New Swell Classification Guidelines (Winter)
Significant: Swell 8 ft @ 14 secs or greater (11+ ft faces) for 8+ hours (greater than double overhead)
Advanced: Swell and period combination capable of generating faces 1.5 times overhead to double overhead (7-10 ft)
Intermediate: Swell and period combination generating faces at head high to 1.5 times overhead (4-7 ft)
Impulse/Windswell: Swell and period combination generating faces up to head high (1-4 ft) or anything with a period less than 11 secs.
On Thursday (9/18) North/Central California continued small with mainly just background southern hemi swell and bare minimal northwest windswell intermixed. Southern California was getting a little more of the southern hemi swell, but not much. Hawaii's North Shore still had some small northerly swell on the North Shore. The South Shore had no real swell. Nothing on the East Shore either.
For Central California south swell is expected to be starting fade on Friday, and smaller still on saturday and Sunday while northwest windswell from the dateline region moves in late Friday peaking Saturday. But even this to only be in the chest high range, maybe a tad higher with luck. Southern CA to southerly angled swell fading on Friday and just barely noticeable through the weekend before dissipating. No northwest swell expected to wrap-in. Minimal northern energy is forecast for the North Shore through Friday (9/19), then fading out over the weekend. No tradewind generated east windswell forecast into next week on the East Shore. The South Shore of Hawaii was inactive and expected to stay there with swell for the week.
The long-term overview has a series of tiny low pressure systems forecast for the North Pacific starting early next week, one north of Hawaii and another in the West Pacific building slightly while tracking east and offering minimal swell potential fro California and Hawaii perhaps by next weekend (9/27). But nothing impressive is suggested. Down south one small gale pushed east off the Northern edge of the Ross Ice Shelf earlier this week generating up to 35 ft seas, offering some background potential mainly for for California late next week. But nothing else of any real interest is on the charts. See details below...
SHORT- TERM FORECAST
Current marine weather and wave analysis plus forecast conditions for the next 72 hours
On Thursday (9/18) the North Pacific jetstream was split but not so bad, with the main flow tracking flat off Japan tracking east on the 40N latitude pushing right up to Central CA. But winds were only 90 kts, not offering any support for surface level development. Bit's and pieces of a secondary flow were tracking through the Bering Sea occasionally pushing south into the greater North Pacific. Over the next 72 hours no real change is forecast with a a generally weak split flow continuing. Beyond 72 hours much more energy is forecast building over Japan and pushing east towards the dateline by Wed (9/24), then getting redirected northeast towards the Aleutians with a weak secondary flow tracking north of it in the Bering Sea. Maybe some hope for surface level development in the far West Pacific, but the flow is far from optimal.
At the surface today a placid wind pattern was in control. A weak 992 mb low pressure system was in the Northern Gulf and mostly inland over Alaska generating 20 kt northwest winds over open water of the Gulf and of no interest. No other fetch was occurring. Over the next 72 hours high pressure is start building in the Gulf of Alaska setting up the usual pressure gradient along the California coast and generating north winds there by Sunday and on the increase into Tuesday, then fading. Short period windswell to result for Central CA. At the same time a low pressure system is to build north of Hawaii backing up in the high and puncturing it, possibly generating 35 kt winds briefly aimed at Hawaii and the US West Coast Tuesday (9/23) offering some swell potential. Also a second small low to pushing northeast off Japan tracking to the dateline with 35 kt winds briefly targeting Hawaii on Monday (9/22). But all this is still a bit away, and far from guaranteed.
North Pacific Animations: Jetstream - Surface Pressure/Wind - Sea Height - Surf Height
California Nearshore Forecast
On Thursday (9/18) weak high pressure at 1020 mbs was 6800 nmiles west of Pt Conception but doing nothing wind-wise near the coast. A light wind flow was in-play. No change is forecast through Saturday with winds less than 15 kts over the entire coast. Then on Sunday a broad 1028 mb high pressure system is to start building off Oregon setting up a new gradient and north winds building over nearshore waters Sunday (15 kts) up to 30-35 kts early Tuesday and Wednesday (9/24) initially off Pt Reyes moving up towards Cape Mendocino. But winds to remain close to the coast through Wednesday Tuesday and wrapping into Santa Barbara, making an absolute mess of things, though offering some short period windswell generation potential. Greater Southern CA to remain protected though.
On Thursday (9/18) Tropical Storm Sinlaku was located just off South Japan with winds 50 kts tracking steadily northeast. This track is to continue with gradual acceleration with the system moving into open waters of the North Pacific Saturday (9/20) with winds 40 kts. Limited odds of it developing into anything that might produce swell for US waters, but the models suggest it to get caught up in the low pressure stalled over Kamchatka, and dragged north into the Bering Sea before even reaching the dateline. Low odds for swell development.
On Thursday (9/18) a split jetstream pattern remained tracking west to east over the South Pacific with no clear cohesive flow present. The southern branch was generally flowing flat west to east down at 65S, with something that resembled a ridge over the Central South Pacific and not supportive of surface level low pressure development. Over the next 72 hours that same pattern is to generally hold but with the ridge giving way to a trough, again in the Central Pacific but with winds only 90 kts flowing through it, offering only meager fuel to support surface level low pressure development there Sat-Mon (9/22), then fading out as it moves further east. Beyond 72 hours a muddled and incoherent pattern to return for a bit, then move into a zonal (flat) flow tracking over the northern edge of the Ross Ice Shelf offering no clear cut support for low pressure development at the oceans surface.
At the oceans surface one small fading low pressure system was moving northeast after building over the Ross Ice Shelf Wednesday (9/17). this morning (Thursday AM) it was tracking more to the northeast free and clear of ice with 40 kts winds at 54S 132W generating barely 30 ft seas at 56S 135W, expected to dissipate in the evening. 29 ft seas fading are to be fading Thurs PM from 52S 125W. Limited sideband swell possibly pushing up into Southern California Fri PM (9/26) with period barely 16 secs. Over the next 72 hours a diffuse but broad low pressure system to build well southeast of New Zealand producing 35-40 kt southwest winds Saturday AM (9/20) and barely 30 ft seas at 50S 164W tracking east with 35 kts winds and 30 ft seas holding through Sunday PM (9/21) moving to 48S 138W then dissipating. Possible small swell best aimed towards California and unshadowed by Tahiti for the later half of it's life if this occurs.
Second Southeast Pacific Gale
On Tuesday AM (9/9) a gale was building in the mid Pacific at 944 mbs generating a broad fetch of 40-45 kt southwest winds at 55S 142W aimed 25 degrees east of the 192 degree path to California and getting better traction on an already rough sea (from the Southeast Pacific Gale above). By Tuesday evening (9/9) the fetch was broad but fragmented with 40 kt southwest winds generally at 53S 127W aimed 30 degrees east of the 182 degree path to California with more energy building behind and south of it. 30 ft seas were modeled at 53S 133W. On Wednesday AM (9/10) a new fetch of 40 kt west winds winds built at 56S 140W aimed 60 degrees east of the 188 degree path to CA. Seas from the previous fetch were 32 ft at 53S 122W. In the evening the fetch faded with no seas of interest remaining. This system produced some limited seas and winds in the eastern edge of the Ca swell window, offering potential for small to moderate very southerly angled swell for both North and Central CA starting Wednesday PM (9/17) for SCal.
Southern CA: Expect swell arrival starting Wednesday PM (9/17) with swell 2 ft @ 18 secs (3.5-4.0 ft). Swell to peak Thursday AM (9/18) with swell 2.6 ft @ 16-17 secs (4.0-4.5 ft faces). Swell Direction: 185-190 degrees
Northern CA: Expect swell arrival starting Thursday AM (9/18) with swell 2 ft @ 18 secs (3.5 ft). Swell to peak late Thursday/early Friday (9/19) with swell 2.6 ft @ 16 secs (4.0 ft faces). Swell Direction: 187 degrees
Small New Zealand Storm
A small storm formed under New Zealand Monday AM (9/15) with 50 kts winds over a tiny area at 60S 172E aimed due east and pushing east into Tuesday (9/16) with winds confirmed at 55 kts Monday evening at 58S 165W, then fading from 40-45 kts Tuesday AM at 57S 150W and aimed more to the north, expected to be gone by night fall. 36 ft seas were modeled over a small area Monday PM (9/15) at 60S 175W barely off the northern edge of the Ross Ice Shelf fading from 34 ft Tues AM at 58S 160W, then gone (29 ft at 56S 150W in the evening). Limited background swell possible for Hawaii starting Wed (9/24) but odds very low, and California Fri (9/26) (better odds).
Small New Zealand Storm
A small storm formed under New Zealand Monday AM (9/15) with 50 kts winds over a tiny area at 60S 172E aimed due east and pushing east into Tuesday (9/16) with winds confirmed at 55 kts Monday evening at 58S 165W, then fading from 40-45 kts Tuesday AM at 57S 150W and aimed more to the north, expected to be gone by night fall. 36 ft seas were modeled over a small area Monday PM (9/15) at 60S 175W barely off the northern edge of the Ross Ice Shelf fading from 34 ft Tues AM at 58S 160W, then gone (29 ft at 56S 150W in the evening). Limited background swell possible for Hawaii starting Wed (9/24) and California Fri (9/26).
South Pacific Animations: Jetstream - Surface Pressure/Wind - Sea Height - Surf Height
Marine weather and forecast conditions 3-10 days into the future
Beyond 72 hours a broader low pressure system is to build over Kamchatka Wednesday 99/240 making zero headway and just swinging up into the Bering Sea and offering no potential while high pressure again takes root in the Gulf of Alaska, shutting down production there and deflecting any eastward moving low pressure system up into he Eastern Bering Sea. Pretty quiet.
MJO/ENSO Update: As of Thursday (9/18) the Madden Julian Oscillation (MJO) continued begrudgingly giving way to the Active phase. The Daily SOI index had momentarily jump tot 13.73. The 30 day average was up a bit to 16.39 and the 90 day average was up to 5.80. This is not longer looking even neutral, but is more symptomatic of La Nina. This active phase of the MJO is expected to push all those indices down, but we'll see. Winds at at the surface and the 850 mb level (approx 1000 ft up), indicated east winds still holding on but isolated over the far Eastern Pacific mainly off Central America. The models suggest it's to slowly fade out and be gone by Thursday (9/24). Today the Active Phase was building over the Philippines expected pushing to the dateline by 9/22 then holding there while slowly fading through 10/3. It is to be stronger than even recent forecasts, though still not anything other than ordinary. It's to offer moderate support for fueling the development of North Pacific storms through the start of October.
Beyond 72 hrs a series of small but reasonably strong storms are to quickly sink southeast from under New Zealand crashing into the Ross Ice Shelf Sun-Wed (9/24) with 55 kt winds and up to 40 ft seas, but all fetch to be aimed either due east or more-so to the southeast, severely limiting the odds for swell to migrate north, assuming they form at all. The jetstream to be in control of this southward push. Low odds for any swell to result.
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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