GREENTEA HI 5.21 728X90

PAT CALDWELL

SwellCaldWell Update 3PM Friday, May 14, 2021

DATE

SWELL

HGT

SWELL

DIR

SWELL

PER

SURF

H1/3

SURF

H1/10

TREND

PROB

WIND

SPD

WIND

DIR

TREND

1 PM

5

NE

6

1

3

SAME

12-17

NE

SAME

05/14

3

S

15

5

7

SAME

 

 

 

 

SAT

5

NE

6

1

3

SAME

MED

12-18

NE

SAME

05/15

3

S

15

5

7

SAME

MED

 

 

 

SUN

6

ENE

7

2

4

UP

LOW

15-20

ENE

UP

05/16

2

S

13

3

5

DOWN

LOW

 

 

 

MON

3

NNW

12

4

6

UP

LOW

17-21

ENE

UP

05/17

7

ENE

7

3

5

UP

LOW

 

 

 

 

2

S

12

2

4

DOWN

LOW

 

 

 

TUE

3

NNW

11

4

6

DOWN

LOW

17-21

ENE

SAME

05/18

7

ENE

7

3

5

SAME

LOW

WED

2

WNW

17

3

5

UP

LOW

17-21

E

SAME

05/19

7

ENE

7

3

5

SAME

LOW

 

 

 


Table Definitions given after Discussion

Summary

Town topping heights for the weekend with Country near average next week.

Discussion

Midday Friday 5/14 on N exposures has breakers at a seasonal minimum. Near nil surf should hold on Saturday.

 

On this day, 5/14, in the historical H1/10 visual surf observation Goddard-Caldwell database (starting 9/1968) for the north shore of Oahu, the average is 2.6 Hs, (~5’ peak face) and the largest surf on this date was 7 Hs (~14’ peak face top spots) in 1975.

 

The north Pacific took a breather 5/9-11 and should lead to near nil surf conditions for the north shores this weekend 5/15-16. Don’t have a cow now, it ain’t the summer doldrums just quite yet.

 

A gale low formed 5/12 over the western-central Aleutians. The low center moved slowly ENE with the center in the Bering Sea east of the Date Line 5/14. ASCAT satellite showed a long fetch of near gales over the 325-335 degree band nosing closest to Hawaii about 1600 nm out 5/13. The ocean surface winds became more zonal (west to east) north of 40N to the Aleutians 5/14, aiming swell well NE of Hawaii.

 

Surf should rise from 320-340 degrees to near the May average on Monday 5/17. It will likely peak late Monday. The event should slowly trend down 5/18 near average and drop to tiny/small 5/19, when a new WNW is due.

 

A new low has formed east of northern Japan 5/14. Models show it developing to storm-force on 5/15 as it approaches 40N, 170E, or about 2000 nm out. The prognosis shows a narrow, short fetch, which lowers surf potential. The system is predicted to weaken sharply 5/16-17 as it reaches the Date Line.

 

Low, long-period energy from 305-310 degrees is expected to fill in Wednesday 5/19. The event should peak near or a notch below the May average in the PM. This event should keep tiny to small surf locally from 305-320 degrees 5/20-21.

 

Midday Friday 5/14 on the east side has breakers out of the trade wind belt of 40-90 degrees near an east side minimum. Low conditions should hold on Saturday.

 

An upper-level trough NNE of Hawaii 5/11 formed into a stationary cut-off low 5/12-14. Models keep it to the immediate ENE of Hawaii into Monday. This feature has placed gentle trades over a large area upstream of Hawaii to the E to NE. This should keep surf well below average for the weekend.

 

Latest model output suggests the upper level low to move east and weaken 5/17-18, which should allow an increase in local trade wind speeds and an uptick in breakers from wind swell. Heights should build to near the average late 5/17 and hold into midweek from 50-80 degrees.

 

Mid Friday 5/14 on southern shores has breakers from 175-200 degrees a notch over the summer average. Similar surf is predicted for Saturday.

 

On this day, 5/14, 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 7 Hs (~14’ peak face) in 1975. Holy guacamole, north shore had the peak day record 5/14 also in 1975 and the same size too! Bet there was some schitzophrenia blues that day!

 

We’re leading into the tail-end of overlapping events 5/14. There was an active pattern from S to SE of New Zealand to S to SE of French Polynesia 5/4-8.

 

The first portion of the overlapping events was from a zonal fetch S to SE of NZ aiming highest at the Americas 5/4-6. The fetch was long and wide, and seas grew above 30 feet. It was enough to knock us up into action thanks to angular spreading. Long-period swell from 185-200 degrees picked up locally 5/11 PM and grew just above average by 5/12 midday. The event held through Thursday 5/13. A reinforcement from 175-190 degrees is filling in 5/14.

 

The second portion formed as the low-pressure pattern SE of NZ took on a more NE track 5/6-7 at the eastern edge of the Hawaii swell window (near 160W). The low deepened just east of the Hawaii swell window 5/7-8. Severe gales aimed high seas just east of Hawaii.

 

NOAA southern buoy 51002 shows 5/14 to midday has registered the 15-17 second wave period bands from this source on the rise. This reinforcement should keep surf about the same on Saturday with the direction favoring 175-185 degrees. The event should fall below average Sunday. Background conditions are expected by Monday and holding at low-end, south-side levels 5/18-19.

 

Into the long range, the north Pacific jet is shifting northward but models still show potential for one or a few more near average, short-lived events before summer doldrums kick in. Nothing specific is seen at the moment beyond tiny from NW to NNW for the weekend of 5/22.

 

East side should slowly trend down to near the average 5/20-22 under E trades.

 

But what about the south side, let’s see what Wooly Worm is up to. Looks like a pau hana pa’ina in the backyard. Nice calypso music, what’s Wooly doing there? Ahh the limbo, how low can you go. That’s not a good sign for south swell 5/20-22. Ho, the bugga won the prize, $25 dollar gift certificate to the Garden Café– some choim herbivore grinds. Maybe that 25 is a clue. Could be around 5/25 that south side climbs back out of limbo!

 

The next SwellCaldWell forecast will be issued Monday, May 17.

Note, update March 4 for February surf observation data for the Climate Tidbit below.


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 March 4 to include February surf observations: What about this season (2020-21) Sep-Feb? How many days in each size category?

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

2020/21 LM   59     42     30        13          2       45      this season Sep to Feb

Average           50     50     40        14          4       58       All years (Sep-Feb)

 

We are running well below for 8-12 Hs category, but close for the extra-large (13-19 Hs).   Giant (20+) categories is also below average (12/2/2020=20 Hs and 1/16/2021=30 Hs; 3 days notch under giant at 18 Hs, 12/31, 1/14, and 2/13). So overall for the number of days of the big stuff (high to giant, 8+) , yes, La Nina moderate has made fewer days this season (2020/21) 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,

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’). H1/100th
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.

 

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