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SwellCaldWell Update 3 PM Wednesday, October 13, 2021

DATE	SWELL HGT	SWELL DIR	SWELL PER	SURF H1/3	SURF H1/10	TREND	PROB	WIND SPD	WIND DIR	TREND
1 PM	7.5	ENE	9	6	8	DOWN		12-19	ENE	DOWN
10/13	2.3	S	14	4	6	DOWN
THU	7	ENE	9	5	7	SAME	LOW	12-19	ENE	SAME
10/14	1.8	S	13	3	5	DOWN	LOW
FRI	1.5	NNW	15	2	4	UP	LOW	12-19	ENE	DOWN
10/15	6.5	ENE	9	4	6	DOWN	LOW
	1.5	SSE	11	1	3	SAME	LOW
SAT	2	NNW	12	2	4	SAME	LOW	11-16	ENE	DOWN
10/16	5	ENE	9	3	5	DOWN	LOW
SUN	1.5	NNW	11	1	3	DOWN	LOW	10-15	ENE	DOWN
10/17	4	ENE	8	2	4	DOWN	LOW
MON	1.5	NNW	11	1	3	SAME	LOW	9-13	NE	DOWN
10/18	3	ENE	8	1	2	DOWN	LOW

Table Definitions given after Discussion

Summary.

Low mode fall season spell with east side topping heights into weekend. Looking up next week for Country.

Discussion

Midday Wednesday 10/13 on northern shores has breakers for exposures to the trade wind swell. Similar conditions are expected for Thursday.

 

On this day, 10/13, in the historical H1/10 visual surf observation Goddard-Caldwell database (starting 9/1968) for the north shore of Oahu, the average is 4.7 Hs, (9’ peak face) and the largest surf on this date was 15 Hs (30’ peak face top spots) in 1982. Fall 1982 was a rambunctious surf season (Hurricane Iwa 11/23) leading into a strong El Nino winter and choke XL to giant days.

 

If you just ate lunch and are still hungry, blame it on the nada enchilada, which is giving the same treatment to the Hawaii surf this period. The pendulum is expected to swing the other way next week.

 

A narrow fetch of gales associated with a fast-moving low shifted east along the Aleutians from Kamchatka Sunday night to the Date Line Monday night, and into western Canada Tuesday night. That was one seriously zonal jet stream situation. Strongest winds with Hawaii aim were late Sunday into Monday in the Kamchatka corner over 2500 nm away. Low odds for a bump building Friday from 320-330 degrees, then lingering through the weekend into Monday as the local direction tracks clockwise on the compass.

 

Midday Wednesday 10/13 on the east side has wind swell breakers from 50-90 degrees above the trade wind swell average. Similar surf is predicted for Thursday.

 

ASCAT satellite measured strong breezes still stretching out about 1200 nm to the E to ENE of Hawaii Tuesday night into Wednesday morning. This ensures wave periods on the high end of wind swell (8-12 seconds) into the weekend, even though the overall local breezes have already started to shift down (and really shifted down when my kite hit the wind hole and fell in the ocean, then too weak to relaunch around 11:30 off Kailua today, nice little mile-long swim, got my thruster kick well practiced). An upper-level low is enhancing the cloud/occn shower bands passing through, and making for up/down conditions. Winds should hold about the same into Friday then slowly trend down to gentle by Monday. Breakers from wind swell should fall to the trade wind swell average on Saturday 10/16 then head toward a trade wind swell minimum early next week. For the long range, models suggest local winds leaning gentle through midweek, though strong trades could flare up again leading into the weekend of 10/22.

 

Midday Wednesday 10/13 on southern shores has declining, above average, long-period swell centered from 180 degrees. Heights should drop to near average Thursday morning from 170-185 degrees and steadily fall to background by late Thursday.

 

On this day, 10/13, in the historical H1/10 visual surf observation Goddard-Caldwell database (starting 1972) for the south shore of Oahu, the average is 2.4 Hs, (~5’ peak face) and the largest surf on this date was 5 Hs (~10’ peak face) in 2003 from SSE under 25 knot ENE winds.

 

An austral midlatitude weather pattern gave the recent abundance of surf — mostly from S to SE of New Zealand. Phase Three of the pattern was due south of French Polynesia at the edge of the Hawaii swell window 10/3-5. This pulse picked up locally Tuesday 10/12 bigger than expected with still some head to bit overhead sets Wednesday morning 10/13 still with some 14-16 second energy. NOAA southern buoys show the dominant energy by midday 10/13 has shifted down to mostly 12-14 seconds. The PacIOOS/CDIP buoy is also trending down. Likely one more morning with near average surf on the bigger sets, but the event will be fading fast as the wave periods shift down toward 10-12 seconds by Friday. No other sources of southern hemispheric surf are expected this period. An event within background to average is predicted locally from 185-200 degrees 10/20-22.

 

Into the long range, let’s see what Wooly Worm is up to. Where is that bugga? Oh I hear some snoring in the backroom. He was out on a pub crawl last night. There he is sleeping on my old Kodak camera. Kodak, sorta like Kodiak, that must be the clue. Yea, models place the midlatitude cyclonic center of action SE of Kodiak going into early next week. A fast-moving severe gale starting off south of the western Aleutians late Friday 10/15 should pass the Date Line 10/16 then expand in the Gulf of Alaska to the N to NNE of Hawaii 10/17-18. Since the latter portions are expected to be closer, energy from the more remote (320-330 degrees) should fill in about the same time as the building energy from the nearby source (350-010 degrees) around 10/19 PM. It is expected to peak above the October average 10/20. Hints of a follow-up N to NNE event for the weekend of 10/23.

 

The next SwellCaldWell forecast will be issued Friday, October 15.

September 2021 stats added to historic stats below 10/1/2021

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Climate Fun 1.

Monthly Stats

North Shore Oahu (1968-present):

May: nsstat05

June: nsstat06

July: nsstat07

August: nsstat08

September: nsstat09

South Shore Oahu (1972-present):

May: ssstat05

June: ssstat06

July: ssstat07

August: ssstat08

*Picts surf forecaster validation duties Big Wednesday 8/18/21

(photos Shredsniper.com, Mike Carroll)

September: ssstat09

Wind (1988-present, PC’s best guess):

May: wwstat05

June: wwstat06

July: wwstat07

August: wwstat08

September: wwstat09

Seasonal Stats

North Shore Oahu, September to May: nmstat09_05

South Shore so far this season (March to Sept): smstat03_09

 

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Climate Fun 2.

Climate Tidbit- How does N Shore fair under moderate La Nina

*yep, as of August 2021, NOAA suggesting another La Nina winter ahead for 2021-22 season.

LA NINA MODERATE (LM) — SEPTEMBER TO MAY — 1968/69 – 2019/20

Note:

1) Year denotes year of start of season Sep-May,

eg., 1968 refers to Sep 1968 – May 1969

2) Height in Hawaii scale, H1/10th, upper end of range, Goddard-Caldwell Database

3) Climate Signal (CS):

E:El Nino, L:La Nina, S:strong, M:moderate, W:weak,

N: Neutral, (+:leans El Nino, -:leans La Nina)

Count of Days Per Season of Surf by Size Category

Year CS    3-4   5-7     8-12   13-19   20+   8+ (size category, Hawaii scale)

1970 LM     84     101        39         5        4     48 (ie, 84 days in 1970-71 were 3-4 Hs, etc.)

1975 LM     96       77        47        11         1     59

1998 LM     89       74       52        16         6     74

1999 LM     72        79       47        16         1    64

2007 LM     74       75        51        17         3     71

2011 LM      88      58        39       13         3      55

2017 LM   104       54        46         7         3      56

Average  86.7   74.0    45.9   12.1     3.0   61.0     La Nina Moderate Sep-May

Average  86.2   71.5     51.7   16.5    4.5   72.6      All years                  Sep-May

So, yes, it shows  moderate La Nina years have less than average in larger wave size categories (though 1998-99 closer to normal and above average giant)– Ma Nature hates to be boxed in– keeps you guessing.

 

*Update June 4 to include Sep-May 2020/21 season surf observations:  How many days in each size category?

Year CS           3-4  5-7   8-12    13-19    20+    8+ (Hawaii scale)

2020/21 LM   104     53     39        14          2       55      this season Sep to May

Average           87     71     51        16          4       71       All years (Sep-May)

 

Yep, historic surf obs say  La Nina moderate  is below average, and 2020/21 (La Nina Moderate) fit the expected slacker count in category of days per season of high+ (8 Hs plus) than the average over all years (seasons 1968/69 through 2019/20).

 

Helpful links,

Oahu Surf Climatology

Island Shadows

Educational outreach: Waves 101– Why Surf Varies Time/Place

Table Definitions

DATE	Represents daylight hours in zones of high refraction (biggest surf spots for given incident swell direction, period and height). First row(s) in table refers to observations from buoys (swell) and cams (breakers) made for the time when the SwellCaldWell forecast was updated. Other rows refer to forecast for spell (~30-60 min) within daylight when arrival of maximum wave energy, or active envelopes, occur. This forecast tends to bias high for safety (and easier to ride a bigger board if surf is smaller than expected, than to ride a shorter board when bigger). Even under “steady” swell, heights vary spell to spell through a day.
SWELL HGT	Deep water swell (H1/3) height (feet) corresponding to a nominal (~3 mile) location offshore of Oahu seaward of the coastal shelf for the given incident swell direction. Deep water swell height from each unique wave-generating source is obtained by summing up all energy for wave periods > 10 seconds, which removes the wind swell. H1/3 is the average of the highest 1/3rd of all waves coming in for the targeted high energy envelope spell from this defined source. Wind swell are defined for wave periods <= 10 seconds.
SWELL DIR	Deep water swell direction (from) centered on 16 point compass bands.
SWELL PER	Deep water swell period (seconds).
SURF H1/3	Breaker H1/3 (defined above) height (feet, peak face) during most active envelopes. H1/3 sets arrive about every 3 minutes with large variance.
SURF H1/10	Average of highest 1/10th of all breakers (feet, peak face) during active envelopes; H1/10 sets arrive about every 10 minutes with large variance.
PEAK FACE	Trough to crest height (feet) on shoreward side of breaker at moment and location along wave front of maximum cresting,
Ocn H1/100 Cleanup or Sneaker set	Waves arrive within a range of sizes. Surf zone enthusiasts emphasize the smaller percent of larger waves when communicating a report in an X to Y occasional Z format. The X to Y range is nominally H1/3 to H1/10. The Z, or sneaker or cleanup sets, are the H1/100, which is about 1.3 times the H1/10 (eg., H1/10=10’ gives H1/100=13’). H1/100th sets arrive on average every 90 minutes with large variance. Thus your typical 2 hour session is bound to see at least one cleanup set.
TREND	Breaker height (wind speed) tendency during daylight
WIND SPD	Wind speed (knots) for nominal coastal location on the windward side relative to prevailing large scale wind (ie, east side under trades or S or W side under konas),
WIND DIR	Wind direction (from) centered on 16 point compass bands. LV refers to light and variable.