Tuesday 7 21 20 morning call

Another day of inconsistent, but really good waves on the Lahaina side yesterday (ALWAYS look at the webcam yourself for at least 5 minutes despite of what I wrote or what the picture I posted looks like). This instead is Hookipa at sunset which was already feeling the energy of the NE windswell fetch we observed in the last couple of days. This is 5.5ft 8s and very mushy.


4am significant buoy readings and discussion.
South shore
Lanai
1.7ft @ 13s from 193° (SSW)            
0.7ft @ 18s from 216° (SW)

Southerly energy down to 13s but still up to 1.7ft, so that should keep waves rolling. 0.7ft 18s on top of that is a nice surprise. I don't trust the direction that would indicate a Tasman sea swell, let's see if we can identify the source with the help of Pat Caldwell.

A pair of lows south of Tahiti at the eastern edge of the Hawaii swell windows could keep near average surf midweek into the start of the weekend. The closer low pressure was weaker, with the net result of both having about equal surf potential for Hawaii.
The closer low tracked as a marginal gale from near 55S, 170W 7/14 to 45S, 155W 7/16. The head of the fetch of gales with seas 15 to 20 feet reached about 3600 nm away within 7/16-17. It moved east of the Hawaii swell window 7/18 as seas continued to climb, but not aiming at Hawaii.

This source was too east to be picked up beyond small at the PacIOOS/CDIP American Samoa buoy 7/18-19. The moderate period swell from 175-190 degrees is modelled to have onset locally on Wednesday 7/22. It should be filled in by Thursday 7/23 to near the summer average. It should slowly drop Friday down toward background levels.

The second source was stronger to severe gales. The low center was near 65S, 170W 7/15. It tracked east passing east of the Hawaii swell window 7/17. Seas grew to about 25 feet aimed well east of Hawaii. Angular spreading should bring in low, long-period swell locally. The onset stage is due Thursday 7/23. It should be filled in near average Friday 7/24 from 175-185 degrees. It should drop below average Saturday 7/25.

Below is the collage of the maps of July 14 through 17 on which you should be able to identify the second fetch uncle Pat describes. I particularly like the fetches on the 16th, although not aimed directly at Hawaii. As ususal, it's very hard to guess what we'll get out of an angular spreading, this is one of the cases in which buoy readings and webcam observation will make the final call (which should always the case, actually).


In the end, no fetches on the maps would justify a period of 18s with a SSW direction (that's why I don't trust the direction indication), but what counts is that the buoy is feeling it (period and size are much more reliable). The webcam will tell us how big/consistent its sets will be. I believe the remaining 13s energy of the previous swell will still provide most of the energy. Check the Lahaina webcam if interested, for size, conditions and consistency. Here's a wonderful line in the 5.20am darkness. Guy is scoring uncrowded waves for at least... 10 minutes!


North shore
Pauwela
5.1ft @ 9s from 52° (ENE)            

With 5ft 9s from 52, Hookipa and eastern exposures will have mushy waves up to head high. Below are the maps of July 18 through 20 which show the elongated and unobstructed but overall fairly weak fetch, hence the relatively short period (and consequent denomination of "windswell" for Hawaii... it would be epic in other parts of the world).


Wind map at noon (the other ones can be found at link n.-2 of GP's meteo websites list in the right column).


Fetches map (circles legend: red: direct aim, blue: angular spreading, black: blocked, yellow: apparent direct aim, but out of the great circle ray map, so not 100% sure).
North Pacific (about 4 days travel time from the NW corner of the North Pacific):


South Pacific (about 7 days travel time from east/west of New Zealand):


Morning sky.