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Marine Weather Message in Effect for the Coastal Waters

Marine section from the Area Forecast Discussion
issued at: Apr 26, 2018 3:32 AM HST

A surface high far to the NNE will move E and gradually weaken over the next two days as a low develops about 1000 miles N of the islands. Fresh to locally strong trade winds will later today, then collapse completely tonight as a weak trough develops over the area. A Small Craft Advisory (SCA) currently posted for the windier marine zones around Maui and the Big Island will continue through the day today before the trades begin to diminish.

A front associated with the developing low is expected to reach Kauai sometime Friday, then move down the chain through Saturday before potentially stalling near the Big Island through the rest of the weekend. Initially, right behind the front, N winds may briefly reach SCA criteria in some of the marine zones. The low will send a mix of swells and seas toward the islands this weekend into next week, with associated seas rising above 10 feet in most zones, necessitating a SCA from late Saturday into Monday.

A moderate long-period NNW swell is expected to arrive today and peak Friday, with peak surf heights below advisory levels. The low that develops N of the islands late in the week will remain in place until early next week. The amount of swell/surf that arrives in the islands is somewhat uncertain, and will depend on the evolution of the low and associated fetch. Current indications are that a fairly significant (but poorly organized) swell will produce advisory-level surf along exposed N and W facing shores, with the peak of the swell around Sunday.

Elsewhere, several pulses of relatively small SW to S swell are expected over the next week or so, with a peak in swell energy around Sunday. Rough and choppy surf along E facing shores will diminish Thursday and Friday. The Oahu Surf Discussion (SRDHFO) contains further details on the sources of the swells.

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About the Marine Program

Routine forecast are issued for the Hawaiian Coastal Waters, the Offshore Waters, and High Seas. Coastal Waters are within 40 nautical miles of the main Hawaiian islands. The Offshore area extends from this 40 nautical mile mark to 240 nautical miles of the main Hawaiian islands. The High Seas forecasts are issued for an area that covers approximately 15,000,000 square miles, extends as far north as 30N, and as far south as 25S, and between 120W south of the equator and 140W north of the equator to 160E.
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The marine forecasts issued are based on marine observations and model data. Marine observations include buoy and ship reports. Ship reports are invaluable to the NWS, and are reported through the U.S. Voluntary Observing Ship Project. If you are a mariner, please consider joining the nearly 1,000 volunteer ships from around the world that observe the weather at their location.