DISCUSSION: Summary: active fall pattern in the north Pacific bringing high surf potential for the weekend. A gale formed near the Kuril Islands on Saturday 10/12 and tracked NE to the Bering Sea by Tuesday 10/15. A wide fetch of near to low-end gales covered the 305-315 degree band for the first 36 hours, and the 315-330 degree band for the latter phase. The fetches stayed beyond 2000 nm from Hawaii, far enough away to keep surf moderate or less. The episode is expected to build locally Friday afternoon from 305-315 degrees, with surf within small to moderate by sundown. This event should favor 315-330 degrees by early Saturday as it peaks at moderate levels. Several coinciding swell episodes are expected to fill in on Saturday, making for less confidence on explicit surf size, which could approach high levels in the afternoon. The sources are both remote and nearby. Such overlapping events make for more confused breakers and near shore currents. Typhoon whipa tracked near Japan on Tuesday 10/15 as it accelerated to the NNE. The system was wider than the previous typhoons in this region this season, which makes for better odds of getting long period swell of westerly component during the onset stage of the local surf episode. Fore-runners of 20-25 seconds from 280-300 degrees could fill in on Saturday making for moderate breakers for select exposures. This direction has shadowing by Kauai and Niihau on Oahu. The post-typhoon stages of whipa pose greater surf potential. On 10/16-17, the broad system expanding in size as the track turned more eastward near Kamchatka aimed along the Aleutians. It set up a long fetch of severe gales to hurricane-force winds over the 310-325 degree band, with highest seas over 40 feet aimed north of Hawaii. With the eastward track, a capture fetch has been set up. Models show the winds slowly weakening Friday at mostly gale levels, down to near gales by Saturday. The long fetch is predicted to hold over the 315-325 degree band into Saturday. The combined effects of the angular spreading and seas aimed directly at Hawaii should make for high surf locally, with the event long-lived. The surf from this source is expected to steadily build from 310-320 degrees Sunday. It should peak Sunday night, remain marginally high Monday, then drop to moderate levels by Tuesday from 310-330 degrees. Another nearby source is expected to deliver shorter wave periods and more northerly swell direction Saturday to Tuesday, overlapping with the whipa event and making for crossed-up breakers. The north Pacific jet stream is amplifying a trough near the longitudes of Hawaii, steering a surface low pressure 10/17-18 to the SE. Ascat satellite late 10/16 showed a wide area of near gales and pockets to gales in a region about 1400 nm away. Models show the low center tracking SE 10/17-18. This should set up a captured fetch over the 330-350 degree band, nosing to within about 800 nm. Proximity leads to higher surf, since less energy is lost during travel. Surf from this source is expected to ramp up rapidly during the day on Saturday, and will be monitored for high surf potential. It will likely peak Saturday night centered from 340 degrees and decline toward moderate levels on Sunday. The sharp upper level trough that is steering the surface low pressure towards Hawaii on 10/17 is predicted to pinch off an eddy 10/18-19. This would cause the surface low pressure to stall in track speed. This feature is modelled to hover to the NNE of through the weekend then drift off to the NE on Monday. Surface winds on the west side of the low are modelled in the strong to near gale bracket about 500 nm away and should make for short-period surf from 350-010 degrees Monday into Tuesday with a decreasing trend. See the latest NWS state weather forecast discussion regarding the local weather and wind pattern associated with the nearby surface low pressure this weekend. Eastern shores should remain low from 45-90 degrees, while exposures to 000-45 degrees trend with the episodes as described above from short-period more northerly swell and refracting long-period swell around the island corner. Mid Thursday on southern shores has mostly flat conditions with small, short-period breakers on the sets at a few select spot, nominally from 140-180 degrees. More of the same is expected through the weekend. A gale low pressure to the SE of New Zealand 10/14 tracked steadily east. It could make for a short-lived, small, moderate-period swell event starting Tuesday from 180-200 degrees. Into the long range, astorm-force system in the Tasman sea 10/16-18 could give background, long-period, small breakers late next week Thursday to Saturday 10/24-26 from 208-210 degrees. In the northern hemisphere, the NW Pacific is modelled to have a more zonal pattern Saturday to Wednesday 10/19-23. Thus, small NNW to N surf is expected locally 10/24-25 after the whipa event fades 10/23. Models suggest a winter-caliber low pressure system near the dateline halfway to the Aleutians by around 10/24 that could bring surf above average locally roughly 10/26 from WNW to NW. Short-lived moderate trades are possible 10/23-24 with tiny to small breakers.the proximity of this weather feature to the NW of Hawaii late next week should drop local winds to gentle speeds with potentially some southerly component for the weekend 10/25-27, with surf remaining below average from within 45-90 degrees 10/24-26
Posted on: Sat, 19 Oct 2013 06:02:24 +0000
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