Swell Matrix

Area Forecast Discussion

National Weather Service Honolulu Hi

825 pm hst Mon may 25 2020


Lighter winds and mostly dry weather are expected through Tuesday, with just a few showers, mainly during the afternoon and evenings. Trade winds are expected to strengthen by Wednesday, and remain in place into next weekend, delivering brief showers to windward areas. Varying amounts of benign high clouds are expected to move over the islands from Tuesday into Friday.


Light E-SE winds will continue into Tuesday, but will strengthen and turn toward the ENE by Wednesday as a surface ridge just N of Kauai moves N. Moderate to occasionally breezy trade winds are then expected to prevail through next weekend, delivering low clouds and showers to windward areas that will favor the overnight and morning hours. However, there remains a chance for afternoon sea breezes to fuel some clouds and showers over leeward and interior areas of the smaller islands for one more day before winds increase.

Although a low aloft passing S of the islands will send varying amounts of high clouds over the islands from Tuesday into Friday, a mid-level ridge will keep the island atmosphere stable, limiting shower intensity and coverage. Even so, the daily afternoon and evening cloudiness that forms over leeward Big Island will drop some showers, with a chance for briefly moderate to heavy showers.


A weak east-northeast to west-southwest oriented surface ridge is north of the islands early this evening. The close proximity of this feature to the area is keeping the background flow light out of the east or east-southeast across the state. This weather pattern will allow the development of local land breezes over the individual islands tonight. This may clear out some of the lingering low clouds over leeward sections of the state. However, some low clouds and brief showers will be possible along windward coasts and slopes. There could be brief MVFR conditions in some of these showers, but VFR conditions will likely prevail across most of the state through early Tuesday.

With the light background wind pattern, expect local sea breezes to develop by late Tuesday morning across most of the state. This may cause clouds with a chance of showers over leeward and interior sections of the islands Tuesday afternoon. Some of the heavier showers might produce brief periods of MVFR conditions, but again VFR conditions are expected to prevail across most sections of the state.

No AIRMETs are in effect at this time, and none are anticipated through Tuesday morning.


Light to moderate east-southeast winds will hold into Tuesday over the western end of the state, which will allow land and sea breezes to develop near the coasts. Farther east over Maui County and the Big Island, moderate to fresh trade winds are expected. Fresh to strong trade winds are forecast to return by Wednesday statewide as the ridge retreats northward and strengthens. Winds may reach Small Craft Advisory levels across the typically windy waters around the Big Island and Maui Wednesday into the weekend.

Surf along north facing shores will gradually trend down Tuesday as the small, medium-period, north-northwest swell fades. An upward trend is expected Wednesday through the second half of the week due to a storm-force low that has developed around 1000 nautical miles north-northwest of the state. This swell will shift around out of the north late Thursday through Saturday as the source passes to the north tonight through Tuesday. For the extended, guidance depicts low pressure developing over the far northwest Pacific near the western Aleutians with strong breezes setting up over a large area within the 300-330 degree band relative to the islands. If this materializes, a small northwest swell will be a possibility around next Tuesday.

Surf along south facing shores will remain small into midweek with mainly a combo of south-southwest and south-southeast energy moving through. An upward trend is anticipated by Thursday night as a new, long-period, south-southwest swell arrives. This will hold through Friday, then gradually trend down over the weekend.

For the extended, latest analysis showed 962 mb low pressure passing south-southeast of New Zealand today. Satellite data reflected this and showed a large area of gales within Hawaii's swell window in this area and seas reaching the 28 to 32 ft range. WAVEWATCH III shows this source building at Pago Pago Thursday night through Friday with a peak expected there through the day Saturday. This translates to an arrival in Hawaii through the day Monday and a peak centered around the Wednesday time frame of next week.

Surf along east facing shores will remain small through the weekend.

Watches, Warnings, Advisories


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