Big Picture

BIG Picture updated 4pm, Sunday, April 21

Monday, April 22nd – Tuesday, April 30th

NE-ENE trades shifting East this period…

Surface ridging extended from the US west coast to the subtropics of the central North Pacific, and weaker storm activity prevailed over the western Pacific over the weekend, a sign of the gradual transition to the summer season. Closer to home, an area of high pressure was centered 600 nautical miles north of Hawaii and brought moderate (10-20mph) ENE trade winds. Over the next few days, a longwave surface trough over the western North Pacific will sharpen and nudge the high pressure center eastward. As a result, trades by mid-to-end week should shift East and ramp to fresh paces (15-25mph). By the weekend and early next week, the trough will approach the islands and should cause trades to weaken to moderate paces. Windward and mauka showers associated with the trade flow should return late Monday and persist through the period.

Surf Outlook –

North and West Shores: Small surf prevailing this period with peaks nearing the moderate category…

Recent/Now/Next: Surf on Sunday was 3-4’+ Hawaiian scale from the NNW in the 12-14 second period band. The source was a nearly stationary, broad area of low pressure over the Gulf of Alaska that directed a wide fetch of 30-40mph winds at Hawaii Apr 17-18. Surf should drop from 2-4’ early Monday to 2-3’ in the afternoon and 1-2’ on Tuesday.

Next: A compact low quickly deepened to storm-force east of Honshu Apr 18-19 as it pulled NNE. It then stalled off the coast of Hokkaido Apr 19-20 and gradually weakened. Long period forerunners of 17-18 seconds from the WNW should arrive pre-dawn Tuesday. Surf should slowly rise to 1-2’ early Wednesday, just in time to keep the waters from going flat as the NNW swell fades to zilch. Heights should tick up another notch on Thursday to 2-3’ from a more WNW-NW angle. Surf should drop to 1-2’+ early Friday.

Finally: The almost dissipated storm will merge with a cyclone centered over the western Bering Sea Apr 22-23, causing it to intensify and nudge southward. This nudge will place a short portion of its western flank south of the Aleutian Islands, enabling fetch of 40-50mph winds to generate predicted seas of 24-28’ towards Hawaii. 17-19 second period forerunners from the NW-NNW should arrive overnight Thursday. Surf should rise to 2-3’+ early Friday and 2-4’+ in the afternoon. It should peak overnight and drop to 2-4’ early Saturday, 1-2’+ early Sunday, and 1-barely 2’ early next week.

Outlook: As is typical for this time of the year, the North Pacific looks to go quiet Apr 24-29. Trade wind swell wrap should become the dominant source of surf. This would translate to tiny surf of 2’ or less for the final week of April and the first week of May.

South and West Shores: Smaller surf from the SW-SSW this period…

Recent/Now: Surf on Sunday was above the summer background level but below the summer average at 1-2’ occ. + from the SW at 13-15 second periods. There was also a smidgen of short to moderate period SSE swell on its way out. The source of the SW swell was plenty storm activity west and south of the Tasman Sea that aimed long, wide fetches of 40-50mph winds to the ENE Apr 14-17. Surf should hold at 1-2’ occ. + into early Wednesday and drop to below the summer background level (2’ or less) by Thursday. The South Pacific went quiet Apr 18-21. Heights should hold at 1-1.5’ from Thursday to the weekend.

Finally: Models depict a weak storm stretching from SE of New Zealand to the subtropics Apr 22. Winds along this area could reach 35-45mph. It could bring a small SSW swell early next week with surf peaking at near 2.5’.

Outlook: The long range shows moderate-intensity systems tracking along the mid-high latitudes of the South Pacific. A series of storms passing south of the Tasman Sea could bring surf from the SW to near the summer background level (1-2’) for the first week of May. All eyes then turn to a large, stronger storm south of New Zealand May 1-4 and possibly beyond that could deliver a long-lived surf episode at near the summer average (1-2’ occ 3’) beginning towards May 8.

East Shores: Rising, bumpy trade wind swell this week…

Recent/Now/Finally: Surf on Sunday was 1-2’+ from a mix of North swell wrap and 6-7 second period ENE trade wind swell. Surf from the North wrap should drop on Monday. As the upstream and local trades strengthen over the next few days, trade wind swell will rise. Surf from the wind swell should rise to 1-2’+ on Monday and 2-3’ Tuesday through midweek. It could peak locally at 2-3’+ on Thursday as the swell period rises to 8 seconds. Surf should hold at 2-3’ on Friday and steadily drop over the weekend as the local winds ease. Heights should be down to 1-3’ early Saturday, 1-2’+ early Sunday, and 1-2’ early next week.

Outlook: The is fair confidence that the trade wind regime will rebound around the start of May, and surf should rise to near or above average (3’+) for the first weekend of the new month.

The next full SNN Big Picture will be issued on Sunday, Apr 28.

Forecaster Jonathan Huynh

Surf Climatology HERE

NEW NWS criteria for High Surf Advisories (first number) & Warnings (second number).

All surf height observations & forecasts are for full ‘face’ surf height, or ‘trough to the crest’ of the wave.

North-Facing Shores 15 Feet and 25 Feet

West-Facing Shores – Remaining Islands 12 Feet and 20 Feet

West-Facing Shores – Big Island 8 Feet and 12 Feet

South-Facing Shores -(Advisory) 10 Feet (up 2′) and (warning) 15 Feet

East-Facing Shores – 10 Feet (up 2′) and 15 Feet

Get the latest Central Pac Hawaii HERE

For the SNN Buoys ‘per shore’ displayed   HERE

Note: Spectral density graph in the SNN Buoy Page HERE can show ‘slivers’ of forerunners that initial text readings of new swells which often do not ‘show’ till later on written/text buoy updates.  Also, note the vertical graph is not ‘wave height’ rather its a measure of wave energy in hertz (frequency or cycles/sec) for the whole ‘band’ (the distribution of power/period in the total wave energy field/spectrum).

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