The Offshore Voyaging Reference Site

Weather Analysis—Part 1, Tactical

In the first chapters I introduced the concept of strategic weather analysis and the skipper’s responsibility to understand the weather and make good decisions based on that, and then I analyzed hardware and software options.

In this and the next two chapters, this one tactical and the next strategic, I’m going to detail what information I download and, most importantly, how I analyze it.

So imagine we are in a remote anchorage or several hundred miles at sea on an ocean passage (the steps are the same although the goals of the analysis is a little different), and it’s time for our daily look at the weather.

I usually do mine first thing but any time will do, although I do suggest getting into a routine of doing this at the same time each day.

Let’s do it:

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Steve Payment

Great overview. I like how you give a step by step process to creat your own forecast then compare to the pros. Doing it daily also helps learn common weather patterns. Thanks!

Dick Stevenson

Hi John,
Excellent series.
I would want to underline your suggestion that writing it down helps weather/passage/cruising planning in multiple ways. I do not know any data that puts me in a trance like state that leads to forgetfulness faster than weather data.
I will write down the days/dates in 6 hr intervals out 4-5 days or so or longer leaving lots of room. I then, for each time, put down the forecast winds/direction etc for that time from each source I am using. Starting days ahead of time, I then end up with a sense of how the pattern might be evolving, how different forecast sources are seeing the weather etc.
I find that without writing all the information down in this spread sheet/crib sheet manner, I forget and get it all jumbled up.
As you said, it sounds like a pain, but after you reap the rewards of being able to think clearly about upcoming weather and plan accordingly, you may find it quite satisfying. Fitting in well with weather is immensely gratifying. Getting on the wrong side of what Mother Nature puts out can ruin one’s day.
My best, Dick Stevenson, s/v Alchemy


Hi John,

I admit I read this with a bit of trepidation, because I almost always learn something new on here and then have to change how I think about things! However, I was pleasantly surprised that the methods of weather forecasting I’ve developed on my own eerily mimic what you’ve described above. So I feel very good about that! You put it into words very clearly too. Looking forward to the next one.



Good information? From my little point of view the information spread and shared on AAC (including most comments) is invaluable. I have to say, since registering my account here I have upgraded from a lousy to a less lousy sailor, and the reactions of my crews show it. Actually I have been able to implement a lot of Johns (and others) thoughts and ideas on charter boats as well, and it has been helping tremendously.


Thanks for the updated weather book. The options and resources can be overwhelming and you make it manageable to add the indispensable skill of weather forecasting to my skill set.

Henrik Lundin

Hi, first time commenter here!
This was fun to read and a great reminder for me about the “proper” procedure when analysing weather.
I have twice completed a seaweather course held by the swedish meteorolog and sailor Anders Ljungkvist. I can highly recommend them for any swedes reading. His method is very close to your.

Brian Russell

I absolutely AGREE that “writing it down” is a vital step in understanding the forecast and trends. Also totally agree that the weatherfax big picture charts are vital. I get mine at sea for free via Saildocs return email, very quick and easy on the Go.

Cheers from Carriacou,
Brian on Helacious

Michael Jack

Hey, John I am to blame for setting you on the wrong path there. But I still haven’t figured out how to get the UK Met Office surface charts through Saildocs. Did you or is that still to come?

Iain Dell

Sail training in the Royal Navy of the early 80’s it was (sometimes physically!) hammered into me to listen to the shipping forecasts and reports from coastal stations twice daily. Woe betide me if I was ever late. Using a form of shorthand for these lengthy reports, I had to transcribe everything onto paper and create my own charts for UK and Atlantic waters from which I was to produce analyses & forecasts for inspection by the skipper, particularly noting any developing trends. This routine instilled great discipline which served me well – until I became lazy in later years on my own boat and discovered ‘windy’ and its ilk. To satisfy my masochism though I do keep the old skills practiced. Sometimes.

However, there’s just something about the act of writing things down that no app or pre-canned program can ever reproduce. Maybe its the way the mind is wired or perhaps its just an old-fashioned thing, but in me at least, it facilitates a much deeper understanding and not just mere recognition of certain facts. I hope that makes sense!

Jim Schulz

Thanks for this great outline John, especially the par5 about writing down your own forecast. It’s not a step,I’ve done before but will start using it as it seems really worthwhile. Question – why no mention of 500mb charts? I still find them useful as part of the pattern recognition learning you mention. Are they more of a strategic than tactical tool or do you think they push you into the “too much information” trap?

Tim Sowerby


I’m definitely a novice who, despite reading about the weather, until now, simply did not know where to start. Thanks for a clear plan of action.
You’ve inspired me to download my local weather maps and forecasts, daily as described. It’s something of a hassle to do map by map, but with Apple Automator, two clicks and I have the all the maps on a single, dated pdf, together with the NOAA forecasts, filed in the appropriate folders on my desktop.
Took a while to figure out how to do this. I’m definitely not a computer nerd. I’ve attached a screenshot of the various “Library Actions” I used to create the Automator work flow for maps. I selected the relevant map URLs from
I hope this is helpful.

Tim Sowerby SV White Rose

Screenshot-2023-12-16-at-10.57.16 AM
Tim Sowerby

Thanks for the compliment. I’ve attached a screen shot of a similar work flow for forecasts.

Screenshot-2023-12-17-at-10.39.11 AM

Where can I find weather surface maps for South Africa? I have exhausted my search engine. Thank you.


Thanks for your time and effort. 🙂

Jim Schulz

Does anyone know why the 24h surface forecast maps only show the North American half of the given ocean area rather than the entire area like the 48h – 96h ones? Is there a place to find the entire area for the 24h map? Not a huge deal but scrolling from the latest surface analysis through the forecasts creates a bit of a break in the visual flow.

BTW, here are a couple of links to PDFs from Starpath that folks might find helpful. One for the Atlantic and one for the Pacific. Click on a button to get either the high-resolution image via the internet or request a low-resolution version via Saildocs. Not automated to download everything into one PDF like Tim F gave an example of, but could potentially be turned into an automation?

Michael Jack

Hi, Jim. I don’t know but that is exactly why I wanted the UK Met Office charts because I sail in the North Sea. But as the folks at Sailmail pointed out, I can get the Met Office ones via NOAA as well (the UK Met Office doesn’t allow Saildocs access to its server).

Michael Jack

That is indeed true, John but for those of us who sail in the North Sea and the Baltic as well as the Atlantic, the Met Office charts cover a lot of water further East and North and go almost all the way to St Petersburg and right to the top of Norway:

Jim Schulz

Yes, here’s a screenshot of what I was referencing. Thanks guys!

Michael Jack

Hi, John. What size of area do you choose for the tactical Gribs? For example, I am working on my plan for a sail next year from the North of Denmark to the North of Scotland and then back to around mid-West coast of Norway. My instinct is to download the Gribs for the area bounded by the West Coast of Denmark, the West Coast of the UK (too see what is coming), down to around Dover in the South and a bit North of Bergen in the North. But at the highest resolution the file is way too big. So I have the choice of making either the area smaller or the resolution smaller. Question is, which is the best option?

Michael Jack

Haha yes you did, John and I read that about 5 times and didn’t put 2 and 2 together. You really need to implement some AI to answer those “why can’t I see the wood for the trees” and “my memory is failing me” questions.

Jim Schulz

John, how do you integrate the real-time conditions at your location into your understanding of how the actual weather is evolving compared to the forecast models and charts? Say the forecast shows the wind backing to the northwest at your position at a particular time but it’s actually still coming from the northeast. As things are evolving differently than forecast, how do you integrate that info into your planning? Do you have a systematic way of doing this?

Jim Schulz

Thanks John, your example is a great one. I’ve ordered Frank’s book and look forward to reading it. Despite studying the weather almost daily I feel like I’m still missing some understanding of how troughs and ridges behave. Sounds like his book might help.

Gordan Sket

Hi all,

I’m trying to apply this to the crossing of Atlantic towards west. For that I would like to see surface analysis of Atlantic that includes Cap Verde and Caribbean.

Anybody has a good suggestion of surface analysis for lower North Atlantic?


Terence Thatcher

Thanks for the update. When we went to Polynesia, we used Predict Wind. We could get weather in all latitudes. Next year we will again be sailing south of the US Pacific Ocean Prediction Center maps. Need I again use Predict Wind to get what I need? Someone asked the same question about the south Atlantic. I think you did not have an answer. I would like to follow your advice, but I need to figure out how to get information in lower norther latitudes and perhaps south of the equator. Or do I just stay with Predict Wind? Thanks.

Ken Deemer

I’m curious why you don’t also download wave, current, and sea state forecasts.