PAT CALDWELL

SwellCaldWell Update 3PM Wednesday, July 28, 2021

DATE	SWELL HGT	SWELL DIR	SWELL PER	SURF H1/3	SURF H1/10	TREND	PROB	WIND SPD	WIND DIR	TREND
1 PM	5	ENE	6	1	3	SAME		10-15	ENE	SAME
07/28	1	S	15	1	2	SAME
THU	5	ENE	6	1	3	SAME	LOW	10-15	ENE	SAME
07/29	1	S	15	1	2	SAME	LOW
FRI	5	ENE	6	1	3	SAME	LOW	11-16	ENE	SAME
07/30	1	S	16	1	2	SAME	LOW
SAT	6	ENE	6	2	3	UP	LOW	13-19	ENE	UP
07/31	1.5	S	15	2	4	UP	LOW
SUN	7	ENE	7	3	5	UP	LOW	17-21	ENE	SAME
08/01	1.5	S	14	2	4	SAME	LOW
MON	7	ENE	8	4	6	UP	LOW	17-21	ENE	UP
08/02	1.5	S	4	2	4	SAME	LOW

Table Definitions given after Discussion

Summary.

Low mode.

Discussion

Midday Wednesday 7/28 on northern shores has summer conditions of near nil. The same expected for Thursday.

On this day, 7/28, in the historical H1/10 visual surf observation Goddard-Caldwell database (starting 9/1968) for the north shore of Oahu, the average is <1 Hs, (<2’ peak face) and the largest surf on this date was 4 Hs (~9’ peak face top spots) in 1987.

No sources for surf beyond tiny are expected this period from WNW to NE.

Midday Wednesday 7/28 on the east side has below average breakers. Low conditions should hold on Thursday.

The local and upstream (to E to NE out 800 nm) trades 7/26-28 are mostly moderate (11-16 knots), which is not enough magnitude for wind swell breakers beyond tiny to small. This pattern should hold into early Friday as a new trade event fills in over and upstream. This should trend surf Saturday into Sunday towards the average, and above average by Monday 8/2 from 60-90 degrees.

Midday Wednesday 7/28 on southern shores has seasonal minimal surf. Low surf is predicted for Thursday.

On this day, 7/28, in the historical H1/10 visual surf observation Goddard-Caldwell database (starting 1972) for the south shore of Oahu, the average is 2.8 Hs, (~6’ peak face) and the largest surf on this date was 8 Hs (~16’ peak face) in 1994 from S under 20 knot E winds.

NOAA southern buoys and the PacIOOS/CDIP nearshore south exposure buoys 7/28 show a slither of 12-16 second energy from the south. There were a string of fast-moving, compact low-pressure systems moving east along 55S to the S to SE of New Zealand 7/21-24. Highest seas were aimed at the Americas. Angular spreading should make for low, long-period surf out of 170-190 degrees locally off and on within 7/29-8/1.

The austral midlatitude jet stream 7/25 began to build a large ridge near New Zealand (bad for Hawaii surf) and a massive trough SE of French Polynesia (good for the Americas). The latter resulted in a series of surface lows with gales to storm-force winds aimed well E of Hawaii. Low odds for any surf locally beyond background from 160-180 degrees 8/1-2.

Into the long range, let’s see what Wooly Worm is up to. There he is in the backyard, what’s that furry thing, looks like a cat-apilla got his tongue. That can mean only one thing—nothing to say. Not good news for surf with models suggesting only short-period breakers from ENE to E (north Pacific trades) and ESE to SE (south Pacific trades).

The next SwellCaldWell forecast will be issued Friday, July 30.

Mahalo Surf News Network for helping advertise my daughter and her Circadium Circus school classmates’ show “ASTRA”, but note that web site is a little misleading, it says for Saturday July 17. But the show is still upcoming this weekend, 7/31 and 8/1, so click on Select a Date, and choose time/date (2 shows each day Saturday and Sunday). Mahalo for support.

The next SwellCaldWell forecast will be issued Wednesday, July 28.

June 2021 stats added to historic stats (7/4/2021) below

Climate Fun 1.

Monthly Stats

North Shore Oahu (1968-present):

May: nsstat05

June: nsstat06

South Shore Oahu (1972-present):

May: ssstat05

June: ssstat06

Wind (1988-present, PC’s best guess):

May: wwstat05

June: wwstat06

Seasonal Stats

North Shore Oahu, September to May: nmstat09_05

South Shore so far this season (March to June) compared to earlier: smstat03_06

Climate Fun 2. Relative to Country Season 2020-21

Climate Tidbit- How does N Shore fair under moderate La Nina: history vs this year

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 1/3^rd 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,
H1/3 to H1/10	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’). H1/100^th 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.