Oahu Surf Conditions
Surf along north facing shores will be 3 to 5 feet today, lowering to 1 to 3 feet Friday.
Surf along east facing shores will be 2 to 4 feet through Friday.
Surf along south facing shores will be 2 to 4 feet today, rising to 3 to 5 feet Friday.
Surf along west facing shores will be 2 to 3 feet through Friday.
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.
The SRFHFO product will change format and be expanded to more islands on or about September 10, 2020. More information at: https://www.weather.gov/hfo/statesurf2020 .
|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)|
DISCUSSION: SUMMARY....Autumn is on.
DETAILED:. Mid Wednesday on northern shores has rising surf from 330-360 degrees near to a notch above the October average. Above average surf should continue on Thursday.
A classic fall season Aleutian low pressure pattern set up north of Hawaii 9/26 and is expected to hold into 10/2. Such a pattern is associated with broad, upper-level cyclonic gyre that remains fairly stationary, and is sometimes referred to as the mother low. On the western side of the mother low, a series of upper level troughs and associated surface low pressures with trailing fronts, spaced 1-2 days apart, feed into the mother low. This series is referred to as a wave family.
Each member of the wave family starts off with a weak surface low and a SE-pushing front backed by strong to near gale winds. Once the low begins to be absorbed into the mother low, an occlusion takes place with the low pressure deepening rapidly and resulting in gales or stronger winds as the low center shifts N along the eastern edge of the mother low.
Thus, each member of the wave family makes two sources for surf in Hawaii. First are the winds behind the front, making for shorter-period NNW swell, and secondly, the stronger winds west of the occluding low pressure, which makes longer-period, more N direction swell.
The closely-spaced wave family and multiple sources of each make for abundant, overlapping swell trains arriving in Hawaii. Given the location of the present mother low, this will keep active surf in Hawaii within 330-360 degrees over a wide spread of wave periods from 10-18 seconds.
NOAA NW and NE buoys 51001 and 51000 9/30 showed the shorter-period energy from 330-350 degrees arrived first on 9/29. The longer-period, more N direction of 14-18 seconds is building 9/30 in the morning. Both short- and long-period surf are on the rise Wednesday 9/30 morning on Oahu.
The short-period phase from this source should peak midday 9/30 and steadily drop on Thursday. The longer-period, more N direction energy should peak locally Thursday morning. ASCAT satellite late 9/29 showed the associated occluded low in its dissipating stage SE of the eastern Aleutians with gale to severe gale winds over a long fetch aimed at Hawaii beyond 1500 nm away. Morning ASCAT 9/30 show winds have dropped. The longer-period phase from this source that is starting 9/30 should be long-lived, overlapping with the new sources of the next member of the wave family 10/1-3.
This new wave family member 9/30 is deepening rapidly near 40N, 160W with the head of the post-frontal near gales to within 700 nm of Hawaii over the 330-350 degree band. Given the existing seas from the first event, this allows more rapid growth of the new seas. This short-period energy is due to arrive locally Friday morning from 330-350 degrees with 10-14 second wave periods, keeping surf above average. The gales that have unfolded 9/30 about 1000 nm away should bring in the new longer period surf Friday as well, with the 14-18 second energy peaking Friday PM.
Models show the second wave family low to reach near Kodiak, Alaska late Thursday. The fetch is predicted to not aim well at Hawaii by early Thursday. At the same time, the mother Aleutian low pattern starts to weaken. This should coincide with a downward trend in locally surf Saturday 10/3 into 10/4. It should fade to seasonal background levels by 10/5.
Mid Wednesday on eastern shores has breakers from 60-90 degrees below the trade wind swell average. Surf is predicted to remain low from this direction on Thursday while more northerly exposures trend aforementioned 10/1-4.
Remnant of tropical system Lowell gave small surf to Oahu. PacIOOS/CDIP Mokapu, Oahu buoy showed the peak in the 8-10 second energy 9/29. This event is fading.
No wind swell from 60-90 degrees is expected into Saturday with a slight increase of small breakers into early next week.
Tropical system Marie in the eastern north Pacific is modelled to send low, long-period surf from 80-100 degrees starting as early as 10/5. It is too early for specifics.
Mid Wednesday on southern shores has declining breakers from 170-200 degrees near the seasonal average on the less frequent sets. The PacIOOS/CDIP Barbers buoy shows the dominant energy dipping to 12-15 seconds. This event should fade toward seasonal background on Thursday into Friday.
Gales entered the southern Tasman Sea 9/26 with the fetch pushing north to the subtropics into 9/27. The onset stage is due locally late Saturday 10/3 with the event filled in late Sunday 10/4 from 208-220 degrees. It should peak 10/5 as a larger event builds.
The Tasman low-pressure pattern shifted eastward with central pressure dropping to 945 mb near 60S, 180E by 00Z 09/28. At this time, the fetch shifted east of the New Zealand shadow. Storm-force winds aimed at Hawaii while the fetch was south of 55S, or near 5000 nm away. As the low center shifted eastward and winds behind a front pushed equatorward 9/29-30, the winds aimed at Hawaii steadily weakened. There was a narrow fetch of gales just east of New Zealand 9/29, though well less than modelled, as validated by the JASON altimeter, which showed seas under 25 feet. This event has all the ingredients to make above average surf in Hawaii, though it is not expected to be much more than the recent larger events of the past few weeks since the magnitude of the winds decreased as the fetch stretched towards Hawaii east of New Zealand.
Onset stage is due Sunday PM from 190 degrees with the event filled in late Monday.
Into the long range, the New Zealand event out of 180-200 degrees should peak 10/6 above average. It should slowly decrease to near average by 10/8.
East side could potentially be above average 10/6-8 with moderate- to long-period swell from 70-90 degrees generated by tropical system Marie. Stay tuned for details
North shores are modelled to be below the October average next week 10/6-9. A weak low pressure near the Date Line at 45N 10/3 is modelled to weaken as it tracks NE. It could give a small event locally by late 10/6, peaking 10/7 at most near the September average out of 325-345 degrees.
Long range forecasts are subject to low confidence.
The next Collaborative Forecast will be updated Friday, October 2.
This forecast was produced through the collaborative efforts of NWS and NCEI. Please send suggestions to email@example.com or call the Warning Coordination Meteorologist at 808-973-5275.
ADDITIONAL RESOURCES: See https://www.weather.gov/hfo/marine