Monday, March 2, 2009

Surf for Tuesday – new W-WNW swell moving in

We will have some new waves on Tuesday but, thanks to conditions, I am not sure it will be a full out surf day.

New W-WNW swell (270-300) coming from a storm just off the California coast is just starting to fill isn’t showing much yet, but it will continue to build through tomorrow morning and start to peak sometime in the evening (holding waves into Wednesday). There is also a touch of background SW swell in the water that will strengthen more as we head into the middle of the week.

Check out the CDIP right can actually see the new swell being fed into the model. It isn’t hitting the beach yet but the “potential” is starting to show.

This is sort of a “nerd alert” so if you are just looking for surf then skip ahead...

This is a great time to talk about one of the issues of the CDIP model...particularly this graphic that covers the SoCal Bight (the area from SB down through San Diego and includes the nearshore islands). The CDIP model has a particular weakness...basically it initializes the graphic image off of data from a this case the Harvest Buoy that sits outside of Point Conception.

The computer that runs the model basically takes the data from the Harvest Buoy and says “OK if this is what is showing here, at this fixed point, then this is how the swell would interact with the rest of the Socal Bight). Unfortunately it doesn’t account for the time difference between the buoy and the potentially the model could have a several hour difference between the jump in the “colors” on the image and actual waves at the beach.

This is particularly maddening for W-NW swells because it will show energy that hasn’t hit the beach yet...but it does mess with us on S swells too because the Harvest Buoy is higher in latitude than most of the rest of by the time it shows on this model then it has already hit the beach.

The CDIP guys actually have a FAQ that talks about this... CDIP FAQ

But this is the section that is particularly relevant...

"The model only simulates waves arriving from outside the islands (wave periods of 8 seconds and longer). It doesn't consider any local generation of seas.

To create the image, deep water wave data is collected by a Datawell buoy in 549 meters of water, about 19 kilometers west of Pt. Arguello. This data is transferred to the Coastal Data Information Program at Scripps at approximately 30 minute intervals.

The buoy data is processed to produce an estimate of the deep water directional spectrum (shown at the bottom left of the image). Because there is a time difference between the time the swell reaches the buoy and the time it reaches the beaches, the image is not really a "snapshot" of estimated heights. For a swell from the W-NW, the lag between a swell reaching San Diego after being measured at the buoy is typically around 6 hours or so, making the image more of a short range forecast for San Diego. However, for a south swell, the waves have pretty much hit all the Southern California beaches before reaching the buoy, making the estimates of a south swell more of a hindcast. "

This is another good example of the “need” to have a lot of tools in your forecasting toolbox...anyway I just thought I would share and try and shore up a little of the “Great the model says there is surf but it is flat right now...WTF?” confusion.

End “nerd alert”...

So back to the surf...with this new W-WNW energy and the touch of SW swell...I am expecting the average exposed spots to be in the waist-chest high range for tomorrow morning with some shoulder high sets mixing in at times and becoming more consistent by the end of the day.

The Standout W facing spots, mostly in San Diego, Ventura, and the South Bay...will have surf in the chest-shoulder high+ range fairly consistently. There will be some head high sets mixing in early and I expect some overhead sets coming through by the afternoon.

The winds may be an issue...current forecasts are not calling for a lot of onshore flow but some of the models are showing some W-NW flow, around 5-8 knots, through the morning and some 10-12 knot bump by the afternoon. It may lay down in the evening but a lot will depend on how much pushes through midday.

Personally I think this swell has potential to be fun...I wish we could count on the wind but thems the breaks. I am probably going to get up early and do a cam check (and look at some of the sites out there that carry real-time winds) just to see if it is chunking up the conditions. This is a pretty democratic swell so a lot of spots will be able to pull it in...basically Santa Barbara on down to San Diego...just expect the biggest shape at spots that normally do well on W-WNW swells.

We can expect sort of stacked up windswelly shape no matter what the wind is is just the nature of the swell, but if you have a spot that focus the energy, (or a point that can groom it out a little bit), you might get some better sections. That is all I got for now (sorry for the super-duper long post)...cross your fingers that the winds can stay down.

Here are the is a weird tide swing day...

12:29AM LST 4.9 H
08:45AM LST 0.5 L
The next high tide is on Wednesday @ 01:47AM LST (4.8 H)


kaser_one said...

Hey Adam,

How much weight do you put on the "Nowcast" model on CDIP?,2,3&xitem=spc

I've been using it for the past couple weeks and its been pretty effective.

Surfy Surfy! said...

Great post Adam, thanks.

Seth said...

Wind looks ok right now...gonna chance it in the morning

Adam Wright said...

thanks Surfy!

Kaser - It sort of depends on the swell...I think it is pretty accurate overall. At minimum, even if the wave heights are off, it does a good job of showing the refraction.

All of the nowcast models use the same program to create the model image (it is some shoaling formulas that are overlaid onto MATLAB or something like it...they may have changed it)...they just change the resolution and the buoy they initialize off of as they narrow the focus onto a smaller region. That one you have there is a good one for North OC...but I don't like that the San Pedro buoy is so shadowed by Catalina for the S swells.

I generally take all of the models, buoys, and other tools with a grain of salt...I have a pretty good grasp of the operational weaknesses in all of them. I think it is good to look at as much data as you can...and use the bigger picture to try and fill in some of the gaps in the individual data sources.

Anonymous said...

the end is friggin near, man! I'm so tired of these conditions it ain't even funny. what the hell is going on??? if it ain't one thing it's another. frustrated as a mofo!!!!!