary Kahului AP Climate Summary Hilo AP Climate Summary Atlantic Tropical Cyclone Discussion Atlantic Tropical Weather Outlook East Pacific Tropical Cyclone Discussion East Pacific Tropical Weather Outlook Central Pacific Tropical Cyclone Discussion Central Pacific Tropical Weather Outlook West Pacific Tropical Cyclone Discussion West Pacific Tropical Weather Outlook

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Hawaiian Islands Synoptic Discussion and Guidance 090 FXHW60 PHFO 041326 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 326 AM HST Thu Mar 4 2021 .SYNOPSIS... Fairly typical trade wind weather will persist today, with showers favoring windward and mauka areas. A surface trough will develop in the vicinity of the islands tonight and Friday, then slowly shift westward Friday night. This will bring wet trade wind conditions particularly to windward sections of the smaller islands. As the trough shifts westward over the weekend, a wet trade wind pattern will continue as the trades rebound back to breezy levels. The trades will strengthen further Monday through the middle of next week, with windy and potentially very wet conditions developing. && .DISCUSSION... Currently at the surface, a 1035 mb high is centered around 1300 miles northwest of Honolulu, and is driving moderate to locally breezy trade winds across the island chain early this morning. Infrared satellite imagery shows partly to mostly cloudy skies in most windward areas, and clear to partly cloudy conditions in most leeward locales. Radar imagery shows only a few showers moving into windward areas of the smaller islands, with shower coverage a bit greater over windward Big Island. Meanwhile, very little if any shower activity is affecting leeward locales. Main short term concern revolves rain chances during the next couple days. High pressure northwest of the islands will weaken slightly as it settles slowly southeastward during the next couple days. Meanwhile, a weak surface trough will develop along the tail end of an old front near or just north of the islands tonight and Friday. This trough will keep the tightest gradient north of the state, and maintain trade winds generally at moderate levels through Friday. As the trough shifts westward Friday night and Saturday, a new strong 1040 mb high will build north of the state. This high will then slowly settle southeastward while maintaining its strength of around 1040 mb through the middle of next week. As a result, we should see winds increase over the weekend, with windy conditions (possibly advisory level winds) in place late Sunday through the middle of next week. As for the remaining weather details, fairly dry trade wind weather is expected today, although windward sections of Kauai will likely see more shower coverage than the remainder of the state. Quite a bit of high cloud cover will be overspreading the islands as well due to an upper level trough digging to the northwest of the island chain, but the degree of opacity appears thin enough to allow for partly sunny conditions or filtered sunshine. Moisture will begin to pool along a weak surface trough developing over or just north of the islands tonight and Friday, with this trough then sliding slowly westward Friday night. This moisture combined with added instability from a trough aloft, will lead to an increase in shower coverage and intensity, particularly over windward sections of the smaller islands. Considerable cloudiness will prevail through the period due to a combination of high and low clouds. Once the surface trough shifts west of the state, we should see a wet trade wind pattern take hold. Showers will favor windward and mauka areas, particularly at night and during the early morning hours, with a few showers spreading into leeward communities from time to time. Models suggest that deeper moisture may arrive from the east and southeast Monday through the middle of next week, resulting in potentially very wet trade wind conditions across the island chain. Additionally, moisture may extend high enough to allow for a thunderstorm or two to develop over the Big Island each afternoon Saturday through Wednesday. Will hold off on mentioning thunder for now, as the most unstable conditions could slide by just to the south of the state. && .AVIATION... The band of showers that passed over the state overnight has diminished early this morning. Meanwhile, high clouds have begun to stream across the northern islands from the west. High pressure northwest of the state will allow for moderate northeast trade winds to continue to flow over the main Hawaiian Islands today but speeds are forecast to weaken a bit compared to the previous few days. Isolated to scattered showers will ride in on the trade wind flow today and impact mainly north through east sections of the islands, though most showers should remain light with only brief periods of MVFR ceilings/visibility. Models indicate that moisture will increase as a weak surface trough approaches the islands late this evening and overnight tonight. This will increase chances for showers and MVFR cigs, especially for north through east sections of the smaller islands. AIRMET Tango remains in effect for tempo moderate turbulence between FL220 and FL300 across the state as a jet aloft continues to weaken early this morning. It is likely that this upper level turbulence threat will diminish over the next couple of hours. Additionally, AIRMET Tango also accounts for moderate low level turbulence on the leeward side of mountains of all islands due to the breezy easterly trade winds, but will also wane this morning. && .MARINE... The Small Craft Advisory (SCA) has been scaled back to include only waters around Kauai, the Kauai Channel and windward Oahu waters for hazardous combined seas near 10 feet. SCA conditions may return for most waters Friday due to building seas, and extend over the weekend as the high to our north is reinforced and trades strengthen and become more widespread. Surf heights remain below High Surf Advisory (HSA) thresholds across all shores this morning. A bump in east shoreline surf will occur late Friday night into the weekend as trade wind swell increases and an arriving north swell wrap fills in. A northwest swell will continue to fill today, peaking at or just below HSA thresholds along north and west-facing shores late today into Friday. A secondary, reinforcing north swell will arrive Friday night and, in addition to the returning trade wind swell wrap, may boost north facing shore surf heights to, or slightly above, HSA heights Friday into Saturday and slowly diminish Sunday. A small, long-period southwest swell will fill in tomorrow, providing a small bump in south shore surf, and slowly decline through the weekend. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Friday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters. && $$ DISCUSSION...Jelsema AVIATION...Vaughan/JVC MARINE...Powell Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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