Swell Matrix

Area Forecast Discussion

National Weather Service Honolulu Hi

1000 am hst Tue Nov 12 2019


Light trade winds will prevail through tomorrow, then shift out of the south Thursday and Friday as a cold front advances toward the state. Through tomorrow, clouds and showers will favor the typical windward and mauka locations, though afternoon sea breezes will produce spotty showers over interior sections. Rain chances will trend up this weekend as the front approaches the western end of the state and a weak trough moves into the area from the east.


Weak trade winds will persist through tomorrow. The subtropical ridge driving the trades remains weakened and displaced southward to about 250 miles north of Kauai, where it will remain through tomorrow. As a result, trades will remain light enough to be overpowered by local overnight land breezes and afternoon sea breezes. Expect modest showers to favor windward slopes, while afternoon sea breezes produce clouds and a few showers over interior sections. For today, Kauai could see a few more showers due to a diffuse band of low-level moisture parked nearby. A ridge aloft is slowly building overhead from the west, which will produce somewhat stable conditions that should inhibit heavy showers over most areas.

Winds will gradually veer southerly on Thursday and Friday as a front advances toward the state. A somewhat dry and stable land and sea breeze pattern should persist on Thursday, with spotty afternoon showers favoring interior sections. Shower chances will increase on Friday over portions of the island chain. Expect some increase in showers ahead of the front near Kauai, and a trough moving in from the east may provide a boost to rainfall over the Big Island later in the day.

Wetter conditions are expected during the weekend, though details remain somewhat uncertain. The front will stall near Kauai, likely providing an increase in rainfall for the western end of the state. Meanwhile, moisture associated with the surface trough will spread westward from the Big Island, producing increased rain chances for the eastern end of the state.


Light trades will continue to focus clouds and showers along windward slopes and coasts through late this morning. Sea breezes are expected to overcome these light winds, leading to clouds and isolated showers developing over interior sections of the islands. Brief periods of MVFR conditions are possible in the heavier showers. Land breezes will clear out the clouds and showers over these areas overnight.


Light easterly winds will prevail through Wednesday as a weak area of high pressure passes eastward just north of the area. Light southerly flow will gradually develop later in the week as a front approaches from the northwest. Winds are expected to swing around to a more northerly direction on Saturday as the front moves over portions of the forecast area. Wind speeds will remain below Small Craft Advisory levels.

The current northwest swell will continue to lower today through Wednesday. A larger north northwest swell is expected to arrive on Thursday, peak Thursday night, then lower gradually Friday and Saturday. A High Surf Advisory will likely be issued for this swell for most north and west facing shores.

A larger northwest swell is expected to arrive on Saturday, peak Saturday night, then lower gradually Sunday and Monday. Surf heights may reach low end warning levels during the peak of this swell.

A series of small southerly swells are expected through the remainder of the week and on through the weekend. Surf will remain small along east facing shores due to the light winds over and upstream of the state. Surf heights will likely rise by early next week as high pressure build in to our north.

Watches, Warnings, Advisories


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