Swell Matrix

Area Forecast Discussion

National Weather Service Honolulu Hi

816 pm hst Mon Jan 17 2022

Synopsis

Generally dry and pleasant weather and light winds can be expected through most of the week. A few showers will be possible over windward slopes and coasts, mainly over the eastern islands during nights and mornings, with a few showers developing over the island interiors each afternoon. A weakening front may bring an increase in showers late Friday through Saturday night as it moves down the island chain, particularly for windward areas. Drier weather appears to build in behind the front for Sunday and next Monday, with minimal shower activity.

Discussion

Currently at the surface, a 1024 mb high is centered around 1400 miles northeast of Honolulu, with a ridge axis extending southwestward to a location near or just north of Kauai. Light winds are present statewide, with land breezes developing in most areas. Infrared satellite imagery shows clear to partly cloudy conditions in most areas, with a bit more cloud cover over the Big Island slopes. Radar imagery shows very little shower activity statewide. Main short term concern revolve around rain chances during the next few days.

The ridge of high pressure will remain nearly stationary near or just north of Kauai through Thursday, before settling southward over the islands Thursday night and Friday as a front approaches from the northwest. This will keep light and variable winds in place featuring overnight land breezes and daytime sea breezes for the western islands, with light to locally moderate trade winds prevailing over the eastern end of the state. The front is forecast to move southward into Kauai Friday night then push southward through the remainder of the island chain Saturday and Saturday night, while high pressure builds in north of the state. Light trade winds could make a return as early as Friday night, with moderate trades then filling in over the entire state over the weekend and holding in place through early next week.

As for the remaining weather details, fairly dry conditions will continue through the remainder of the work week. A few showers will be possible over the windward slopes and coasts during nights and mornings, mainly over the eastern end of the state, while a couple showers will be possible each afternoon over the island interiors. Shower coverage and intensity may be a bit higher on Friday over Kauai as some deeper moisture appears to move in here in advance of the front. As the front moves down the island chain Friday night through Saturday night, we should see an increase in shower coverage, particularly over windward slopes and coasts. Drier weather appears to build in behind the front for Sunday and next Monday, with minimal shower activity.

Aviation

Satellite and sfc obs are showing limited cloud cover across western sections of the state this evening. However, over the Big Island and Maui, satellite is showing sea breeze clouds which developed during the afternoon, diminishing in areal coverage and beginning to push off the coast as the transition to land breeze begins.

Otherwise, sfc and upper lvl ridging anchored over the islands, will continue to limit the chances for showers through Tuesday afternoon, while allowing for the continued diurnal sea and land breeze circulations to dominate the region. This pattern will allow for sea breeze cloud and showers over interior sections and along slopes Tuesday afternoon. The transition to land breeze and decreasing cloud cover will once again be noted Tuesday evening. VFR conditions are expected through the TAF period, though there is a brief chance for MVFR cigs developing in heavier showers.

Currently no AIRMETs are in effect. However, AIRMET Tango could be required later Tuesday for a potential period of mod upper lvl turb.

Marine

A weak surface ridge axis centered over the island chain has kept very light winds in place across most of the local waters today. A couple of cold fronts moving down from the northwest this week will do little to the ridge in terms of movement. The result will be light and variable breezes over the western end of the state and light to moderate southeasterlies over eastern waters through Friday. The passage of a couple of large, west-northwest swells may push combined seas above Small Craft Advisory criteria Wednesday and then again Friday evening through next weekend over exposed waters.

The nearshore buoys continue to show a downward trend, with sub- advisory surf into Tuesday. The forecast guidance still indicates a reinforcing west-northwest swell, very similar to this past weekend, will arrive Tuesday and gradually build through Tuesday night, with a peak Wednesday. Surf generated by this swell is expected to reach High Surf Advisory (HSA) criteria along most north and west facing shores of the smaller islands late Tuesday and Wednesday. With its slightly more westerly direction, this swell could push surf to or above the 8 foot HSA criteria along west facing shores of the Big Island Tuesday night through Wednesday. This swell will gradually lower Thursday before the initial forerunners from a larger west-northwest swell arrive early Friday. This swell is expected to rise rapidly, with resulting surf likely exceeding High Surf Warning (HSW) thresholds along most north and west facing shores of the smaller islands from as early as Friday afternoon, but most likely that evening. An HSA will likely be required for the west facing shores of Big Island Friday night as well, with a possible HSW by early Saturday morning.

Watches, Warnings, Advisories

None.

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