What do these swell numbers say (or not)?

[davidbaraff]

So checking a forecast for this weekend, I see these numbers:

SAT
NE WINDS 5 KT...BECOMING W IN THE AFTERNOON AND EVENING.
WIND WAVES LESS THAN 2 FT. W SWELL 4 TO 7 FT.

SUN
NE WINDS 5 KT...BECOMING W IN THE AFTERNOON AND EVENING.
WIND WAVES LESS THAN 2 FT. W SWELL 4 TO 6 FT.

Obviously, wind waves less than 2ft sounds good. If you're shore diving, does W Swell of 4-6,7 feet mean much? How about if you're out on a boat?

And is a swell prediction on Tuesday worth much of its weight for Sat/Sunday?

Just starting to learn how to make a reasonable prediction for a coming up weekend; any pointers or advice greatly appreciated.

 

[Gombessa]

So checking a forecast for this weekend, I see these numbers:

SAT
NE WINDS 5 KT...BECOMING W IN THE AFTERNOON AND EVENING.
WIND WAVES LESS THAN 2 FT. W SWELL 4 TO 7 FT.

SUN
NE WINDS 5 KT...BECOMING W IN THE AFTERNOON AND EVENING.
WIND WAVES LESS THAN 2 FT. W SWELL 4 TO 6 FT.

Obviously, wind waves less than 2ft sounds good. If you're shore diving, does W Swell of 4-6,7 feet mean much? How about if you're out on a boat?

And is a swell prediction on Tuesday worth much of its weight for Sat/Sunday?

Just starting to learn how to make a reasonable prediction for a coming up weekend; any pointers or advice greatly appreciated.

I'll leave the boaters to interpret, but for shore diving, this looks great. Assuming you cut and pasted this from the report with the "Pigeon Point to Point Pinos" header, it basically means Monterey Bay will get some shelter from the west swell courtesy of the peninsula. By the time the waves enter the bay, they've usually dissipated--you're not going to see 6ft high breakers over the beach, for instance. With a 4-6ft west swell report, you're likely to some very smooth, calm surface conditions at most Monterey sites.

We typically have diveable shore conditions somewhere in Monterey or Carmel if the swell reports are under 10-12ft, but whenever it gets above 8ft, I'm watching the shore for at least 20 minutes before making the call whether to dive or not.

 

[davidbaraff]

I pasted it it from a section which simply said: "Monterey Bay".

If I paste from:
PZZ560-161030-
PIGEON POINT TO POINT PINOS TO 10 NM-
847 PM PDT TUE SEP 15 2009

it says:
SAT
NW WINDS 10 KT. WIND WAVES 2 FT OR LESS.
NW SWELL 5 TO 7 FT.

SUN
W WINDS 10 KT. WIND WAVES 2 FT OR LESS.
NW SWELL 5 TO 7 FT.


so the only difference really is NW rather than W. The Monterey Bay one isn't as relevant?
FYI, the URL I'm using is: NDBC - NWS Forecast.

 

[eric gundrum]

David, you probably want to have a look at Chuck Tribolet's conditions collection page: Monterey Sea Conditions at a Glance

I found it takes a few looks to begin to appreciate it. It may take a lifetime to really understand it.

 

[dannobee]

Here is the offshore forecast. Looks decent for boat diving, too. Somehow the swell is NW and not W as in the 535 forecast. Since it's still early in the week, look for revisions to the forecast, as it will likely improve by Friday's forecast. Call it whatever you wish, but that's normally what happens. I guess they're more conservative with longer time lines. Also, look for the interval and notice that tonight's forecast has the intervals at 10 seconds. That's decent (irrespective of the wind waves). When the swell height equals or exceeds the interval, watch out. It'll be a long, bumpy ride back to the harbor. And strong surge underwater would be likely.

I'll also watch the tides to give an idea of launch ramp and vis. Vis is usually better on an incoming tide when you're shore diving.

Tide Location Selection for California

PZZ560-161030-
PIGEON POINT TO POINT PINOS TO 10 NM-
847 PM PDT TUE SEP 15 2009

.TONIGHT...NW WINDS 10 TO 20 KT. WIND WAVES 3 TO 4 FT.
W SWELL 3 TO 4 FT AT 10 SECONDS.
.WED...NW WINDS 10 TO 20 KT. WIND WAVES 3 TO 5 FT.
W SWELL 4 TO 6 FT AT 11 SECONDS AND S 3 FT AT 13 SECONDS.
.WED NIGHT...NW WINDS 10 TO 20 KT. WIND WAVES 3 TO 5 FT. W SWELL
4 TO 6 FT AT 11 SECONDS AND S 3 FT AT 13 SECONDS. PATCHY FOG.
.THU...NW WINDS 5 TO 15 KT. WIND WAVES 3 TO 4 FT.
W SWELL 7 TO 9 FT AND SW 3 FT. PATCHY FOG.
.THU NIGHT...N WINDS 5 TO 15 KT. WIND WAVES 2 TO 3 FT.
W SWELL 7 TO 9 FT.
.FRI...NW WINDS 10 KT. WIND WAVES 2 FT OR LESS.
NW SWELL 5 TO 7 FT.
.SAT...NW WINDS 10 KT. WIND WAVES 2 FT OR LESS.
NW SWELL 5 TO 7 FT.
.SUN...W WINDS 10 KT. WIND WAVES 2 FT OR LESS.
NW SWELL 5 TO 7 FT.

 

[btroxell]

I wrote something a while back to help people understand the underlying physics of waves. The information won’t help too much in making a decision if diving McAbee is a good idea after reading the forecast but it will help in understanding some of the details like the difference between wind waves and swell and why 10 sec periods sound pretty good. It can be found at:
DiveMonterey.info/WaveDissertion.html

Ben

 

[fisheater]

Ben!

That's a wonderful and informative webpage. Many thanks!!

 

[KRL1973]

In my limited shore diving experience I have found that W swells are not so good and N,NW or S, SW are generally much better. I would think that breakwater to the point would be sheltered from a W swell but have found that not entirely to be the case. I think maybe the waves get wrapped around the point somehow and create sort of a turbulence as a result.

Last Sat I went on a 4-6' W swell and went to Carmel 1st but found massive breaking waves so went to breakwater and it was decent there but by no means ideal. There seemed to be somewhat random sets of waves and the surge was inconsistent as well. The viz was a better than expected 10-12ft. once you got away from the student groups and into 30+ft depth.

good luck!

Ken

 

[Chuck Tribolet]

In my limited shore diving experience I have found that W swells are not so good and N,NW or S, SW are generally much better. I would think that breakwater to the point would be sheltered from a W swell but have found that not entirely to be the case. I think maybe the waves get wrapped around the point somehow and create sort of a turbulence as a result.

Last Sat I went on a 4-6' W swell and went to Carmel 1st but found massive breaking waves so went to breakwater and it was decent there but by no means ideal. There seemed to be somewhat random sets of waves and the surge was inconsistent as well. The viz was a better than expected 10-12ft. once you got away from the student groups and into 30+ft depth.

It depends on where you are. Generally a W swell is better (at the same height and
interval) than a NW swell, esp. in the south end of Monterey Bay and the south end
of Carmel Bay, because there's some protection from a W swell from Pt. Lobos and
Pt. Pinos respectively. Swell don't go throught granite very well.

Saturday's forecast was:

.TODAY...NW WINDS 5 TO 15 KT. WIND WAVES 1 TO 3 FT. NW SWELL 6 TO 8
FT AT 14 SECONDS. SLIGHT CHANCE OF THUNDERSTORMS.

It was not 4-6W. The only south Carmel Bay site I'd think about divng on a 4-6 NW
forecast is Pt. Lobos.

Where were you in Carmel?

 

[Teamcasa]

Also, look for the interval and notice that tonight's forecast has the intervals at 10 seconds. That's decent (irrespective of the wind waves). When the swell height equals or exceeds the interval, watch out.

Exactly. Watch the intervals as well. 10 sec intervals makes for an easy ride even in 8' swells.