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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 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 Daily Hawaii Cooperative Observations

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Hawaiian Islands Synoptic Discussion and Guidance 044 FXHW60 PHFO 180646 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 846 PM HST Wed Aug 17 2022 .SYNOPSIS... A ridge of high pressure north of the state will lift northward and allow for a gradual strengthening of the trade winds during the next couple days. Showers will favor windward slopes and coasts tonight and early Thursday, before transitioning over to leeward and interior areas Thursday afternoon. A more typical, but drier than normal trade wind pattern will return Thursday night and hold through the weekend, with moderate to locally breezy conditions prevailing. A mid and upper level trough will bring some deeper moisture and an increase in trade wind showers as it moves into the region during the first half of next week, while the trades gradually ease into the light to moderate range. && .DISCUSSION... Currently at the surface, a 1022 mb high is centered around 1600 miles northeast of Honolulu, with a ridge axis extending west- southwest to a location around 300 miles north of Kauai. The resulting gradient is producing light trades over the western islands, while moderate trades prevail over the eastern end of the state. Infrared satellite imagery shows partly to mostly cloudy conditions, with cloud cover decreasing in most areas with the loss of daytime heating. Radar imagery shows isolated to scattered showers moving into windward areas, a few lingering showers over leeward sections of the Big Island, and mainly dry conditions elsewhere. Main short term focus revolves around trade wind trends and rain chances. The ridge of high pressure north of the state will lift northward during the next couple days, resulting in an increase in trade wind speeds across the island chain. Moderate trades will prevail tonight and Thursday over the eastern islands, while light to locally moderate trades hold over the western end of the state. The trades will likely be light enough over Kauai and Oahu for some land and sea breezes to develop in the more sheltered leeward areas during this time. The trades will increase to moderate and locally breezy levels Thursday night, then hold steady Friday through the weekend. A front dropping southward toward the islands early next week, should ease the trades to moderate levels on Monday, and into the light to locally moderate range Tuesday and next Wednesday with some land and sea breezes possible in the more sheltered leeward areas. As for the remaining weather details, we should see a gradual increase in trade wind showers overnight, with the coverage the greatest over the eastern end of the state. Most leeward areas will remain dry, although a few showers will remain possible over leeward Big Island through the night. Showers will continue to favor windward areas Thursday morning, before transitioning over to leeward and interior locales Thursday afternoon. Lingering instability over the Big Island could allow for the development of a thunderstorm or two Thursday afternoon as well. The daytime convective showers should end quickly Thursday evening, with a more typical trade wind pattern then taking hold featuring primarily windward and mauka showers. Rather dry trade wind weather will then prevail Friday through the weekend, with showers limited primarily to windward slopes and coasts. We should see an increase in trade wind showers during the first half of next week as a mid and upper level trough and some associated deeper moisture moves in from the east. && .AVIATION... The trade winds are trying to strengthen over the eastern end of the island chain. However, the background flow remains weak enough to allow local land breezes to become established over most of the islands. These downslope winds are expected to clear out most of the residual clouds and showers over leeward and interior sections of the islands this evening. The weak trade wind flow will transport some low clouds and brief showers into windward facing coasts and slopes through Thursday morning. Brief MVFR conditions may develop over some windward sections overnight, but VFR conditions will likely prevail. Expect Thursday to be a transition day, with the trade winds gradually returning to the entire island chain. The strongest trade winds will initially be over the eastern islands Thursday morning. The weaker trades near Kauai and Oahu may allow some local sea breezes to develop starting late Thursday morning over the leeward sections of the western islands. However, expect moderate to locally strong trade winds over most areas by late Thursday afternoon or evening. The trades will carry some low clouds and showers into windward sections of the islands. This may produce brief MVFR conditions, but VFR will be the general rule for most areas on Thursday. No AIRMETs are currently in effect, and none are anticipated through Thursday morning. There is a possibility that as the low- level trade wind flow strengthens late Thursday, AIRMET Tango for mechanical low-level turbulence may eventually be required for portions of the state starting Thursday afternoon or evening. && .MARINE... A weak ridge persists north of the islands and will sustain light to moderate trade winds. The ridge will strengthen and shift north, causing trade winds to increase beginning Thursday morning through the afternoon. A Small Craft Advisory will likely be posted across the typically windier waters around Maui County and the Big Island when warranted. Small south and southeast swells are expected to produce below typical summertime surf heights along south facing shores into Friday. Forerunners from a new, long-period south swell are expected to arrive late Friday night. This swell will likely produce near to slightly above average surf along south facing shores from this weekend into early next week. Surf will remain small along east facing shores until trade winds strengthen. As they do, modest, choppy surf will return along east facing shores, lasting from this weekend into early next week. Expect nearly flat conditions to persist along north facing shores through tonight. Small, short-period north-northwest swells beginning Thursday may provide a slight boost in surf heights along exposed north facing shores through this weekend. Models show a slightly larger and longer period northwest swell arriving early next week. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Jelsema AVIATION...Houston MARINE...Kinel 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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