PAT CALDWELL

Hazards

HIGH SURF ADVISORY FOR EAST FACING SHORES

Forecast

Surf along north facing shores will be 6 to 10 feet through Saturday. Surf along west facing shores will be 3 to 6 feet through Saturday. Surf along south facing shores will be 3 feet or less through Saturday. Surf along east facing shores will be 4 to 8 feet today, becoming 3 to 5 feet Saturday.

Outlook

Outlook through Friday December 21: The current northwest swell is expected to persist through Saturday. A new larger northwest swell is expected to arrive late in the day Saturday, peaking at warning levels Sunday. Another, even larger, northwest swell is expected to build late Monday or Monday night, bringing another round of warning level surf to north and west facing shores Tuesday through the middle of next week. Strong trade winds will keep advisory level surf in place along east facing shores through today. Surf should drop below the advisory level by tonight, then continue to lower over the weekend as the trades weaken. 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.

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 12/13	6	NNW	13	8	12	DOWN		22-27	NE	SAME
	9	NE	9	7	9	SAME
FRI 12/14	6	NNW	13	8	12	SAME	LOW	17-21	ENE	DOWN
	8	ENE	8	5	8	DOWN	MED
SAT 12/15	4	NNW	12	6	8	DOWN	LOW	13-19	ENE	DOWN
	4	NW	22	8	12	UP	LOW
	6	ENE	8	3	5	DOWN	LOW
SUN 12/16	13	NW	19	30	40	DOWN	LOW	11-16	E	SAME
	5	E	7	2	4	DOWN	LOW
	1	SSW	14	2	3	UP	LOW
MON 12/17	9	NNW	14	16	22	DOWN	LOW	7-10	ENE	SAME
	4	ENE	7	2	3	DOWN	LOW
	1	SSW	13	2	3	SAME	LOW
TUE 12/18	14	NW	20	34	42	UP	LOW	9-13	NE	UP
	1	S	13	2	3	DOWN	LOW

Collaborative Surf Table Legend

LEGEND:

SWL HGT	Open ocean swell height measured from trough to crestin feet located 20 nautical miles offshore
DMNT DIR	Dominant direction typically +/-10 degrees in 16 compasspoints
DMNT PD	Dominant period in seconds
H1/3	Significant wave height in the surf zone
H1/10	Average height in the highest one-tenth waves in the surfzone
HGT TEND	Height tendency of swell (valid values: UP/DOWN/SAME)
PROB	Probability of occurrence (valid values: HIGH/MED/LOW)
WIND SPD	Open water wind speed measured in knots located20 nautical miles offshore
WIND DIR	Wind direction in 16 compass points
SPD TEND	Wind speed tendency (valid values: UP/DOWN/SAME)

Disclaimer

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

Collaborative Surf Discussion

DISCUSSION: SUMMARY... Steady seasonal surf from WNW to N into Saturday morning, then ramping well above average late Saturday into Sunday. DETAILED:. Mid Thursday on has breakers from 310-345 degrees at levels near the seasonal average. Similar surf is likely for Thursday of more dominant NNW angle. A zonal jet stream across the N Pacific 12/8-13 has been steering surface low pressure systems rapidly east from the Kuril Islands to the Gulf of Alaska. This is making for back-to-back events with a local wave directional spread overlapping from WNW to N. NOAA NW Hawaii buoys 51001 and 51101 to noon Thursday 12/13 shows the dominant wave period shifted down within 11-13 seconds. This event was generated by one of the fast-moving lows south of the Aleutians 12/8-10. It is expected to fade as a new event fills in early Friday. The next low in the series was mostly marginal gale from the Kuril Islands 12/10 to east of the Date Line 12/11. As the system approached the longitude of Hawaii 12/12, it intensified as a front brought near gales towards the SE crossing 35N. This batch of seas was aimed higher NE of Hawaii, but close enough to expect a continuation of seasonal surf on Friday. It should be dominant from 330-360 degrees though lower energy added within 310-330 degrees. It should peak mid Friday and slowly drop into Saturday as a new event fills in late in the day. The next low pressure system in the series gained hurricane-force rapidly late 12/12 east of Hokkaido, Japan. The system is racing east under the zonal jet. It was a broad low pressure system with central pressure to 964 mb near 45N, 175E, or about 2000 nm away from Hawaii Thursday morning 12/13. ASCAT satellite readings Thursday morning validated the hurricane force speeds. The JASON altimeter at 2018-12-13 at 12Z showed seas to near 35 feet and by 16Z near 40 feet. These are higher than the wave model guidance. The models show the low pressure continuing a rapid pace east, which is unusually for such a broad, deep low pressure system. Usually such characteristics are associated with occluded lows that slow in track speed. Models suggest a more west to east aim of the highest swell once east of the Date Line early Friday with the system east of the Hawaii swell window by late Friday. This should reduce the surf potential for Hawaii, though proximity of the highest seas combined swell from angular spreading should bring Hawaii well above average. Extra-long wave periods of 21-25s are predicted to fill in locally toward sundown Saturday from 305-320 degrees. The event should build rapidly overnight and peak near dawn Sunday from 310-330 degrees near the giant category, meaning higher sets on outer reefs in high refraction zones to at least 40 feet. The fast track should mean a Christmas tree pattern to the swell height time series with a fast rise and fall. It should drop to marginally extra- large levels by Monday morning from 315-345 degrees and down below average by late Monday. Another fast and furious low is modelled two-days behind the above. It is expected to race from the Kurils to east of the Date Line 12/14-16. Once east of the Date Line, models show the jet stream starting to expand a trough, which should result in the surface low pressure having direct aim of the high seas towards Hawaii and bringing the fetch closer to Hawaii. This would spell even larger surf locally. It is too early for specifics on size and timing. Initial estimates are for a rapid rise early Tuesday centered from 320 degrees. This event should be longer lived than the Sunday event. Mid Thursday on has rough breakers from 40-90 degrees at levels above the trade windswell average. Heights are expected to become lower on Friday. The rambunctious trades of the past ten days continue overhead the islands 12/13. The morning ASCAT satellite pass shows that the strong breezes above Oahu do not extend far offshore. Mostly moderate to fresh trades are over the larger trade windswell source region. This should lead to a steady decline in breakers from 50-90 degrees Friday into Saturday as the local winds also trend down. Heights should fall below average by Saturday PM. Mid Thursday on has nil energy from the southern hemisphere. Diffracting and refracting windswell are affected select more easterly exposures. Similar surf is predicted for Friday. A broad area of weak low pressure in the sub-tropics NE of New Zealand 12/9-11 could bring in a smidgen of swell starting Sunday from 180-190 degrees. It could linger a few days. , more one-foot wonder days from 160-200 degrees are possible off and on next week into the holiday week from austral mid latitude low pressure systems. Such conditions result in near flat conditions for most areas with select zones of high refraction having small breakers on the sets. The winter-caliber, long-period NW event arriving locally 12/19 is expected to have a heaping helping of nearby generated short- to moderate- period swell out of 330-360 degrees by late Tuesday through Wednesday, making for less organized breakers. Well-above average conditions are predicted to hold into 12/20 from more NNW. Models suggest a shear line pushing through late Tuesday, with strong breezes from NNE after the passage, and a fairly steady veering to NE by Wednesday 12/20. Rough windswell from 0-050 degrees should trend up 12/20. Long range forecasts are subject to high uncertainty. This collaborative forecast will resume on Friday, December 14. 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 http://www.prh.noaa.gov/hnl/pages/marine.php

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NWS Forecaster and NCEI Pat Caldwell