Tasman Sea storm

Bob McDavitt says “when the HIGH gets to 1030 the weather gets dirty”.

Dorothy has been following the Tasman Sea storm that is walloping Tasmania and New Zealand over the next few days. In the image above you can see ADAGIO at 25 S Lat snugged up in Platypus Bay alongside the world’s largest sand island (Fraser Island). We are headed for Tasmania at 43 S Latitude. This week would not be the best time to complete our journey to Hobart.

The color shadings represent sea state, where the dark red in the center is 10 meters or greater. In that sea state we would expect to encounter an 18 meter wave about every 3 hours.

We have uploaded an animated movie showing the evolution of this system, which is being diverted south of Australia by a 1042mb high pressure system west of Tasmania and south of Perth (it was 1044mb yesterday!!).

So it will be a few more weeks before we start pressing hard to get south.

Wave models and sea state forecasting

If you are crossing oceans you are probably keenly interested in forecasting sea state. The most popular wave model today seems to be WaveWatch III (here is a matrix of the key operation models). For interpretation of the wave models we recommend the MetEd educational program for meteorologists (COMET).

Relevant to sea state forecasting, see Analyzing Ocean Swell and Operational Use of Wavewatch III.

Regional Oceanography: an Introduction

Figure 19.7: The ITCZ and the SPCZ.

We discovered this textbook whilst researching the SPCZ (South Pacific Convergence Zone).

Regional Oceanography: an Introduction is a textbook suitable for an advanced undergraduate course or for a course to introduce graduate students to the essentials of oceanography.

(…) Tomczak, Matthias & J Stuart Godfrey: Regional Oceanography: an Introduction 2nd edn (2003), xi+390p., figs., tabls., ind., 25 cm ISBN: 8170353068 (hardcover, US$89.95), 8170353076 (paperback, US$29.95).

You can download each of the chapters [PDF] here.

Techno: Weather and Routing

Warning to Old Salts: we wrote this page in response to requests from friends just starting out cruising, so we tried not to assume a lot of prior experience with weather or passage-making.

Preamble and our biases: When we know as much about weather as Jim Corenman and Stan Honey, we will feel qualified to publish a bit more information on the topic here. We spend a fair bit of time studying weather – especially in the context of the onboard forecast at sea. Back in the late 1960s we decided to get involved in yacht racing because we believed it would accelerate our seamanship learning curve (we think that is true, and highly recommend that to anyone planning to go cruising). With regard to weather forecasting, there is no doubt that our forecasting skills are sharpened by working with seasoned professional weather routers on our passages.

Sitting in an armchair reading a good mariner’s weather book is great – but what really focuses your mind is choosing a weather window, and more importantly, managing your way through what unfolds on the real-world ocean. Having the benefit of a professional’s thinking while trying to figure out the relevant weather patterns is a superb learning opportunity. We don’t think these services are expensive – rather the inverse. It is quite remarkable how much service the routers we know provide for such a modest fee.

A possibly non-obvious, but very important benefit of having the services of a professional router is the enroute guidance. Our enroute approach is usually based on asking our router to monitor our passage plan vs. our actual daily progress vs. the real-world weather developments. We ask that our router contact us by Inmarsat Sat-C, Iridium, or Sailmail if his interpretation changes enough to justify a change in our routing plan. E.g., a “speed limit” as we agreed with Rick in our last Tasman sea crossing (we slowed down no more than 7 kn to allow a Fiji-borne low pressure system to pass in front of us).

In the following, some of the resources we provide have a distinct Pacific perspective. That is where we are and what we care about right now. If you are cruising the Red Sea, there may be much superior resources to be found.

Please keep in mind that strong winds are not the worry on passages, it is the sea state. A 60kn squall tests your preparedness and seamanship, but it is 30-ft waves that might actually give you a challenge. Further it is not just how big the waves are, but whether they are breaking that is the real issue. Big Southern Ocean non-breaking waves can make for a thrilling ride, but properly handled should not be a danger, so long as you keep your speed under control to avoid broaching or “submarining” your bow(s). Big breaking waves are really the main threat to a small boat on passage. Fortunately, they are not very common, and with enough attention paid to weather outlook, the alert passage-maker is unlikely to encounter such seas (unless doing long passages in the Southern Ocean — e.g., NZ to Patagonia).

Which provokes one further comment from Adagio – we have read of (and met with) various yachts that have encountered threatening sea states. That is why the first-listed resource below is Victor Shane’s Drag Device Data Base. When we read 99% of these reports, we ask ourselves “what the heck were they doing out there in that place at that time?”. Of course, that doesn’t directly apply to the “Queen’s Birthday Storm of 1995“, as conditions did not look all that challenging prior to the start, though we believe the best routers or weather-hounds would have suggested changes in route once underway. Just 200nm change in your position relative to a system can make a very big difference.

“Stuff happens out there”, so regardless of your weather skills and resources, you and your yacht should be prepared for the worst that might happen. That said, the odds are with you when you have done your weather homework, and exploit first-class routing advice. I don’t have valid statistics to quote, but believe that the maximum risk most cruising yachts encounter is when close to land, and that the big majority of stuff-ups happen when anchored. Land is hard, water is soft, stay with the boat until it sinks beneath you (and obviously, we think it’s a good thing to sail a yacht that has inherent buoyancy, like Adagio).

Closing comment – pay attention not only to the weather outlook, but also to the currents and bottom contours you are planning to sail across. Currents contrary to the sea-state, or significant sea mounts or shoaling can produce dangerous sea-states. So don’t be there when conditions aren’t moderate! If a bar crossing is required, please investigate all available local knowledge before attempting the bar.

Rick Shema, Weather Routing

Rick Shema has helped us with all of Adagio’s passages so far. That we keep returning to enlist Rick’s services indicates that we place a high value on his advice. Rick delivers very personalized service, and follows-up closely on the value and accuracy of his information. Highly recommended.

DDDB, Drag Device Data Base

Victor Shane’s Drag Device Database made it possible for Steve & Dorothy to decide to go cruising on a catamaran, rather than a monohull, upon which all their 30-odd years of sailing experience were based. We should say, Victor’s DDDB, plus Carl Schumacher’s advice and counsel (“are you more concerned about being upside down on the top, or being right-side-up on the bottom?”). Consider this (our personal view), most yachts that have bad experiences find those challenges at anchor, or due to inter-personal crew problems. Yachts that encounter really serious problems at sea are rare. Yachts that encounter serious weather and sea-state problems at sea are even more rare. Yachts that attempt to moderate such severe sea-state conditions by use of a sea anchor or drogue (i.e., a drag device) are even more rare. Yachts that have encountered the union of those conditions, and filed an objective report are seriously rare. That is the challenge that Victor Shane faces as he endeavors to compile an objective report of real world experiences, and to distill from same what lessons may be inferred. Visit the site, buy the DDDB book, study it, understand and rehearse the methods described therein, and you will most likely never need to use them “in anger”, but you will then be prepared and forewarned.

Nobody has a “silver bullet” that will guarantee you survival of whatever you may encounter at sea. Simply, our view is that if you do not study the DDDB information carefully so as to draw your own conclusions regarding gear and strategy, then you have not done your homework. And do not conclude that with the appropriate gear and training, that you will always be comfortable. We have not personally experienced this, but cruising friends of ours have, a sea anchor may help you manage a storm you should have avoided, but it may still be bloody uncomfortable – sometimes the seas are well-organized, sometimes there are vicious cross seas. With some luck Adagio won’t be reporting to DDDB on the latter case, but it does happen as it did to John & Dianne Furgeson on Never Monday on their passage from Fiji to New Zealand.

Mariner’s Weather Handbook

The Dashew’s weather book – if you can have only one, this is the one. Back home in NZ, we have perhaps three dozen weather books. Only two made the weight-analysis budget to come aboard Adagio. And in the case of Mariner’s Weather Handbook, we could have just carried the CD-ROM. We allowed the weight because we value the ability to read and reread sections of this book comfortably.

Jim Corenman taught us the importance of understanding upper level (500mb) analysis and prognosis information in 1995. Mariner’s Weather Handbook is the only book we know of that addresses this topic in-depth and for our audience. We have a graduate-level weather textbook (back in NZ) that covers this essential weather-as-3D-problem topic, but this is the book that makes it practical and useable aboard.

Commanders Weather, Weather Routing

Another popular routing service — which we used in 2000 and 2001, and were pleased with the service, though we prefer working with a single meteorologist from planning to landfall, 24×7.


This is another model we look at regularly, from the European Centre for Medium-Range Weather Forecasts. It is particularly useful for studying the 500mb situation, as they give hemisphere view options. This makes it much easier to study long and short-wave trends. I don’t know why, but they don’t publish time=0 data on their public website, at present you can see days 3 to 6.

Oceanweather, Global Sea State

This is a commercial site with some interesting free resources. Among other resources, is this global sea-state model. It won’t tell you whether you have a weather window, but it will tell you what is happening today. And if you study this model over a period of time it will give you useful info about what can happen where you are planning to go.