Pat Caldwell

Hazards

HIGH SURF ADVISORY FOR SOUTH FACING SHORES

Forecast

Surf along south facing shores will be 2 to 4 feet tonight, increasing to 5 to 8 feet Wednesday afternoon and 8 to 12 feet Wednesday evening. Surf along east facing shores will be 3 to 5 feet tonight, increasing to 4 to 6 feet Wednesday. Surf along west facing shores will be 2 feet or less tonight, increasing to 4 to 6 feet Wednesday evening. Surf along north facing shores will be 5 to 8 feet through Wednesday.

Outlook

Outlook through Tuesday August 28: Choppy surf along east facing shores will gradually increase this week as trade winds strengthen. Most importantly, Hurricane Lane is forecast to pass south and southwest of the islands this week, and is expected to bring rough and extra large surf to south facing shores Thursday and Friday. Be sure to monitor forecast updates on Lane as it could bring significant impacts later this week. 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 08/20	5	E	7	2	4	SAME		13-19	E	UP
1PM 08/20								13-19	E	UP
TUE 08/21	3	NNW	13	4	6	UP	MED	17-21	E	UP
TUE 08/21	7	E	7	3	4	UP	MED	17-21	E	UP
WED 08/22	4	N	13	6	8	DOWN	MED	19-23	ENE	UP
	8	E	8	4	6	UP	LOW
	6	SE	13	10	12	UP	LOW
THU 08/23	3	N	11	4	6	DOWN	LOW	22-27	NE	UP
	10	ENE	8	6	8	UP	LOW
	12	SE	12	15	20	UP	LOW
FRI 08/24	10	E	10	8	10	DOWN	MED	22-27	E	DOWN
FRI 08/24	12	S	12	15	20	DOWN	LOW	22-27	E	DOWN
SAT 08/25	8	ENE	8	4	6	DOWN	LOW	17-21	E	DOWN
SAT 08/25	6	S	12	8	12	DOWN	LOW	17-21	E	DOWN

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:. North swell and hurricane surf. DETAILED:. Mid Monday on has near flat conditions. An increase is predicted for Tuesday. An occluded low pressure just south of the Aleutians north of Hawaii 8/17-19 had a large fetch of near gales with pockets to gales. The slow-moving low pressure pattern made for a long fetch duration over the 345-360 degree band. Surf is modelled to build Tuesday, peak Tuesday night, then slowly drop into Thursday. Mid Monday on has breakers from 70-90 degrees below the trade windswell average. An increase is expected for Tuesday. See the latest Central Pacific Hurricane Center (CPHC) statements concerning hurricane Lane. Based on the 11 AM HST 2018-08-20 CPHC official forecast intensity and track of Lane, rough surf is predicted for the eastern exposures of Oahu beginning Wednesday as heights climb above average. The official track keeps Lane south of Oahu as it tracks toward the NW to NNW Thursday into Friday. This scenario means less surf from 40-90 degrees. Stay tuned for updates from the CPHC since changes in intensity and track of Lane translates into changes to the surf forecast. Conditions are expected to trend down though remain above average Friday into Saturday. Mid Monday on has a seasonal minimum of surf. Similar low surf is predicted for Tuesday. No surf beyond tiny is predicted from the southern hemisphere this period. The 11 AM 8/20 CPHC forecast of Lane would give building surf above average Wednesday from 130-160 degrees. Rough, large, hurricane surf is predicted to hold Thursday, peak late Thursday from 140-180 degrees, and slowly decline Friday into Saturday though still above average. Disclaimers on uncertainties apply to the south shore as with the east shore aforementioned. Stay tuned to the latest updates. , gales in the Tasman Sea 8/19-20 could give low, long-period swell locally 8/27-28 from 208-220 degrees at levels below the summer average. North shores are expected to stay at summer levels 8/26-28. East side is expected to remain near to above average 8/26-28 from 50-90 degrees. Long range forecasts are subject to major revisions. This collaborative forecast will resume on Wednesday August 22 or sooner if changes occur in CPHC forecasts of Lane. 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