SURF ZONE FORECAST
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST SUN MAY 19 2013
400 AM HST SUN MAY 19 2013
HIGH SURF ADVISORY FOR SOUTH FACING SHORES
Surf along south facing shores will be 6 to 10 feet today and tonight and 4 to 8 feet Monday.
Surf along west facing shores will be 4 to 7 feet today and 3 to 5 feet Monday.
Surf along east facing shores will be 2 to 4 feet with locally higher sets through Monday.
Surf along north facing shores will be 3 to 5 feet today and 2 to 4 feet Monday.
Outlook through Saturday May 25: the current south swell will be reinforced today by another south swell with a slightly smaller magnitude. Expect this swell to diminish slowly through Monday to where the advisory can be lowered. A new northwest swell with a longer period is due in Tuesday night and peak Wednesday followed by a slow decline through the rest of the 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, in the zone of maximum refraction. 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.
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU
NWS/NCDDC HONOLULU HI
330 PM HST FRI MAY 17 2013
This collaborative forecast will be updated Monday through Friday at 330 pm when Pat Caldwell is available.
|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)|
SURF HEIGHTS WILL VARY BETWEEN DIFFERENT BEACHES AND AT THE SAME
BEACH AT DIFFERENT BREAK AREAS.
Summary: high southerly surf pattern through the period with NW pulses off and on.
Detailed: mid Friday on northern shores has flat to tiny breakers from a mix of short-period WNW, N, and refracting ENE directions. An increase is expected on Saturday.
A near gale surface low pressure formed east of the Kurils on Monday 5/13, tracked east along 45°N, approached the dateline late Tuesday, and passed the longitude of Hawaii on Thursday 5/16. Winds weakened and aimed less at Hawaii once east of the dateline. The primary surf production was from the near gale winds over the 305-320 degree beyond beyond 1500 nm away 5/14-15.
Small surf from this source is expected to slowly build on Saturday, peak Saturday night, then slowly drop into Monday as the direction favors 315-330 degree.
A severe gale has formed east of Hokkaido, Japan on 5/17. Models show the system occluding on Saturday near 40°N, 165°E as the central pressure drops to 972 mb. This is deeper than usual for the time of year. The system is then modelled to slowly track NNE reaching the dateline over the central Aleutians Monday.
The stages 5/17-18 are expected to have the strongest winds mostly severe gales over the 295-310 degree band with the head of the fetch about 2200 nm away. Long period forerunners are expected to arrive late Tuesday making small, long-period breakers. Surf should climb to moderate levels on Wednesday, peak mid day, and slowly drop to small levels by Friday 5/24 from within 300-325 degrees.
A weak surface low pressure is modelled to form within 700 nm north of Hawaii this weekend. Fresh to strong breezes on the NW side of the system could add tiny to small, short-period breakers from 340-360 degrees on Monday into Wednesday 5/20-22.
Mid Friday on eastern shores has dropping, small breakers from 50-90 degrees. Heights should lower on Saturday.
See the latest NWS state weather forecast discussion for an explanation of the upcoming spell of gentle winds. Land and sea breeze daily cycles should be the dominant wind for all coastal zones on Oahu by Sunday into Tuesday.
The trade wind belt over and within 500 nm E to NE of Hawaii is modelled to weaken 5/17-19. In turn, windward shores should drop to tiny levels for short-period energy out of 50-90 degrees on Saturday, and fall to near nil 5/19-21.
Mid Friday on southern shores has surf well into the high category from 185-200 degrees. Heights are expected to remain elevated on Saturday.
The general weather feature that best characterizes this exceptional southerly surf spell in Hawaii is a long wave trough in the austral mid latitude jet stream centered near the longitude of Hawaii to the east of New Zealand and south of French Polynesia.
Within this general pattern are a whole host of complex features, with jet stream level short-waves merging from the west on about a day spacing into the larger long wave trough. In turn, each short-wave is associated with various surface low pressure features that serve as unique sources for surf in Hawaii. The net result locally is the overlapping of episodes, making for a wide directional spread from within 175-200 degrees, and with a wide wave period band. Theses aspects will make for more consistent arrival of sets than normal Saturday through Wednesday 5/18-22.
Since each new source moved into an area of existing seas from the previous sources, wave heights more readily grew. The other important aspect is wave dispersion, which is the spreading of wave energy as a function of wave period over the large travel distance of 3500 to 5000 nm away. This means that for each unique source, the first day of swell energy locally has dominant wave periods around 20 seconds, the second day focused near 17 sec, and the third day near 14 seconds. Or more simply put, overlapping episodes, which give a more consistent arrival pattern of sets. In the table above, except for 5/18, this aspect is set to a nominal direction and period. By Sunday into Tuesday, there could be at least 4 sources of varying period and direction arriving simultaneously on any given day.
The other general aspect of the weather pattern downunder was that each new short-wave jet trough and associated surface feature were slightly more poleward, or further from Hawaii. This should mean the latter reinforcement pulses late Sunday through Wednesday should be lower the the 5/16-19 surf. None-the-less, at least marginally high surf is expected Monday to Wednesday from within 175-200 degrees.
Starting Saturday, the dominant direction is expected to lean more towards straight south. Wave watch iii suggests the dominant wave direction to remain within 180-185 degrees 5/18-22, as the spread remains over the 175-200 degree band.
Into the long range, the last in the series of storm-force surface low pressure cells tracking along 60s from SE of New Zealand to S of French Polynesia occurred 5/15-16. Seas once more grew to 40 feet, with at least a 500 nm wide area over 30 feet as the previous source 5/9-14 in this area. This last pulse was even further poleward. A moderate to near high episode is expected to build on Thursday 5/23 from 190-200 degrees, peak Thursday night, and hold around the moderate mark 5/24-25 with a downward trend. The long-lived, long wave jet trough has weakened and moved east by 5/17 as the longitudes from New Zealand to French Polynesia become more zonal at the jet level. This should lead to background surf levels locally 5/26, lasting a few days.
In the northern hemisphere, the WNW pulse of 5/22-23 should fade out by Saturday 5/25. Models suggest a compact, weak low pressure cell about 1000 nm NNW of Hawaii around 5/24, that could make a small, short-period NNW episode roughly 5/27.
Eastern shores should slowly trend up 5/23-25, though remain sub-moderate. Gentle breezes are expected to continue 5/23-24.
Long range forecasts are subject to low confidence.
This collaborative forecast will resume on Monday, May 20.
This forecast was produced through the collaborative efforts of NWS and NCDDC. Please send suggestions to email@example.com or call the Warning Coordination Meteorologist at 808-973-5275.
Additional resources: see /in lowercase/ http://www.prh.noaa.gov/hnl/pages/marine.php.
|Waimea Buoy||Kailua Buoy||Lanai Buoy||Barbers Point #2||Pauwela, Maui||Kilo Nalu||Buoy 51001||Buoy 51101||Buoy 51000||Buoy 51100||Buoy 51002||Buoy 51003||Buoy 51004|