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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 806 FXHW60 PHFO 301330 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 330 AM HST Mon Nov 30 2020 .SYNOPSIS... A weakening high pressure ridge north of the islands will keep light and variable winds with local scale land and sea breezes in the forecast through much of the work week. An upper level disturbance passing through the eastern half of the state will keep enhanced showers during the early morning hours today. Cooler and drier trends will spread from west to east starting today. Isolated to scattered showers are possible each afternoon over island interior sections, with clearing at night through Thursday. Moderate to breezy trade winds return by Friday. && .DISCUSSION... This mornings water vapor satellite imagery shows an upper level low passing through the eastern half of the state. This low will produce enough instability for a few thunderstorms over the Big Island and the eastern half of Maui County today. Local radar imagery shows scattered to numerous showers drifting into the windward slopes of each island on the waning trade winds. Drier conditions will spread from west to east across the state later today. Unstable conditions will linger over the Big Island this afternoon, as the upper low drifts southeastward, for scattered showers and possible thunderstorms. Meanwhile, the high pressure ridge north of the islands will continue to weaken as a cold front moves across the Central Pacific basin. Trade winds will diminish into the light and variable range for most areas through Thursday. Local scale land and sea breezes will develop over each island as the large scale winds diminish. Onshore sea breezes will build clouds and a few showers over island interior sections each afternoon. Land breezes, caused by overnight cooling over the land, will clear out clouds and showers during the overnight to early morning hours. By Friday morning, a high pressure system builds in north of the islands causing a return in the trade wind flow. Expect moderate to breezy trades from Friday afternoon into Saturday with more typical windward and mountain shower activity. By Sunday another cold front approaching the Hawaiian Islands from the northwest will weaken the high pressure ridge yet again, keeping the islands in a fairly dry east to southeast wind regime. Global weather models are in good agreement in the short term forecast with the upper trough moving east of the state later today allowing drier and more stable air to move in across the region. Medium range model solutions are in fair agreement at this point with several days of light winds along with cooler temperatures and lower rainfall trends through Thursday. && .AVIATION... High pressure north of the state will weaken today, allowing the trades to diminish, with sea breezes developing in many areas this afternoon. Showers will favor windward and mauka areas through the early morning hours, with a few daytime heating showers possible over the island interiors this afternoon. AIRMET Sierra remains in effect for mountain obscuration over windward sections of Kauai and Oahu. Conditions should improve in the next few hours. AIRMET Tango remains in effect for moderate upper level turbulence between FL200 and FL300. Conditions should improve by daybreak. && .MARINE... Moderate to fresh northeast trade winds will gradually shift out of the east and relax through the day as a cold front passes to north. This will result in a land and sea breeze regime statewide later today through midweek as the progressive pattern featuring a series of fronts passing to the north continues. Fresh trades could briefly return late in the week (Friday/Saturday) as a ridge noses eastward behind one of the fronts. Despite the light winds, the largest swell of the season is expected to build down the island chain Tuesday and peak Tuesday night through midweek - driving seas well above the 10 ft Small Craft Advisory threshold for waters exposed to northwest swells. Surf along north facing shores will build later today due to a mix of lingering north-northeast swell and a new north-northwest swell arriving. This new swell should peak by tonight, then gradually ease into Tuesday. The largest swell of the season is expected to build down the island chain through the day Tuesday with up to 25 second forerunners. Guidance has trended up with this event over the past few days and now depicts a peak Tuesday night into Wednesday with surf likely reaching the giant (40 ft faces or greater) category along exposed shores. Latest satellite data reflect this potential and showed a decent sized area of hurricane force winds (up to 65 kt) focused at the islands within the 310 to 320 degree directional band Saturday. Recent SOFAR drifter buoys near the fetch are recording wave heights (40-45 ft) overnight that are mostly in line with predicted levels. Impacts will include significant beach erosion with water potentially sweeping across areas of the beaches that typically remain dry Tuesday night through the day Wednesday. The best chance for water making it onto the vulnerable coastal roadways and property will be after midnight through daybreak Wednesday as the peak of the swell and daily peak tide coincide. Looking ahead into next weekend, another significant event appears possible based on the latest model cycles - that are depicting a more compact, hurricane-force low developing and lifting northeastward across the central Pacific Friday through Saturday driving seas to 50 ft. WAVEWATCH III and ensemble wave data reflect this and depict another significant swell arriving in the islands Sunday night into early next week. Forecast confidence this far out remains low and changes are likely in the coming days as conditions evolve. Surf along east facing shores will drop through the first half of the week as the trades diminish. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Bohlin AVIATION...Jelsema MARINE...Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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