About Collaborative Surf

21 May 2013 01:00:00 GMT

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

Collaborative Surf Table

21 May 2013 01:00:00 GMT

FORECAST DATE	SWL HGT	DMNT DIR	DMNT PD	H 1/3	H 1/10	HGT TEND	PROB	WIND SPD	WIND DIR	SPD TEND
1PM 05/20	5	N	8	2	4	UP		4-6	VRB	SAME
1PM 05/20	6	S	17	10	14	SAME		4-6	VRB	SAME
TUE 05/21	4	NNW	9	3	5	SAME	MED	4-6	VRB	SAME
	5	S	15	8	10	DOWN	HIGH
	2	WNW	20	4	6	UP	LOW
WED 05/22	6	WNW	17	10	14	UP	HIGH	4-6	VRB	SAME
	3	N	9	2	4	DOWN	LOW
	4	S	14	6	8	DOWN	LOW
THU 05/23	5	WNW	14	8	10	DOWN	HIGH	7-10	E	UP
THU 05/23	3	SSW	17	4	6	UP	LOW	7-10	E	UP
FRI 05/24	3	WNW	12	3	5	DOWN	LOW	9-13	E	UP
FRI 05/24	3	S	14	4	6	DOWN	LOW	9-13	E	UP
SAT 05/25	2	NW	10	2	4	DOWN	LOW	13-19	E	UP
	6	ENE	8	2	4	UP	LOW
	2	S	14	2	4	SAME	LOW

Collaborative Surf Table Legend

21 May 2013 01:00:00 GMT

LEGEND:

SWL HGT	OPEN OCEAN SWELL HEIGHT MEASURED FROM TROUGH TO CREST IN FEET LOCATED 20 NAUTICAL MILES OFFSHORE
DMNT DIR	DOMINANT DIRECTION TYPICALLY +/-10 DEGREES IN 16 COMPASS POINTS
DMNT PD	DOMINANT PERIOD IN SECONDS
H1/3	SIGNIFICANT WAVE HEIGHT IN THE SURF ZONE
H1/10	AVERAGE HEIGHT OF THE HIGHEST ONE-TENTH WAVES IN THE SURF ZONE
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 LOCATED 20 NAUTICAL MILES OFFSHORE
WIND DIR	WIND DIRECTION IN 16 COMPASS POINTS
SPD TEND	WIND SPEED TENDENCY (VALID VALUES: UP/DOWN/SAME)

Disclaimer

21 May 2013 01:00:00 GMT

Collaborative Surf Discussion

21 May 2013 01:00:00 GMT

SURF HEIGHTS WILL VARY BETWEEN DIFFERENT BEACHES AND AT THE SAME BEACH AT DIFFERENT BREAK AREAS. DISCUSSION: Summary: out of season WNW mid week as southerly swell slowly tapers down. Detailed: mid Monday on northern shores has small, short-period breakers from 345-360 degrees. Similar surf is likely for Tuesday. A weak surface low pressure formed north of Hawaii over the weekend of 5/18-19. On the north side beyond 600 nm, strong to near gales aimed at targets slightly west of Oahu. Another weak low on Sunday formed about 1000 nm away with a short-lived fetch of similar winds aimed near to west of Oahu. The combination should keep small, short-period surf Tuesday from 345-350 degrees. The episode should drop on Wednesday and fade of Thursday. Further west, last Friday into Saturday, a low pressure deepened to 972 mb, much lower than normal for the season, in an area about 2400 nm away from Hawaii, well east of the Kuril Islands. There was about a day of severe gale to storm-force winds over the 300-310 degree band with seas growing above 30 feet. The low pressure occluded on Saturday as the girth of the circulation increased, widening the fetch for the latter stages mid Saturday into late Sunday, as the winds steadily weakened. The low center drifted NNE and should fade out on Tuesday north of the Aleutians. Similar sources during March and April 2013 were under estimated by the Wave Watch III model. Thus this forecast has nosed the numbers up to suggest marginally high surf for the peak of the episode on Wednesday. Long period forerunners are due in late Tuesday afternoon, with the peak of the episode from sunrise to noon Wednesday from 300-310 degrees. Heights should lower to moderate levels on Thursday and drop to small heights for Friday from 300-315 degrees. Tiny to small leftovers are possible on Saturday. Mid Monday on eastern shores has near nil energy from within 45-90 degrees. Exposures to NNW to N have small waves as described above with a similar trend. See the latest NWS state weather forecast discussion for an explanation of the governing weather features around Hawaii, maintaining the light wind pattern. Trades are modelled to slowly build later in the week. Since the upstream trades to the E to NE of Hawaii get a head start midweek, when the trades reach the moderate to fresh mark locally on Saturday, the surf should jump up quickly to small levels from 060-090 degrees. Mid Monday on southern shores has high surf from 170-200 degrees with 12-22 second intervals associated with the overlapping of various sources. Heights are expected to slowly trend down Tuesday. The long wave pattern in the austral mid latitude jet stream centered on 150°W 5/9-14 had numerous reinforcements in the form of short-wave troughs merging from the west. At the surface, various features provided unique sources for waves in Hawaii, and due to the different timing and distance from Hawaii, and the fact that dispersion spreads the swell trains over a vast area during the over 3500 nm travel to Hawaii, the net result was an overlapping of episodes, making for much more consistent arrival pace of sets than normal for south swells. There were two primary types of Hawaii surf-producing, surface weather features. These were occluded, nearly stationary low pressure cells and fast-moving fronts associated with jet level short waves. The occluded low pressure cells formed nearly directly below the jet level long wave trough. These features rested near 60s within 150-170°W with central pressures below 940 mb off an on during this spell. Storm- to hurricane-force winds occurred on the west side of these lows. The fetches had long durations but short fetches for the most extreme winds, since the features were fairly compact and nearly stationary. These sources added long-period energy from 170-190 degrees for Hawaii. Such sources began to arrive in Hawaii on Saturday 5/18 and continue 5/20. The last in this series of occluded low pressure sources occurred on 00Z 5/15 - 00Z 5/16 near 155°W, dropping to 934 mb 12Z 5/15 near 60s, 155°W. Long period swell from this source is filling in on Monday 5/20 and should peak on Tuesday 5/21, making for high surf out of 170-190 degrees. The second type of surface weather feature was associated with gales to storm-force winds behind fronts, which were driven to the NE by short-waves merging into the long wave jet pattern. These systems had long, captured fetches, best aimed at targets SE of Hawaii. Each grew seas up to 40 feet. Each source started S to SE of New Zealand, and had about a day with the fetch aimed straight at Hawaii centered on 190 degrees. Thus, these sources arrived with dominant energy from 190, and slowly backed on the compass toward 180 degrees as angular spreading added more 170-190 degree energy. One such frontal pattern occurred 18Z 5/13 - 00 z 5/16, with the head of the fetch reaching to about 4000 nm away from Hawaii. Energy from this source filled in locally Sunday night 5/19, with the pacioos/cdip barbers PT near shore buoy showing its signature of 16-22 second energy centered on 190 degrees on Monday 5/20 in the morning. Going into Tuesday 5/21, the angular spreading aspect from this source should add with the southerly component of the occluded source, centering the dominant energy near 175-180 degrees. Surf is expected to drop to marginally high levels by Wednesday and fall to moderate heights on Thursday. The austral long wave pattern began to weaken 5/15 as it shifted east. A more zonal jet stream set up between the longitudes of New Zealand to French Polynesia, with short-waves moving east along 60s, steering surface low pressures with about a 2 day spacing. The first one occurred 5/16-17, with the short-lived, compact area of storm-force winds nearly 4500 nm away. Such a source should make for small to occasionally moderate, long-period surf locally. This episode is expected to have forerunners late Wednesday, and hold with top sets to moderate on Thursday into Friday from 180-195 degrees. Since it is overlapping the previous episode, it should have slightly more size and consistency that would be expected from the single source alone. Into the long range, the next surface low pressure was even more compact as it passed SE of New Zealand near 60s 5/18-19. This could make for a small, long-period episode picking up 5/27 from 185-200 degrees, lasting a couple of days. In the northern hemisphere, models show a weak low pressure near the dateline just south of the Aleutians 5/23-25, that could make for tiny to small, short-period NNW surf locally within 5/28-30. Easterly windswell is expected to build to moderate levels by 5/26 and hold a few days under moderate to fresh trades locally. Long range forecasts are subject to major revisions. This collaborative forecast will resume on Wednesday, May 22. This forecast was produced through the collaborative efforts of NWS and NCDDC. Please send suggestions to w-hfo.webmaster@noaa.gov or call the Warning Coordination Meteorologist at 808-973-5275. Additional resources: see /in lowercase/ http://www.prh.noaa.gov/hnl/pages/marine.php.

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21 May 2013 01:00:00 GMT

NWS FORECASTER AND NCDDC PAT CALDWELL