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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 174 FXHW60 PHFO 220637 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 837 PM HST Thu Jan 21 2021 .SYNOPSIS... Strong and gusty trade winds will become especially strong over the weekend, delivering passing clouds and showers, some briefly heavy, mainly dampening windward areas. More widespread rainfall may develop early next week as winds remain strong and shift to the southeast. && .DISCUSSION... Windy and locally wet trade wind weather will continue through the weekend and into next week. The strong winds will shift slightly to the SE early next week, with increasing moisture potentially leading to more widespread clouds and showers. A broad mid- and upper-level low is nearly stationary to the S of the area, with some of the associated layered clouds aloft over the islands from Molokai eastward. Cooler than normal mid-level temperatures associated with the low are supporting a somewhat unstable island atmosphere, with radar VWPs indicating the low-level moisture riding in on the trade flow extends as high as 10 thousand feet. With fresh to locally strong trade winds being supported by a 1035 mb high to the distant NE, island slopes are efficiently creating rainfall, even when upstream skies contain little. A perfect example is the near non-stop light rainfall over windward portions of E Maui and Oahu's Koolau mountains over the past couple of hours, as depicted by radar. Some of these showers have been briefly heavy due to their increased vertical depth and the efficiency of warm rain processes. Meanwhile, many leeward communities remain dry, not having received any recent rainfall. While some drying of the upstream flow tonight and Friday may lead to some reduction in windward rainfall, it is not expected to last long, and little overall change to the current regime is anticipated through the weekend. Mid-level temperatures will remain cooler than normal, and strong trade winds will strengthen as the high to the distant NE moves closer to the islands. A Wind Advisory may be required for parts of the state over the next couple of days, potentially as early as Friday. The high to the NE will be reinforced Saturday and Sunday, reaching a central pressure over 1040 mb, while a deep-layer low develops to the distant W and NW of the islands. This is expected to cause the winds to veer to the SE, while a moisture convergence band extending SE from the distant low creeps towards the islands from the S. Latest guidance indicates the potential for this band to move over portions of the islands from Monday into Wednesday, bringing widespread layered clouds and rainfall. A drying trend is loosely expected thereafter as the band shifts W of the area. High pressure to the distant NE will continue to support locally strong trade winds. && .AVIATION... Breezy to locally strong trades have developed and will persist through the forecast period. This will facilitate frequent windward showers and occasional leeward drift, particularly overnight. VFR is forecast to prevail at all forecast points with nothing more than brief MVFR within any heavier showers. AIRMET Tango is in effect for mod mechanical lee turbulence below 9kft as well as for mod turbulence between FL250 and FL300. && .MARINE... Surface high pressure is centered far to the north-northeast of the area, resulting in moderate to locally strong trade winds. A Small Craft Advisory (SCA) is currently posted for the typically windy waters around Oahu, Maui County and the Big Island. The high will get a reenforcement this weekend into early next week,causing trade winds to increase across the entire area. This, combined with higher seas from both a large northwest swell and the trade wind seas, will result in SCA conditions statewide. A small northwest swell will linger through Friday. Long-period forerunners from a larger northwest (310 degrees) swell will fill in late Friday and Friday night. This swell is expected to peak on Saturday with an 18-second period and high-end advisory or low-end warning level surf, then lower gradually Sunday and Monday. Surf is then forecast to become rather small for this time of year on Tuesday and Wednesday. As the trades strengthen this weekend, rough and short-period surf will gradually rise, and a High Surf Advisory is likely along east facing shores for several days. Small, mainly background, southerly swells are expected over the next several days. A slightly larger, south-southwest swell from the Tasman sea is expected to gradually fill in on Monday, peak Monday night and Tuesday, then lower Wednesday through Thursday. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Birchard AVIATION...JVC MARINE...TS Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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This page was last modified on: Wed, Dec 17 2014 - 1841 UTC
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