Big Picture

BIG Picture updated 545pm, Sunday, March 17

Monday, March 18th – Tuesday, March 26th

Gradually increasing trade winds through the week…

The large-scale pattern over the North Pacific is progressive, characterized by a 150-170mph jet stream extending from Honshu to Baja California. At the surface level, this setup has led to relatively weak ridging over the central Pacific. As a result, light to moderate (10-15mph) NE trade winds prevailed over the weekend, light enough for sea breezes over leeward coasts. These NE trades will shift ENE on Monday as a front to the NW nudges the ridge eastward. The front will wash out on Tuesday, allowing for a new ridge to build in from the west. Trades should shift NE on Tuesday and then increase to moderate paces (10-20mph) midweek. Speeds should reach moderate to fresh paces (10-25mph) by Friday and Saturday as the ridge peaks. Towards Sunday, a disturbance passing south of the island chain should cause winds to both veer E-ENE and ramp to fresh paces (15-25+mph). The local pattern becomes unclear next week as models diverge in trade wind intensity.

The weather will remain rather dry through Thursday. By Friday, remnant moisture from a front could be advected over the islands and bring increased light shower coverage. Mostly dry weather should return for the weekend.

Surf Outlook –

North Shore and West Shores: Multiple, significant swells to pound the North Shores this period…

Recent/Now/Next (MODERATE TO LARGE): On Sunday afternoon, moderate to large surf of 5-7’+ Hawaiian scale was brought by a filled-in, 16-18 second period WNW swell and a diminishing, 10-11 second period NNW swell. The latter swell was generated by a storm-force low that tracked favorably SE from just south of the central Aleutian Islands. The track led to a captured fetch of 40-50mph winds aimed directly at Hawaii Mar 12-13, leading to surf that reached XL levels of 12-15’+ (25’+ faces) last Thursday and Friday. Surf from the NNW swell should drop to 1-3’ on Monday, which will be well smaller than the WNW swell. That swell was generated by a large, near-hurricane force system that slowly tracked NE and parallel to the Kuril Islands over the NW Pacific Mar 12-14. Surf from this swell should hold at 5-7’+ early Monday and slowly drop through the day. Heights should be 3-5’ early Tuesday.

Next (LARGE): Next up was a more compact low that rapidly deepened to well into hurricane-force strength (75-90mph) and tracked straight east over the NW Pacific Mar 16-17. These extreme winds were captured over a distance of 650 nautical miles and generated satellite-confirmed seas of 38’ to within 2,100nm of Hawaii late Saturday night. These seas extended closer to the state than modelled by WaveWatch III. Extra-long period forerunners of 21-23 seconds from the WNW-NW should arrive after midnight Monday. Surf from this swell should steadily rise from 1-3’+ at dawn Tuesday to 5-8’ by dusk. It should peak just before dawn Wednesday at 8-12’ (20’ faces). This will be big enough to feather the outer reefs with only the largest nearshore spots such as Pipeline and Sunset in play. Makaha should peak at 5-7’ (12’ faces). There is a small chance that the JASON-3 altimeter swath missed the largest seas, in which case the resulting surf could be larger than stated here. Global models historically have had a tendency to underestimate such extreme winds. Surf should drop to 8-10’ by late afternoon, 4-6’+ early Thursday, and 2-3’+ early Friday.

Next (MODERATE TO LARGE): Another strong storm is predicted to quickly follow on the heels of the hurricane-force low. This larger storm should aim a long, very wide area of 45-60mph winds from Hokkaido Mar 18-19. Compared to the previous system, this one will be larger but weaker and farther away. Very long period forerunners of 19-21 seconds from the WNW should arrive after midnight Thursday. Surf should steadily rise from 1-2’ early Friday to 4-6’ by late afternoon. Heights should peak on Saturday at 6-8’+ and drop to 4-6’+ early Sunday.

Finally (LARGE): Models have been advertising an even large, stronger storm emerging from central Honshu and tracking ENE towards the central Aleutians Mar 20-22. This system could bring a WNW swell comparable in size to that of Wednesday. Extra-long period forerunners of 22-25 seconds from the WNW could arrive Sunday morning. Surf could rise to 5-7’ before dark (3’ of swell with a 20 second period). It could peak on Monday at 8-12’.

Outlook: As the northern hemisphere gradually transitions to spring, there are hints that the North Pacific could simmer down a few notches towards the last week of March and the start of April. Surf of at least moderate size (up to 6’) still appears to be a good bet on peak days, but this would be much smaller than compared to that of the first three weeks of March…

South Shore: Above summer-average surf on Monday followed by another similarly sized event next week…

Recent/Now: Surf on Sunday afternoon was 1-2’ occ. + from the SSW. The source was a large, unusually powerful storm for this time of the year that tracked eastward and south of New Zealand Mar 9-10 with 50-65mph winds aimed favorably to the NE. A satellite altimeter measured seas to over 38’ which is on par with WaveWatch III output early Mar 11. Surf should peak above the summer average at 1-2’ occ. 3’ on Monday, the largest South-hemi event of the year so far, and slowly drop later Tuesday. It should be 1-2’ on Wednesday and 1-occ. 2’ on Thursday.

Next: A series of much less impressive systems aimed 30-40mph winds at the Tasman Sea and just east of New Zealand Mar 11-14. It could keep background level surf of 1.5’ from the SW-SSW Thursday to Sunday.

Finally: A longwave trough began to aim a fetch of 25-35mph winds to the NNE-NE from SE of New Zealand Mar 17. The area of disturbed seas from this weak fetch should be captured by a subtropical storm centered 600nm east of northern New Zealand Mar 19-22. Short to moderate period energy from the SSW could arrive late Sunday. Surf could rise to 1-occ. 2’ on Monday and 1-2’ occ + early Tuesday as the period increases. It could peak at 1-2’ occ. 3’ late Tuesday into Wednesday.

Outlook: Surf should steadily drop overnight Wednesday and Thursday with background level surf likely to close out the month. Models hints at another significant storm March 26-28 east of New Zealand that could deliver surf to near the summer average during the first week of April.

East Shores: Small surf to start but coming up to average by the weekend…

Recent/Now/Next/Finally: Surf on Sunday was 1-2’ from a NE-ENE trade wind swell. It should be similar into early Thursday due to wind swell generated primarily by a subtropical surface low centered 1,100nm ENE of Hawaii. Surf should gradually rise later on Thursday as the local and upstream trade winds increase. Surf should be 1-2’+ by Friday and 1-3’ by Saturday. Surf should peak at 2-3’ on Sunday and Monday as wind swell height and period continue to rise. There are no other sources of swell through this period.

Outlook: There is moderate confidence that near average wind swell will keep 2-3’ surf through the end of March and into early April. A powerful mid-latitude cyclone NNW of Hawaii on Mar 25 could bring some North wrap peaking Mar 27 at no larger than 3’ of surf.

The next full SNN Big Picture will be issued on Sunday, Mar 24.

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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