SURF N SEA BLOW OUT 2020. 728 11.30-

PAT CALDWELL

Hazards

No high surf advisory or warnings.

Forecast

NOTE: Please check with local authorities regarding beach closures.
Surf along north facing shores will be 3 to 5 feet today, lowering to 1 to 3 feet Friday.
Surf along east facing shores will be 2 to 4 feet through Friday.
Surf along south facing shores will be 2 to 4 feet today, rising to 3 to 5 feet Friday.
Surf along west facing shores will be 2 to 3 feet through Friday.

Outlook

Outlook through Thursday September 17: The current small northwest swell will gradually lower today through Friday, with very small or flat surf expected Saturday through the middle of next week.
Surf along south facing shores will hold near the summertime average today through Saturday.
East shore surf is expected to remain small and below the summertime average through the middle of next week.
A persistent small southeast swell will remain in place through the middle of next week, bringing steady small breakers into exposed shorelines.
Surf heights are forecast heights of the face, or front, of waves.
The surf forecast is based on the significant wave height, the average height of the one third largest waves, at the locations of the largest breakers.
Some waves may be more than twice as high as the significant wave height.
Expect to encounter rip currents in or near any surf zone.
The SRFHFO product will change format and be expanded to more islands on or about September 10, 2020.
More information at: https://www.
weather.
gov/hfo/statesurf2020 .

About Collaborative Surf

This collaborative forecast will be updated Monday through Friday at 300 PM when Pat Caldwell is available.

Collaborative Surf Table

FORECAST
DATE
SWL
HGT
DMNT
DIR
DMNT
PD
H
1/3
H
1/10
HGT
TEND

PROB
WIND
SPD
WIND
DIR
SPD
TEND
1PM
11/30
4NNW1368SAME7-10ENEDOWN
4NE824DOWN
TUE
12/1
4NNW1468SAMELOW4-7LVSAME
8NW211824UPLOW
WED
12/2
17NNW193848SAMELOW7-11EUP
THU
12/3
12NNW152430DOWNLOW4-7LVSAME
FRI
12/4
8NNW131216DOWNLOW13-19NEUP
SAT
12/5
8NW141216UPLOW13-19EDOWN
6ENE613SAMELOW

Collaborative Surf Table Legend

LEGEND:

SWL HGTOpen ocean swell height measured from trough to crestin feet located 20 nautical miles offshore
DMNT DIRDominant direction typically +/-10 degrees in 16 compasspoints
DMNT PDDominant period in seconds
H1/3Significant wave height in the surf zone
H1/10Average height in the highest one-tenth waves in the surfzone
HGT TENDHeight tendency of swell (valid values: UP/DOWN/SAME)
PROBProbability of occurrence (valid values: HIGH/MED/LOW)
WIND SPDOpen water wind speed measured in knots located20 nautical miles offshore
WIND DIRWind direction in 16 compass points
SPD TENDWind speed tendency (valid values: UP/DOWN/SAME)

Disclaimer Links

Compass & Swell Shadow Lines for Hawaii

Oahu Surf Climatology

Disclaimer

Surf heights will vary between different beaches and at the same beach at different break areas.

Collaborative Surf Discussion

DISCUSSION: SUMMARY.
.
.
.
Taste of winter.
DETAILED:.
Mid Monday on has breakers of 10-16 seconds from 320-350 degrees below the fall season average.
This event should hold about the same into Tuesday PM as extra-long wave periods arrive with imminent well above average surf Tuesday night.
A long-lived zonal jet stream near the Aleutians has held for about a week.
It has kept steady, below average NNW surf off and on since the holiday.
One last reinforcement is due overnight to keep similar surf on Tuesday from 320-350 degrees.
A winter-caliber low pressure system formed east of the Kuril Islands Saturday 11/28 with central pressure dropping to near 960 mb.
The system moved steadily east near 47N with peak winds to hurricane force near the center and a wide circulation of severe gales to storm-force winds stretching over a vast region.
The center crossed the Date Line Sunday PM 11/29 then continued east to 168W into 11/30 as it occluded.
When a wave-generating weather pattern travels in a similar direction at a similar speed to a growing swell, it is called captured fetch.
The high swell continues to receive wind stress from the strongest portion of the weather system, allowing continued wave height increase.
For winds severe gale to storm-force winds, it takes about 2 days over near 1000 nm in order to reach fully-developed seas, or the maximum wave heights possible of a given wind strength.
The captured fetch phenomenon allows an apparent fetch duration and length to reach this criteria.
In this case, winds over the S to W quadrant of the broad area of low pressure were the source for a captured fetch over the 310-325 degree band relative to Hawaii.
JASON altimeter measured combined seas and swell 35-40 feet within 40-45N, 170E, or about 2000 nm away from Hawaii, near 8 AM HST Sunday 11/29.
Once the system was east of the Date Line late 11/29, highest seas and swell aimed at targets just NE of Hawaii.
A JASON altimeter reading 40-44 feet was measured in the swatch aimed just NE of Hawaii north of 40N, 165W.
Models suggest swell on the great circle ray near 325 degrees rolling towards Hawaii to be within 32-36 feet in a region about 1200 nm away at 2 AM HST 11/30.
This puts the peak of the event on Wednesday.
Models show a fetch of near gales over the 310-330 degree band to nose to near 700 nm away Tuesday morning, which would add shorter period surf for Thursday.
The main source for this event is modelled to weaken sharply 12/1.
Extra-long wave periods are expected to arrive locally Tuesday PM 12/1.
Fine tuning on arrival can be made early Tuesday from the NW NOAA buoys.
Wave Watch III brings the start as early as Tuesday AM locally, but historically, the model has biased early on surf large events.
Better odds for the start of the sharp rise near or just after sundown Tuesday from 305-325 degrees.
The swell should be sufficiently filled in pre-dawn Wednesday 12/2 from 305-330 degrees coinciding with high water levels from a high astronomical tide and a local sea level positive anomaly to induce above average coastal wave wash for NW exposures.
Surf Wednesday morning 12/2 from 305-330 degrees should reach giant levels, defined by larger sets surpassing 40 feet peak face on zones of high refraction of outer reefs.
Breaker heights closer to shore are lower, about 50-75 percent less for top spots.
In general, the larger the waves, the deeper the water where they break, so the breaker zone can be one-half to one mile wide along the exposed coasts, making it hard to see the largest waves.
The event should peak mid Wednesday.
Extreme, at-shore water level changes occur under such conditions making nearshore activity exceptionally dangerous.
Heights should steadily drop Thursday into Friday though remain above average from 305-345 degrees with 12-18 second wave periods.
Heights may drop to near average late Friday as a new event arrives.
Models show the jet stream at a more common winter location within 25-45N this week.
A zonal mode is predicted for 11/2-4 with a wide fetch of lower-end gales over the 300-320 degree band moving rapidly east passing the Date Line late 12/2 and within 800 nm of Hawaii late 12/3 over more the 320-340 degree band.
This should make for above average surf building late Friday 12/4 and peaking Saturday 12/5 from a wide direction swath of 300-340 degrees of moderate periods within 12-18 seconds.
Mid Monday on has below average breakers from mostly 30-70 degrees.
Heights decrease from this direction on Tuesday.
See the latest NWS State Forecast Discussion regarding the trend in local winds and skies.
The trade wind belt to the E to NE of Hawaii is entering a quiet mode with below average surf from 50-90 degrees expected this period.
A short-lived trade wind event 12/4-5 is not expected to bring surf above small levels.
Refraction and diffraction from such extreme NW to NNW events aforementioned should make for above average breakers 12/2-3 at select exposures of the east side.
Mid Monday on has near nil breakers typical of late fall.
Similar surf is predicted for Tuesday.
No austral midlatitude sources in the Hawaii south swell window were identified last week that could bring surf much beyond the November average of near nil this week.
, swell out of the southern hemisphere should remain near nil 12/6-8.
Hints of a low Tasman from 208-220 degrees 12/9-10.
With the jet stream not too far to the N of Hawaii, a series of east-moving, nearby highs and lows are expected to make for mostly light winds with wind potential from around the compass.
The trade wind belt source should remain low 12/6-10.
Models show a low dropping below 950 mb 12/5 near 50N, 165W.
This could bring another event well above average arriving late 12/6 and peaking 12/7 from 310-340 degrees.
Long range forecasts are subject to low confidence.
The next Collaborative Forecast will be updated Wednesday, December 2.
This forecast was produced through the collaborative efforts of NWS and NCEI.
Please send suggestions to w-hfo.
webmaster@noaa.
gov or call the Warning Coordination Meteorologist at 808-973-5275.
ADDITIONAL RESOURCES: See https://www.
weather.
gov/hfo/marine

Collaborative Surf Discussion (html formatted)

DISCUSSION: SUMMARY.
.
.
.
Taste of winter.

DETAILED:.
Mid Monday on northern shores has breakers of 10-16 seconds from 320-350 degrees below the fall season average.
This event should hold about the same into Tuesday PM as extra-long wave periods arrive with imminent well above average surf Tuesday night.

A long-lived zonal jet stream near the Aleutians has held for about a week.
It has kept steady, below average NNW surf off and on since the holiday.
One last reinforcement is due overnight to keep similar surf on Tuesday from 320-350 degrees.

A winter-caliber low pressure system formed east of the Kuril Islands Saturday 11/28 with central pressure dropping to near 960 mb.
The system moved steadily east near 47N with peak winds to hurricane force near the center and a wide circulation of severe gales to storm-force winds stretching over a vast region.
The center crossed the Date Line Sunday PM 11/29 then continued east to 168W into 11/30 as it occluded.

When a wave-generating weather pattern travels in a similar direction at a similar speed to a growing swell, it is called captured fetch.
The high swell continues to receive wind stress from the strongest portion of the weather system, allowing continued wave height increase.
For winds severe gale to storm-force winds, it takes about 2 days over near 1000 nm in order to reach fully-developed seas, or the maximum wave heights possible of a given wind strength.
The captured fetch phenomenon allows an apparent fetch duration and length to reach this criteria.

In this case, winds over the S to W quadrant of the broad area of low pressure were the source for a captured fetch over the 310-325 degree band relative to Hawaii.
JASON altimeter measured combined seas and swell 35-40 feet within 40-45N, 170E, or about 2000 nm away from Hawaii, near 8 AM HST Sunday 11/29.

Once the system was east of the Date Line late 11/29, highest seas and swell aimed at targets just NE of Hawaii.
A JASON altimeter reading 40-44 feet was measured in the swatch aimed just NE of Hawaii north of 40N, 165W.
Models suggest swell on the great circle ray near 325 degrees rolling towards Hawaii to be within 32-36 feet in a region about 1200 nm away at 2 AM HST 11/30.
This puts the peak of the event on Wednesday.

Models show a fetch of near gales over the 310-330 degree band to nose to near 700 nm away Tuesday morning, which would add shorter period surf for Thursday.
The main source for this event is modelled to weaken sharply 12/1.

Extra-long wave periods are expected to arrive locally Tuesday PM 12/1.
Fine tuning on arrival can be made early Tuesday from the NW NOAA buoys.
Wave Watch III brings the start as early as Tuesday AM locally, but historically, the model has biased early on surf large events.
Better odds for the start of the sharp rise near or just after sundown Tuesday from 305-325 degrees.

The swell should be sufficiently filled in pre-dawn Wednesday 12/2 from 305-330 degrees coinciding with high water levels from a high astronomical tide and a local sea level positive anomaly to induce above average coastal wave wash for NW exposures.

Surf Wednesday morning 12/2 from 305-330 degrees should reach giant levels, defined by larger sets surpassing 40 feet peak face on zones of high refraction of outer reefs.
Breaker heights closer to shore are lower, about 50-75 percent less for top spots.
In general, the larger the waves, the deeper the water where they break, so the breaker zone can be one-half to one mile wide along the exposed coasts, making it hard to see the largest waves.
The event should peak mid Wednesday.
Extreme, at-shore water level changes occur under such conditions making nearshore activity exceptionally dangerous.

Heights should steadily drop Thursday into Friday though remain above average from 305-345 degrees with 12-18 second wave periods.
Heights may drop to near average late Friday as a new event arrives.

Models show the jet stream at a more common winter location within 25-45N this week.
A zonal mode is predicted for 11/2-4 with a wide fetch of lower-end gales over the 300-320 degree band moving rapidly east passing the Date Line late 12/2 and within 800 nm of Hawaii late 12/3 over more the 320-340 degree band.
This should make for above average surf building late Friday 12/4 and peaking Saturday 12/5 from a wide direction swath of 300-340 degrees of moderate periods within 12-18 seconds.

Mid Monday on eastern shores has below average breakers from mostly 30-70 degrees.
Heights decrease from this direction on Tuesday.

See the latest NWS State Forecast Discussion regarding the trend in local winds and skies.

The trade wind belt to the E to NE of Hawaii is entering a quiet mode with below average surf from 50-90 degrees expected this period.
A short-lived trade wind event 12/4-5 is not expected to bring surf above small levels.

Refraction and diffraction from such extreme NW to NNW events aforementioned should make for above average breakers 12/2-3 at select exposures of the east side.

Mid Monday on southern shores has near nil breakers typical of late fall.
Similar surf is predicted for Tuesday.

No austral midlatitude sources in the Hawaii south swell window were identified last week that could bring surf much beyond the November average of near nil this week.

Into the long range, swell out of the southern hemisphere should remain near nil 12/6-8.
Hints of a low Tasman from 208-220 degrees 12/9-10.

With the jet stream not too far to the N of Hawaii, a series of east-moving, nearby highs and lows are expected to make for mostly light winds with wind potential from around the compass.
The trade wind belt source should remain low 12/6-10.

Models show a low dropping below 950 mb 12/5 near 50N, 165W.
This could bring another event well above average arriving late 12/6 and peaking 12/7 from 310-340 degrees.

Long range forecasts are subject to low confidence.

The next Collaborative Forecast will be updated Wednesday, December 2.

This forecast was produced through the collaborative efforts of NWS and NCEI.
Please send suggestions to w-hfo.
webmaster@noaa.
gov or call the Warning Coordination Meteorologist at 808-973-5275.

ADDITIONAL RESOURCES: See https://www.
weather.
gov/hfo/marine

Footer

NWS Forecaster and NCEI Pat Caldwell The NWS is soliciting comments through December 20, 2020 on the discontinuation of this product.
Please see weather.
gov/media/notification/pdf2/pns20-87srd_discontinuation.
pdf for more details.

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