PredictWind? Weatherfax? What weather system do you recommend for crossing oceans?

[Paul L]

Originally Posted by Auspicious

Agreed. Land effects including katabatic winds and thermally driven winds make a difference near islands. In my experience those are generally predictable from the macro-level synoptics and the navigational charts.



....

Well sure if you know the area. Most of the places we go it is our first time, so you can't use your great interpretive knowledge to know what local conditions will be like. We are just finishing up 2,000 miles of crossing Indonesia. Every area we've been in has had its 'special' weather conditions that you would only know after years of local observation.
That's part of tbe fun of cruising.

[Auspicious]

Originally Posted by Paul L

Well sure if you know the area. Most of the places we go it is our first time, so you can't use your great interpretive knowledge to know what local conditions will be like.

Sure you can, and in this case I do mean you. You're a smart cookie.



You've got the macro level conditions from gribs or synoptics. You have nav charts. The latter may not have the detail of topographic charts but the little '+' marks with maximum altitude help. So do cruising guides where key words like "rugged," "mountain," or "flat" are hints.



With your experience, looking at the wind forecast (especially if you can do overlays, e.g. synoptics in OpenCPN) you can predict funneling between islands and if you can predict the wind shift from a front passage you can predict funneling. Altitude is straight forward to katabatic effects. Thermal is hardest. You have to look out the window at cloud cover and remember that land has less thermal inertia than water. Some of these effects vary with environmental conditions, mostly sunlight and the impinging wind speed and direction.



My suggestion is to do some of your own island effect prediction as you approach a new-to-you landfall and see how well you do. I bet you do pretty well and get better and better with time.



What else are you going to do? Clean the toilet? Scrub behind the cooker? Those can wait until you are at anchor. Do take a shower and clean up for the nice C&I people. *grin*

[Paul L]

Originally Posted by Auspicious

Sure you can, and in this case I do mean you. You're a smart cookie.



You've got the macro level conditions from gribs or synoptics. You have nav charts. The latter may not have the detail of topographic charts but the little '+' marks with maximum altitude help. So do cruising guides where key words like "rugged," "mountain," or "flat" are hints.



With your experience, looking at the wind forecast (especially if you can do overlays, e.g. synoptics in OpenCPN) you can predict funneling between islands and if you can predict the wind shift from a front passage you can predict funneling. Altitude is straight forward to katabatic effects. Thermal is hardest. You have to look out the window at cloud cover and remember that land has less thermal inertia than water. Some of these effects vary with environmental conditions, mostly sunlight and the impinging wind speed and direction.



My suggestion is to do some of your own island effect prediction as you approach a new-to-you landfall and see how well you do. I bet you do pretty well and get better and better with time.



What else are you going to do? Clean the toilet? Scrub behind the cooker? Those can wait until you are at anchor. Do take a shower and clean up for the nice C&I people. *grin*

Ah you are just a much better meteorologist than I ever will be.
You really cannot predict if the SE tradewinds will wrap north up the strait between islands and turn into westerly winds on the north side, or if the trade will bunch up over the island and be katabic in the anchorage or if the trade will wrap around the corner and hug the north coast or it will be dead calm without local experience. I've seen all of these in the last months in anchorages that should be protected.

[Auspicious]

Originally Posted by Paul L

Ah you are just a much better meteorologist than I ever will be.
You really cannot predict if the SE tradewinds will wrap north up the strait between islands and turn into westerly winds on the north side, or if the trade will bunch up over the island and be katabic in the anchorage or if the trade will wrap around the corner and hug the north coast or it will be dead calm without local experience. I've seen all of these in the last months in anchorages that should be protected.

Well first, you're in the opposite hemisphere from me, so I have to slow down and think harder.



The key to solving complex problems is to break them down into multiple smaller problems. If you think in terms of component forces it gets easier. We're never going to be perfect but we can get close most of the time.



Are the trades running light or heavy? Is there a Low or front that drives a pressure change that will cause a supporting force? How high is that mountain (remember katabatic is gravitational wind, not just swirling in a small space - that's more like funneling). Are the trades running more S or SSE than SE leading to more westerlies in the gap? Or are they ESE or E and driving easterlies. Lots of cloud cover leading to light thermal effects or the sun beating down so you see big thermal shifts driving sea breezes and land breezes.


My suggestion is some time with Reed's Marine Meteorology (academic) and Gentlemen Never Sail to Windward (experiential). Both are focused on the northern hemisphere so you'll have to flip some things around.



Local knowledge in this case is an excuse for not understanding the effects and how they combine. You have to memorize a lot more for local knowledge to be helpful. If you understand why something is happening you can figure more out. Still no substitute for knowing just where that rock is *grin* or that there is a steep canyon that always pushes the breeze out of a narrow bay.

[Paul L]

Originally Posted by Auspicious

Well first, you're in the opposite hemisphere from me, so I have to slow down and think harder.



The key to solving complex problems is to break them down into multiple smaller problems. If you think in terms of component forces it gets easier. We're never going to be perfect but we can get close most of the time.



Are the trades running light or heavy? Is there a Low or front that drives a pressure change that will cause a supporting force? How high is that mountain (remember katabatic is gravitational wind, not just swirling in a small space - that's more like funneling). Are the trades running more S or SSE than SE leading to more westerlies in the gap? Or are they ESE or E and driving easterlies. Lots of cloud cover leading to light thermal effects or the sun beating down so you see big thermal shifts driving sea breezes and land breezes.


My suggestion is some time with Reed's Marine Meteorology (academic) and Gentlemen Never Sail to Windward (experiential). Both are focused on the northern hemisphere so you'll have to flip some things around.



Local knowledge in this case is an excuse for not understanding the effects and how they combine. You have to memorize a lot more for local knowledge to be helpful. If you understand why something is happening you can figure more out. Still no substitute for knowing just where that rock is *grin* or that there is a steep canyon that always pushes the breeze out of a narrow bay.

Let's see, the best models in the meterological world don't get it right. The forecasters don't get it right. But you are going to look at the topography and synoptic chart and call it right with zero local knowledge. Which of the three volcanic cones on the island are you going to call as the dominate factor, or even a relevant factor at all? Is the strait between to islands going to howl the trades through or be dead calm (Hint the height of the volcanoes on either side isn't going to predict it)? I'm thinking you are being a little optimistic in your ability to accurately forecast a complex area you have no experience with - OK, just a tad optomistic.

We were in an area with relatively stong SE trades actually running a few weeks back. We selected an anchorage well protected from the east and south with exceptable depth. It actually had westerlies. Had to leave and move on that day. There is zero chance I would have forecast westerlies in the running strong SE trades situation without having been through it and seen the conditions.

[Paul L]

Back to the original subject of this post. I was talking to another cruiser last night and they told me a story about using Predictwind. They were anchored in an area of complex reefs. Late afternoon they checked PW. One of the PW adjusted models (not GFS or Euro) showed 40kt plus winds coming through the anchorage. The standard models showed no change. They and a couple of other boats picked up the anchor and risked passage through the reefs in be late afternoon to a more secure anchorage. The winds didn't arrive. It was the last time they looked at the PW adjusted models.

[Auspicious]

Paul, et al,

I'm going to have to break this into pieces.

Originally Posted by Paul L

Let's see, the best models in the meterological world don't get it right.

This is correct for two reasons: the models which generate gribs make some assumptions regarding continuity of first and second derivatives of weather elements. This is necessary in order to solve the equations in a timely fashion. It's also why gribs don't show fronts. Second the models we use aren't designed for small areas. They are macro models. Interestingly there ARE some increasingly good micro-scale models. The NOAA Operational Forecast Models (OFS) are quite good and DO account for topographical effects. The first of them in operation was CBOFS for Chesapeake Bay and has been very accurate. It uses macro elements as input data so it even does a decent job of showing the effects of fronts. Striking.

Originally Posted by Paul L

The forecasters don't get it right.

Again this is due to the macro scale of meteorologist value-added forecasts. I suspect that most forecasters at the Ocean Prediction Center would struggle with micro-scale forecasts ("struggle" means here they wouldn't be a lot better than me *grin*) because they don't do it often. The forecasters on the OFS development team have more practice (they are after all building the tools) and would probably make my head spin.

Let's not forget that the meteorologists at OPC and UK Met and Deutscher Wetterdienst and elsewhere have access to a lot more data than we do when developing their forecasts. They have ensembles of model data, weather balloon data, radar and IR and visual overhead imagery, and data from VOS and CWOS and other calibration data points. Not only are they better trained than we are they are better informed. That is why synoptics are so much better than gribs. Still not "right" but close enough, and the best available options.

Originally Posted by Paul L

But you are going to look at the topography and synoptic chart and call it right with zero local knowledge. Which of the three volcanic cones on the island are you going to call as the dominate factor, or even a relevant factor at all? Is the strait between to islands going to howl the trades through or be dead calm (Hint the height of the volcanoes on either side isn't going to predict it)?

I didn't say and I'm not saying I'll get it right. I'm saying I--and you--can get it close. For your volcano scenario it depends. If the peaks are close together they'll act as a monolithic factor. If they are far apart they will each act individually. Remember to account for funneling in between peaks which, when the macro wind is up, will be more significant than katabatic effect. For the strait between islands it also depends. What is the orientation of the wind with respect to the nominal axis of the strait? How wide is the strait? Is the strait straight? *grin* Might the shape of the land or curvature of the strait generate lift like a sail or a wing? Will air flow stay attached or detach? The cruising guide can help there also.

I did leave out one other important tool in our bag. We are on the spot. We can look out the window. If my assessment is that the SE trades are SSE and the wind will wrap around the South end of the island and the strait to the North will be light to moderate Westerlies I can see as we approach that I might be wrong. I look out the window. I can adjust. I'll still be smarter than I would have been without having done the work. In point of fact this is like what the meteorologists do when they adjust their forecasts using reported actual data from VOS. For us it's just a little more real time. It isn't like we're going really fast. *grin*

Originally Posted by Paul L

I'm thinking you are being a little optimistic in your ability to accurately forecast a complex area you have no experience with - OK, just a tad optomistic.

We were in an area with relatively stong SE trades actually running a few weeks back. We selected an anchorage well protected from the east and south with exceptable depth. It actually had westerlies. Had to leave and move on that day. There is zero chance I would have forecast westerlies in the running strong SE trades situation without having been through it and seen the conditions.

I may be optimistic. Unlikely as I'm a contrarian by nature. I don't trust anyone including myself. I do have the benefit of formal training in fluid dynamics which helps, even as long ago as it was, as well as some formal training and a lot of self-taught work in marine meteorology. I practice a lot. What I've described at a high level has worked well in the Leeward and Windward Islands of the Caribbean, in the Skagerak, the Bahamas, and the Florida Keys. All admittedly in the Northern hemisphere. For the Southern some things would flip.


You and others probably already do some of this yourself. You don't have to have run up the Potomac River or the Ashley River or NY's East River to predict that funneling will likely swing the wind along the axis of the river. You can predict a short term shift (and what it will be) where a river enters a bay or the sea. What I describe is simply more of the same with a larger set of inputs.

[Paul L]

Dave
Your getting a little long winded. This is a forum not a podium��

Using the Eastern Carib as an example is pretty meaningless. The E Carib is about the easiest place to cruise among the popular cruising grounds (barring crowds and crime). The trades are so predictable and the islands are arranged so most of the sailing is a reach. You pick your anchorage and go. It isn't all of sudden not going to be sheltered.

Basic understanding of weather is a skilled needed by cruisers - On the job training or classroom. Local knowledge is an important part in interpreting and forecasting weather. The passage strategy for Chesapeake to Virgin Islands, Fiji to New Zealand or down the Mozabique passage are not the same, even if they all have highs and lows.

[jackdale]

Originally Posted by Paul L

Basic understanding of weather is a skilled needed by cruisers - On the job training or classroom. Local knowledge is an important part in interpreting and forecasting weather. The passage strategy for Chesapeake to Virgin Islands, Fiji to New Zealand or down the Mozabique passage are not the same, even if they all have highs and lows.

Exactly! (not too long winded, I trust)

[Auspicious]

Originally Posted by Paul L

Dave
Your getting a little long winded. This is a forum not a podium

Paul - You asked me a question. I gave you a complete answer.



Sorry you leapt on the EC and left out the Skagerak. No trades there!



I'll leave it with cruisers can make actionable micro-forecasts in way of islands and other topographical factors. See Denton Moore's Gentlemen Never Sail to Weather and Reed's Marine Meteorology. I think Evans Starzinger wrote a few articles as well. If you get to my part of the world I can introduce you to the professionals working on NOAA OFS.

[nofacey]

To OP.....IridiumGO vs SSB depends upon ability to receive at the right time, and that can vary heavily with the radio.....not so much the GO.

Just finished a circumnavigation, started off using SSB. Once away from North America, I got very tired of getting up at weird hours for long periods trying to get complete downloads....neither method is fast. By the time we hit the Indian Ocean, I’d given up on SSB as primary, and was using GO/Predictwind. Got my info reliably when I needed, updated multiple times a day (PW tells you when next update occurs).

Last leg home, a weird & strong low popped up on path. PW let me see far enough ahead to dodge, while my usually reliable weather router missed till it was too late.

No system is perfect, but the GO/PW combo puts key info in your hands reliably, when you need it.

[Paul L]

Originally Posted by Auspicious

Paul - You asked me a question. I gave you a complete answer.



Sorry you leapt on the EC and left out the Skagerak. No trades there!



I'll leave it with cruisers can make actionable micro-forecasts in way of islands and other topographical factors. See Denton Moore's Gentlemen Never Sail to Weather and Reed's Marine Meteorology. I think Evans Starzinger wrote a few articles as well. If you get to my part of the world I can introduce you to the professionals working on NOAA OFS.

I'm not clear what you are disagreeing with. All long distance cruisers interpret the forecasts and make decisions of what they think the actual local conditions will be. You seem to say that this is a very accurate operation for you. I've said that the local knowledge is extremely important in getting these calls right. As a long distance cruiser you are continually going into new areas that have amazingly different local phenomena. After some experience in the area you get much better. Using general, weather knowledge does not lead to a high prediction success rate without knowledge of the local conditions.

Since we've been cruising the last few months in Indonesia we've been in areas that are in their rainy season while others are in their dry season at the same time. Until being here I would never have even thought it possible. Right now I'm trying to work out local weather conditions in the transition period between SE monsoon season and NW monsoon system. Best info is asking locals who deal with it daily.

So maybe our disagreement is simply a matter of degree. You believe the local interpretation will be very accurate. I am far less optomistic in many areas.

I have sailed your area. You actually brought out the Icom guy during an boat show">Annapolis boat show to reprogram the MMSI on my 802. Thanks. We then did tbe Salty Dawg rally to the Virgins that had all the Mayday calls after the shore router forecast didn't pan out too well.

[Auspicious]

Originally Posted by Paul L

All long distance cruisers interpret the forecasts and make decisions of what they think the actual local conditions will be. You seem to say that this is a very accurate operation for you.

I would not go so far as to say very accurate, but accurate.

Please forgive me for getting long-winded again. I'm a story teller. In this case I'm surely going to offend someone here. *sigh* In my professional career there was an insult that someone was a "handbook engineer." The implication was that a handbook engineer would look something up and use it. A real engineer would look something up (you can't remember everything), look at it and say "there is something wrong with this answer - that can't be right."

The analogy is a stretch here. Dependence on local knowledge is handbook engineering. You're dependent on the source and your application of that knowlege. Learning and applying more of the science makes you more self-sufficient and gives you the opportunity to assess what you "look up."

So when I show up somewhere I haven't been before I can and do make an assessment of the micro weather elements.

To my mind--another analogy--this is the difference between passing a ham exam by memorizing questions and answers and passing by learning the material. When you learn the material you can apply the knowledge outside the single application of the question on the test.

Consider a spectrum of application. At one end you simply memorize local knowledge; or maybe you do, I have to write things down. *grin* You can analyze enough of that local knowledge, including boundary conditions, and synthesize a theory, subject to validation to explain the local knowledge. That is indeed what science is about. Fortunately this work has already been done (and continues) by people for whom it is their life's focus. Why not take advantage of that knowledge? Why not study to learn it, apply it, and do better?

I know I come across as difficult. I try to show that we can all be smarter and stand on the shoulders of giants. We can't be experts on everything but we sure as heck can learn enough to be competent in a lot of fields. Cruisers need to. Either that or run up a lot of miles on a credit card.

Originally Posted by Paul L

So maybe our disagreement is simply a matter of degree. You believe the local interpretation will be very accurate. I am far less optomistic in many areas.

Strike the "very" and I'll agree with you.

Your observation of adjacent wet and dry seasons is on point. One can accept that and memorize it or ask "why?" and do research to learn what is known. That puts you in the position of recognizing a pattern (weather, topography, whatever) somewhere else and act accordingly.

Originally Posted by Paul L

I have sailed your area. You actually brought out the Icom guy during an Annapolis boat show to reprogram the MMSI on my 802. Thanks. We then did tbe Salty Dawg rally to the Virgins that had all the Mayday calls after the shore router forecast didn't pan out too well.

I remember both of those events. The initial phone call to the Icom guy was really interesting. It was surprisingly easy to convince him to come. I think he really wanted to get out of the booth. I know have my own "magic cable" and software for that.

It does go to show that even professional meteorologists don't always get things right. Sometimes they miss things. Sometimes the weather evolves unpredictably. We can look back on what happened and learn from it. At least we move from not knowing what we don't know to knowing what we don't know. Then we can look.

Maybe this is just another reflection of Citizen Science like the water sampling in the Pacific.

[Paul L]

Originally Posted by Auspicious

..

The analogy is a stretch here. Dependence on local knowledge is handbook engineering. You're dependent on the source and your application of that knowlege. Learning and applying more of the science makes you more self-sufficient and gives you the opportunity to assess what you "look up."

....

Yes, it is so much of a stretch that I don't see it applying at all.
When I've been around an area for awhile, my ability to interpret the forecasts for my passage and anchoring uses is far better than when I first show up. Getting local info from people who have been there before increases my ability to interpret weather forecasts and apply them. 400 years of pilots books has sort of fleshed out this approach.

But enough of silly forum bantering. I'll let this one lie.

[Exile]

Originally Posted by Auspicious

* * *

Please forgive me for getting long-winded again. I'm a story teller. In this case I'm surely going to offend someone here. *sigh* In my professional career there was an insult that someone was a "handbook engineer." The implication was that a handbook engineer would look something up and use it. A real engineer would look something up (you can't remember everything), look at it and say "there is something wrong with this answer - that can't be right."

* * *

Can't comment on the nuances of local weather forecasting skills, but your analogy to "handbook engineers" parlays nicely in my mind with your admonition to be "beware of cut & paste sailors."

I have several friends who are retired engineers -- two of whom that I often sail with -- and I'm constantly teasing them about "going too deep" with their problem solving. "ZOOM OUT, ZOOM OUT" is an oft-repeated refrain on my boat! I mean, really, does it matter if the markers on the anchor chain wind up lying a few inches above or below the water line?? But truth be told, I much prefer the attention to detail -- and ability to engage in independent analysis -- than the superficiality which all too often only serves as a poor "cut & paste" or "handbook" substitute for in-depth knowledge. So long as the anchor remains properly set, right?

And now for a little levity . . .