Swell Classification Guidelines
Significant: Winter - Swell 8 ft @ 14 secs or greater (11+ ft faces) for 8+ hours (greater than double overhead).
Summer - Head high or better.
Advanced: Winter - Swell and period combination capable of generating faces 1.5 times overhead to double overhead (7-10 ft)
Summer - Chest to head high.
Intermediate/Utility Class: Winter - Swell and period combination generating faces at head high to 1.5 times overhead (4-7 ft).
Summer - Waist to chest high.
Impulse/Windswell: Winter - Swell and period combination generating faces up to head high (1-4 ft) or anything with a period less than 11 secs.
Summer - up to waist high swell. Also called 'Background' swell.
On Thursday (5/17) North and Central CA had local windswell up north that was was thigh high and blown out. In Santa Cruz southern hemi swell was producing waves to occasionally thigh to waist high and clean, but chopped outside the kelp. Southern California up north had surf that was knee to thigh high and chopped. Down south sets were head high and fairly chopped and crumbled. Hawaii's North Shore had windswell in the knee to thigh high range and clean. The South Shore had very modest residual southern hemi swell at waist high and clean. The East Shore was thigh high east tradewind generated windswell and chopped.
See QuikCASTs for the 5 day surf overview or read below for the detailed view
Up north high pressure was trying to return to the California coast Thursday (5/17) with local north winds and windswell on the upswing and expected to hold into the early weekend, then fading out. But trades and windswell in the vicinity of Hawaii were lackluster. The models suggest weak low pressure moving over the Northeast Pacific by Sunday (5/20) suppressing high pressure and local windswell relative to CA and HI. But by later Tuesday (5/22) high pressure to again move into the area strongly with north winds and windswell in effect for California and easterly trades and windswell for Hawaii too and continuing into the following weekend. Down south a smaller weather system developed in the extreme Southeast Pacific on Wed (5/9) with 38 ft seas but all aimed due east to southeast with next to no swell expected up into CA. Maybe dribbles for Southern CA at best on Fri-Sat (5/19). After that no swell producing storms developed and none are forecast for the next 7 days, though the trend starts looking a bit more positive 7 days out.
SHORT- TERM FORECAST
Current marine weather and wave analysis plus forecast conditions for the next 72 hours
Surface - On Thursday (5/17) modest high pressure at 1028 mbs was positioned just off British Columbia falling south and ridging down the US West Coast producing limited north winds at 20 kts and up to 25 kts tucked right up against the coast near Cape Mendocino and Pt Conception resulting in small but building local north windswell at exposed breaks. Weak low pressure was over Japan and extending northeast to the Eastern Aleutian Islands. Trades were weak over the Hawaiian Islands with no easterly windswell resulting. In all, pretty quiet. Over the next 72 hrs low pressure in the West Pacific is to track northeast reaching the Western Gulf by Sunday (5/20) cutting the legs off high pressure along the US West Coast with north windswell fading there. The low is to try and organize, but only producing 20 kt west winds moving into the Central Gulf and fading by early Monday. No windswell expected to be produced. Trades to remain suppressed for the Hawaiian Islands.
North Pacific Animations: Jetstream - Surface Pressure/Wind - Sea Height - Surf Height
On Thursday (5/17) Tropical Depression Aletta was tracking northwest west from a point 750 nmiles south-southwest of Cabo San Lucas Mexico with sustained winds at 30 kts expected to continue fading while turning north and then doing a full circle turning back south through Monday (5/21). Given it's minimal footprint and wind speeds, no swell production is forecast relative to California or Hawaii. Of note, the formation of this system ended a 41 day streak without tropical storm activity occurring anywhere on the planet, the longest stretch of inactivity in 70 years. See like a bit of a stretch of credibility, but an interesting tidbit just the same.
California Nearshore Forecast
On Thursday (5/17) modest high pressure at 1028 mbs was riding down the US West coast centered just off British Columbia generating 20 kt north winds over the entire CA coast and up to 25 kts near Cape Mendocino and expected to continue with 25 kt north winds pushing down to Pt Conception on Friday with chop and local north windswell on the increase. Southern CA is to remain mostly protected from this. But by Saturday (5/19) the gradient is to be fading from 25 kts off Central and North CA early fading to 20 kts late. By Sunday 15 kt north winds to be over the Central CA coast making for poor conditions and offering no windswell generation potential, with the core of the fetch tracking south to Pt Conception late. Weak low pressure is to move off Oregon on Monday (5/21) with the gradient retreating to just Pt Conception (20-25 kts) and 10 kt north winds from San Francisco northward. But by Tuesday low pressure is to be clearing out of the Gulf with a 1028 mbs high building strong off the coast with north winds on the increase over Pt Conception (30 kts late) and building solidly northward on Wednesday at 25 kts up to Cape Mendocino. Southern CA to be shadowed and in and eddy flow by Wed. Windswell on the increase all locations. The gradient is to be centered off San Francisco Thursday (5/24) with fetch extending north to Cape Mendo. Windswell on the increase with no eddy flow expected yet for Central CA, though Southern CA to remain protected.
Jet stream - On Thursday (5/17) the southern branch of the jetstream was ridging south under New Zealand then breaking up some only to reorganize and ridge hard south under the Central Pacific lifting into a weak trough off Southern Chile. No support for gale development was indicated. Over the next 72 hours ridges in the west are to join forces sweeping east across the South Pacific at 70S and continuing into Sun (5/20) with the same result. The trough off Southern Chile is to try and build northwards but is to move over land by Saturday offering no real support for gale formation. Beyond 72 hours the solid ridge in the south is to finally crash into Antarctica and start dissolving by Tuesday with a new trough building east of New Zealand and slowly easing east into Thurs (5/24). Maybe some limited support for low pressure development possible.
Surface - At the surface in the South Pacific on Thursday (5/17) a gale was trying to organize east of northern New Zealand with winds to 45 kts over a tiny area. Seas were on the increase. Otherwise high pressure at 1024 mbs was over the East Pacific and a gale was starting to impact the southern tip of Chile. No swell production was yet apparent. A tiny swell was pushing north targeting Southern CA but expected to be exceedingly small (see East Pacific Gale below). And maybe one more tiny pulse to follow that for Southern CA (see Tiny East Pacific Gale below).
Over the next 72 hours the gale east of New Zealand is to peak out Thursday PM (5/17) with 45 kt west winds over a tiny area resulting in 30 ft seas Friday AM at 39S 158W targeting Chile and Peru from a very long ways away, but mostly bypassing Hawaii to the east and then dissipating quickly. No other fetch of interest forecast for the South Pacific aimed at our forecast area.
East Pacific Gale
Another small gale formed in the Central Pacific on Tuesday PM (5/8) with 45 kt west winds developing over a tiny area and seas building. The gale built to storm status and was racing fast to the east if not almost starting to fall southeast on Wed AM (5/9) with west winds 55 kts and seas building to 34 ft at 57S 140W (188 degs CA and east of the HI swell window), getting good traction on an already well agitated ocean surface but offering only sideband energy pushing up towards the US mainland and well east of any great circle path to Hawaii. 45-50 kt west winds held into the evening with seas up to 38 ft at 57S 128W (187 degs CA), and starting to actually track southeast offering less energy pushing north. By Thurs AM (5/10) this system was effectively east of the California swell window and crashing south while dissipating with seas fading from 36 ft at 59S 117W offering best swell potential for Chile up into Peru.
Limited small sideband swell is expected arriving in Southern CA on Fri AM (5/18) with pure swell up to 1.8 ft @ 16 secs midmorning (2.9 ft faces) and inconsistent from 187 degs. Residuals to hold into Sat AM (5/19) at 2 ft @ 14-15 secs (2.5 ft) then fading out.
Tiny East Pacific Gale
Another very west-to-east oriented gale developed late Friday AM (5/11) with 40-45 kt southwest winds building in the Southeast Pacific. It was racing east with seas 28 ft at 50S 130W (188 degs SCal). 45 kt west winds held Saturday AM (5/12) with 32 ft seas at 51S 120W (181 degs CA) and racing out of the CA swell window. In the evening a small area of up to 50 kt west winds evolved pushing east with seas to 36 ft over a tiny area at 51S 103W targeting only Southern Chile and well outside the CA swell window. This system was fading Sunday at with 34 ft seas at 50S 94W targeting only Southern Chile. Some tiny south angled swell is possible for mainly Southern CA down into Mexico but mainly for points south of even there.
Expect swell arrival in Southern CA on Sunday AM (5/20) at 1.8 ft @ 16 secs (2.5 ft) from 181 degrees.
South Pacific Animations: Jetstream - Surface Pressure/Wind - Sea Height - Surf Height
Marine weather and forecast conditions 3-10 days into the future
Beyond 72 hrs high pressure is to start redeveloping off Central CA on Tuesday (5/22) reaching 1028 mbs late producing north winds at near 30 kts over Cape Mendocino and trades increasing to 15 kts over Hawaii. By Wednesday north winds to be 25+ kts along the Central and North CA coast with windswell on the increase and trades to 20 kts over Hawaii with the same result and holding at least into Thursday. More reinforcing high pressure to be building too over the dateline heading east.
Note: The Madden Julian Oscillation is a periodic weather event that tracks east along the equator circumnavigating the globe. It is characterized by either enhanced trade winds and dry weather over the part of the equatorial Pacific it is on control of or slack if not an outright reversal of trade winds and enhanced precipitation. The oscillation occurs in roughly 20-30 day cycles (Inactive for 20-30 day, then Active for 20-30 days) over any single location on the planet. During the Active Phase in the Pacific the MJO tends to support the formation of stronger and longer lasting gales resulting in enhanced potential for the formation of swell producing storms. During the Inactive Phase the jet stream tends to split resulting in high pressure and less potential for swell producing storm development. The paragraphs below analyze the state of the MJO in the Pacific and provide forecast for MJO activity.
As of Thursday (5/17) the daily Southern Oscillation Index (SOI) was down to -15.61. The 30 day average was falling at 3.90 (neutral) with the 90 day average down to 0.28.
Current wind analysis indicated modest westerly anomalies over the equator from Indonesia to north of Australia with light easterly anomalies on the dateline and then dead calm from there eastward extending into Central America. This indicates that there was no discernible Phase of the MJO in play though perhaps the Active Phase was trying to build in the extreme Eastern Indian Ocean. A week from now (5/25) weak westerly anomalies are expected over the West Pacific indicative of a building Active Phase of the MJO. The longer range models (dynamic and statistical) run on 5/16 are in agreement depicting a weak Active Phase currently over the dateline and a new Inactive Phase building over Indonesia and expected to push east over the dateline 2 weeks out. None of this suggests any real benefit to the North Pacific storm track given that summer is now moving in.
But in monitoring the migration of warm water into the equatorial East Pacific, which the existing weak MJO pattern is supporting, this become important because this possibly sets up a configuration in the ocean that is more conducive to storm development for the coming Fall of 2012. In fact warmer than normal water is already starting to accumulate off Ecuador. A pocket of blocking cold water that was under the equator south of California the bulk of the past Winter (2011-2012) has evaporated and warmer water is slowly but steadily pushing east into the vacuum (Kelvin Wave). This activity was the result of the last pulse of the Active Phase of the MJO (early April) and a continued weak MJO signal, appears to be reinforcing itself. It will be interesting to see if the weak MJO pattern continues (a early sing of some flavor of El Nino) or whether the Inactive Phase comes back to life. We are still in the Spring unpredictability barrier relative to ENSO (continues into early June), so it's difficult to predict any particular outcome until that time has passed.
A weaker MJO signal is typical for this time of year, but does not normally appear as strong and as long-lasting as what appears to be occurring now, suggesting that La Nina is disintegrating. And the horseshoe cool water pattern that has dominated the entire Pacific for the past 2 years (typical of La Nina) appears to be in steep decline (a good thing). So the next question is: Will the Active-like Phase pattern that is currently occurring continue, ultimately ushering in some flavor of El Nino, or will it stall in mid-June and leave us in limbo with just a neutral pattern in play (normal)? Either option is better than where we've been for the past 2 years (under the influence of La Nina).
See imagery in the ENSO Powertool and more details in the El Nino update.
Beyond 72 hours no swell producing fetch of interest is forecast.
Details to follow...
External Reference Material: El Nino Southern Oscillation (ENSO), Madden Julian Oscillation (MJO), Pacific Decadal Oscillation (PDO), Southern Oscillation Index (SOI), Kelvin Wave
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Surf Height-Swell Height Correlation Table