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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 7-day Zone Forecast Hydrologic Outlook Flash Flood Statement Terminal Aerodome Foreasts (TAFS) Area Forecast for Hawaii and Adjacent Coastal Waters AIRMETs for IFR Conditions, Turbulence, and Icing Central/North Pacific Tropical Weather Outlook 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

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Hawaiian Islands Synoptic Discussion and Guidance 917 FXHW60 PHFO 201355 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 400 AM HST Mon Aug 20 2018 .SYNOPSIS... A drier airmass will persist across the state through Tuesday, with trade winds strengthening. For the remainder of the week, the forecast will be highly dependent on the track and intensity of Hurricane Lane. An increase in winds and showers will be the likely result based on the latest forecast for Lane. && .DISCUSSION... Please note that tropical cyclone operations are in effect. So as to incorporate the latest forecast information from the Central Pacific Hurricane Center (CPHC), public forecast updates from the Honolulu Forecast Office will come shortly after forecast updates from CPHC, namely after 5 and 11 am/pm, instead of the normal 4 am/pm. Drier airmass has spread across the state since last night, though early morning Lihue sounding only indicated a slight drying, while Hilo sounding has a more typical trade wind weather type profile. Latest radar data revealed not much showers, though satellite imagery, even with some high clouds obscuring, indicated there are embedded low clouds just upstream east of the islands. A surface high pressure far northeast of the state providing the trade winds continues to drop south-southwestward. Meanwhile another high pressure far northwest of the state is advancing east as well. This will allow a tightening of pressure gradient across the area, resulting in an increase in trade winds for the state. Regardless, the more typical trade wind weather is back across area, with passing low clouds and showers affecting mainly windward and mountain areas. High clouds will stream over the area at times today and will keep skies a little more opaque at times. The aforementioned two highs will gradually merge and take up a position far to our north by Tuesday. This will lead to a further strengthening in trade wind speeds across area. The somewhat drier and more stable airmass will persist in the as well. Therefore, expect breezy trade wind weather for the islands Tuesday, with passing low clouds and showers affecting mainly windward and mountain areas. Lee areas of the smaller islands may also see some clouds and showers as winds may be strong enough to carry them over. As for Wednesday through the weekend time frame, our weather will be highly dependent on the track and intensity of Hurricane Lane. It is still too early to determine the weather impacts from Lane will have on the state. The last forecast track from the Central Pacific Hurricane Center still has Lane passing south of the main Hawaiian Islands, but has it tracked closer to the island chain. If this track holds, the potential impacts on the islands weather would be an increase in wind speeds due to a tightened pressure gradient between high pressure north of the state and Lane traversing to our south. Also moisture associated with Lane would likely bring an increase in shower activity over the Big Island Wednesday, mainly east and southeast and then eventually spreading up the island chain through the remainder of the week. Everyone is encouraged to monitor the latest advisories on Hurricane Lane from the Central Pacific Hurricane Center. && .AVIATION... A high pressure ridge north of the islands will produce stronger trade winds today with with improving weather trends as drier more stable air moves in from the east. No AIRMETs in effect. As winds strengthen and the atmosphere becomes more stable this afternoon, turbulence in the lee of the mountains may become moderate and AIRMET Tango may be needed. && .MARINE... Please note that tropical cyclone operations are in effect. So as to incorporate the latest forecast information from the Central Pacific Hurricane Center (CPHC), marine forecast updates from the Honolulu Forecast Office will come shortly after forecast updates from CPHC, namely shortly after 5 and 11 am/pm, instead of the normal 4 and 10 am/pm. A weak surface trough W of Kauai will move W away from the area today and tonight as high pressure builds to the N. This will result in a gradually increasing trade wind flow through Tuesday. A Small Craft Advisory (SCA) has been posted for the windier areas around Maui and the Big Island in anticipation of the increasing trade wind flow. As Hurricane Lane moves into an area S of the islands by mid-week, the pressure gradient will likely increase, likely leading to increasing trade winds, and potentially an expansion of the SCA. More significantly, Tropical Storm and/or Hurricane Watches may be required for portions of the southern coastal waters later today. There is significant uncertainty regarding the position and intensity of Lane later in the week, so it is too early to determine what impacts Lane may eventually bring, and mariners need to continue to closely monitor forecasts. Long period ESE swells from Hurricane Lane are building at buoy 51004 to the SE of the Big Island this morning, while the PacIOOS buoy in Hilo is just beginning to detect long-period energy from the E. A High Surf Advisory for E facing shores of Maui and the Big Island is now in effect. As Hurricane Lane moves into an area S of the islands later this week, S swell will likely increase, with a wide variety of wave periods leading to rough and potentially damaging surf. Still significant uncertainty and difficult to know the level of impacts, but there is potential for large seas/swells from Lane to lead to warning-level surf along E through S facing shores of the islands. A small NNW swell is expected to arrive Monday and peak on Tuesday before gradually diminishing Wednesday and Thursday. See the latest Oahu Surf Discussion (SRDHFO) for more details on surf and swell. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 PM HST Tuesday for Windward Haleakala- South Big Island-Big Island North and East. Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ SYNOPSIS/DISCUSSION...Hui AVIATION...Bohlin MARINE...Birchard 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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