COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU
NWS/NCDDC HONOLULU HI
259 PM HST WED OCT 17 2018
This collaborative forecast will be updated Monday through Friday at 300 PM when Pat Caldwell is available.
FORECAST
DATE | SWL
HGT | DMNT
DIR | DMNT
PD | H
1/3 | H
1/10 | HGT
TEND |
PROB | WIND
SPD | WIND
DIR | SPD
TEND |
1PM
10/17 | 8 | NNW | 15 | 15 | 20 | DOWN | | 13-19 | ENE | SAME |
| 5 | ENE | 7 | 2 | 4 | SAME | |
| 3 | SSW | 13 | 4 | 6 | SAME | |
THU
10/18 | 7 | NNW | 12 | 10 | 15 | DOWN | MED | 11-16 | E | DOWN |
| 5 | ENE | 7 | 2 | 4 | DOWN | MED |
| 2 | SSW | 12 | 3 | 4 | DOWN | LOW |
| 1 | SSW | 17 | 2 | 4 | UP | LOW |
FRI
10/19 | 6 | NNW | 10 | 8 | 10 | UP | LOW | 7-10 | ENE | SAME |
| 2 | SSW | 16 | 3 | 5 | SAME | LOW |
| 2 | SSW | 22 | 4 | 7 | UP | LOW |
SAT
10/20 | 5 | N | 10 | 6 | 8 | DOWN | LOW | 9-13 | NE | UP |
| 5 | SSW | 18 | 10 | 14 | UP | LOW |
SUN
10/21 | 4 | N | 10 | 4 | 6 | DOWN | LOW | 11-16 | ENE | UP |
| 5 | SSW | 17 | 10 | 14 | SAME | LOW |
MON
10/22 | 3 | NNW | 11 | 4 | 6 | UP | LOW | 11-16 | E | SAME |
| 5 | SSW | 16 | 8 | 12 | DOWN | LOW |
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) |
Oahu Surf Climatology
Surf heights will vary between different beaches and at the same beach at different break areas.
DISCUSSION: SUMMARY... More common October surf in the latter part of the week for northern shores while uncommonly high surf arrives for southern exposures.
DETAILED:. Mid Wednesday on northern shores has breakers from 320-345 degrees at levels well above the October average-- more like the January average. Heights are expected to trend down though remain above the October average on Thursday.
A broad low pressure system to 967 mb strengthened as it moved east along 50N near the Date Line 10/13-14 and occluded 10/14 north of Hawaii. It slowly moved NNE into the eastern Bering Sea 10/15-17.
NOAA NW Hawaii buoys 51001 and 51101 mid day 10/17 show the long- period phase of 16-19s wave energy has ended. The dominant wave period is shifting to moderate wave periods of 12-15s.
The large circulation 10/14-17 maintained near gales from near the Aleutians west of the Date Line to near 40N north of Hawaii. 10/17 morning ASCAT shows the system has weakened substantially and the fetch area is no longer aiming at Hawaii. Surf from the tail of the fetch through 10/16 PM should keep shorter period surf into Sunday from 330-360 degrees.
A low pressure formed along the front associated with the above low pressure. This compact near gale near 40N, 170W 10/16 is tracking east 10/17 NNW of Hawaii. The strong to near gale breezes are expected to reach about 500 nm away north of Hawaii early Thursday with the system east of the Hawaii swell window late Thursday 10/18.
Shorter-period surf from 330-360 should override the remote shorter-period surf of similar direction building Friday to near the October average in the PM. This event should hold into Saturday then slowly drop into Sunday.
Another near gale in the models near the Date Line at 40N 10/18-19 could keep small surf from 320-340 degrees Monday. The north Pacific jet stream 10/19-22 is modelled to go zonal, or more west- to-east, which is usually associated with below average surf locally.
Mid Wednesday on eastern shores has breakers from 40-70 degrees at levels below the trade windswell average. Heights are expected to remain low from this direction on Thursday.
More northerly exposures of the east side should remain active through the weekend aforementioned.
Though trades are in the local forecast, the upstream fetch is short, so breakers from trade wind waves should remain low through the period. The the latest NWS State Forecast Discussion for more details on the trend in the local winds.
Mid Wednesday on southern shores has breakers from 180-220 degrees above the summer average. Heights are expected to drop on Thursday.
The characteristics of the southerly swell in the NOAA and PacIOOS buoys 10/17 are difficult to distinguish given the active NNW swell. Surf cams show surf has not changed much on 10/17 from 10/16. Given every day of October has been at the summer average or greater, there has been a lot of austal extra-tropical low pressures in the Hawaii swell window over the last two weeks. With the long travel, such active patterns are slow to fade away-- a quasi-explanation of why the surf held on into 10/17. Thursday should see a minimum before another round of above average surf arrives for the weekend.
A gale in the Tasman Sea and east of New Zealand 10/11-12 pushed into the subtropics to near 3500 nm away. Forerunners from this source are due on Thursday and should be filled in near the summer average on Friday from 190-220 degrees.
The south Pacific, mid-latitude jet stream set up a sharp ridge over the Tasman Sea and a sharp trough east of New Zealand 10/12-14. A large area of low pressure near 65S to the SE of New Zealand moved slowly east as severe gales to storm-force winds nosed into the Hawaii swell window to the S of New Zealand early 10/12 then to E of New Zealand by early 10/13. Seas over 30 feet covered an area from 170E-170W, 45-65S by early 10/13. The long, wide fetch had direct aim at Hawaii. The pattern remained fairly stationary into 10/15 with mostly gales over this exceptionally large wave generation region. This should make for a long-lived, well-above average event locally.
The PacIOOS/CDIP American Samoa buoy showed the start of the 18-22s long-wave period energy late 10/15 with a slow build into late 10/16. This suggests a similar slow build-up locally starting early Friday with inconsistent long-period sets from 190-200 degrees. Heights could climb above average on the sets Friday PM.
The event should be filled in by Saturday from 180-200 degrees and continue to build well above average in the PM. The event should remain well above average into Monday from the same direction.
Into the long range, given the large source area, the event should change slowly 10/23 with a downward trend into 10/24 as a new event builds. The source for the next one can be seen in the ASCAT satellite ocean surface winds 10/16 PM and 10/17 AM with a large, wide fetch of severe gales aimed at Hawaii to the SE of New Zealand. Models show the nose of the gales pushing to the subtropics by 10/19 as the associated low pressure moves east near 55S. This should make for another well-above average event locally. It should be filled in by 10/24 PM and remain elevated from 180-200 degrees into 10/26. Models suggest the low occluding near 150W south of French Polynesia 10/20, with a few more days of wave generation over the 175-185 degree band aimed at Hawaii. This would keep above average surf into the last week of October.
In the northern hemisphere, mostly below average events are suggested from NW to NNW 10/23-25. Models have been hinting at a tropical low pressure becoming extratropical NNW of Hawaii 10/23. This could trend the surf up locally 10/26-27 from NNW to N.
East side is expected to remain below average 10/23-25.
Long range forecasts are subject to high uncertainty.
This collaborative forecast will resume on Friday, October 19.
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
NWS Forecaster and NCEI Pat Caldwell
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