Strategic Weather Analysis—Hardware and Software

In the last chapter I introduced the concept of strategic weather analysis as an addition to the tactical version that most cruisers do, so if you missed that, please read it now.

In this chapter, and the next three, I'm going to get down into the actual details of how I receive and analyze weather on a day-to-day basis to plan our cruises as much as two weeks out. A system I have developed over 25 years of voyaging that I have recently updated, using the latest tools, over this summer's cruise to remote places.

First off, let's look at the gear and software I use.

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Jordan Bettis

Regarding your point, made in an earlier article, and again here, about precipitation: a potentially even more useful indicator of severe weather is CAPE (Convective Available Potential Energy). zyGrib can display it. I’ve not seen it in many other grib viewers.

zyGrib is more steak than sizzle, I admit. It was developed by engineers without the help of graphic designers. That makes it more “nerdy” perhaps, but I can ignore what it looks like. It’s a very powerful tool.

Jordan Bettis

To be clear I said CAPE is more useful for identifying severe weather. There’s lots of non-severe weather that comes with precipitation.

Consider a weak cold front with rain showers and 20 kt gusts, compared to a cold front with of 50+ knot gusts, heavy lightening, driving rain, perhaps hail and supercells. The difference is usually the amount of CAPE. The former wouldn’t cause me to change my sailing plans but the latter is something I would prefer to avoid, so telling the difference between the two is very useful.

Sounds like you’re happy with LuckGrib. I would point out that your one complaint: that it doesn’t display H and L markers on local pressure maxima and minima. I can report that zyGrib can do this.

Pete Dubler

CAPE is now in PredictWind Offshore app with thIs week’s update.

Marc Dacey

I must say, this is a pretty damn informative thread, not for the contention of the candidates for “most appropriate service”, which is always going to be a matter of taste and need, but to illustrate how the choice of download device, OS and file serving utility are closely linked and drive, to a degree, one’s options.

An added mix is the computational/predictive models on which the forecasts are based. A Canadian meterologist reported a couple of days ago how the U.S. models (GFS?) did not accurately predict Hurricane Irma’s track to the west side of Florida, but the European ones did to a better degree, and how this was causing consternation in her field. So I grasp why “what model does the app use?” would also enter into the decision-making. Me, I’m still reading the 500 MB book, which is worth it, but it’s like a uni course of the non-fluffy kind to wade through the concepts presented.

Marc Dacey

Well, I wasn’t really giving my own opinion but quoting a CBC meteorologist, Johanna Wagstaff. I concur 100 miles is pretty tight for five days. It makes me wonder why people who take Caribbean vacations in hurricane season get off complaining about having to stand around and wait. They could have bought insurance and they could have gotten on a plane. When Irma was still hours from Barbuda, it was pretty clear who was going to catch it. This ability to read the weather must surely play into decisions to go to sea under these circumstances. (I’ve already had this debate with Andy S. on Facebook). I’m wondering if you’ve had to use your weather knowledge to make that decision to stay put in a hurricane hole or to put to sea to get a couple of hundred miles in the right direction.

Pete Dubler

How quickly would you like to see Gust in PredictWind? Turns out it is in last week’s release as well. There are a good number of new features including being able to vary the speed of the running of the gribs displays over time. I too, being old school and having completed the Starpath trainer over a decade ago and having taught meteorology, would enjoy seeing the 500mb data in PredictWind but alas I think too many of today’s sailors are clueless about how to use it. I am surprised how few sailors I have met in the last two years of cruising the Caribbean full time have taken the time to learn the science of meteorology. Most just want to know “What Chris says” and some will look at a gribs or two. PredictWind seems to me, having used it for a few years now, as a good tool to help the cruising masses digest more data easily and get a reasonable view of the conditions over several days on their ipad or PCs. The Pro subscription satisfies my needs for lots of data (but I still look at 500mb faxes).

Charles L Starke

I just downloaded LuckGrib and it look s excellent. LuckGrib can download CAPE. Can you describe how and when to use CAPE, and what to look for? Thanks!
Best wishes,
Charles Starke
s/v Dawnpiper

Jordan Bettis

CAPE is a measure of how unstable the atmosphere is. The more unstable the atmosphere is, the more convection you get. With small amounts of instability you git little fluffy cumulus clouds, with a little more cumulonimbus will start to form and you’ll get rain and gusts. As the amount of instability increases you’ll get strong squalls, lightening, hail, supercells (which cause tornados), microbursts, etc.

When a front is approaching, I like to see less than 1000 J/kg of CAPE in it, and I get concerned when I see more than 2000 J/kg. For reference these are the Storm Prediction Center values:

As John says in the sibling, convection isn’t everything. When it comes to the danger posed by weather at sea a primary concern is sustained surface level winds because they will have the most effect on sea state. Convection is a small contributor to sea state. Surface winds are driven by surface pressure gradients, so what you don’t want to see is tightly squeezed together isobars on the surface analysis, especially not ones with straight lines.

If this isn’t entertaining enough there’s another thing to consider with convection: wind shear. Wind shear occurs when air at different levels in the atmosphere blow in different directions. If you’ve ever seen fall streaks from cirrus clouds you’ve seen wind shear. When you have lots of wind shear you can have severe weather even with small CAPE. Here’s a diagram showing the relationship:

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In zyGrib, you can investigate wind shear with a soundings diagram. To get it, you have to first download all the GFS altitude packages (second tab on the download menu). Then right click on the map where you want to see the soundings and select SkewT-LogP DIagram.


Wow! Thanks!

Just bought LuckGrib, opened the program, downloaded a grib with parameters I selected, and am enjoying the display. It was a snap to get started. Very intuitive. Now I will read manual/instructions to get more out of LuckGrib. Then LuckGrib can serve as an aid to self study and a weather course.

I have been using OpenCpn with the grib plug-in to view grib files I receive from sailmail. I had not gone to the trouble of setting up a dedicated grib viewer. LuckGrib appears far more powerful and was vastly easier to set-up. It makes acquiring the grib files a snap.

Thankfully I bought a refurbished MacBook Pro a couple of months ago in order to explore MacOS computing, so I was ready for LuckGrib when I read your article. LuckGrib requires OS X 10.11 or later (I had to upgrade but machine was fine). If someone is just getting started with grib file weather, even if they are a PC user like myself, I would suggest getting a Mac capable of running LuckGrib as the cost of LuckGrib and the hardware is well worth the savings in aggravation and technical learning required with alternatives.

iñigo ortiz de urbina

Hi John
Have you tried Squid? ( I think it offers the most complete bunch of weather info in a very friendly interface ( includind sat images, observations, scat winds and of course a variety od models) subscription options are very attractive. It is in continuous development and is a standard tool for offshore racers now thanks to its user friendliness and integration with routing softwares. It also allows email requests.
Best regards

iñigo ortiz de urbina

I see your point, but maybe it deserves a try. For me its greatest advantage is that allows a straightforward overlay of sat images, grib data, scat winds and observations, which is very useful for assessing the models against “real data”, something not available with other viewers and still a bit cumbersome with Expedition or Adrena for instance. I used to georeference images in Expedition (in the case of sat pictures pre-processed with geosarsignal), but much easier with squid now. It also includes a routing module (only online) but for that Expedition and Adrena give much more powerful tools yet.
In any case I still use saildocs extensively specially with an iridium connection, using lists of links to specific met products, but when inmarsat fleet is available (frequent in offshore racing these days) squid saves a lot of time.


Re access to ECMWF: for several years I have used the paid service “Wetterwelt” from Kiel, Germany. They provide ECMWF with some secret sauce added. Currently it’s EUR 99/year including 19% German sales tax for the service which includes the software.
A screenshot:
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It meets your requirements 1 and 4 but not 2 and 3. I briefly looked at Viewfax years ago and have been using zyGrib (my zyGrib doesn’t display H and L; I must have an older version). Of the three, I prefer Wetterwelt for its information display and useability (but wouldn’t call useability excellent).
A feature that I like and sometimes use is to mark a route by clicking waypoints onto the chart and then add information like start time and average speed. After that a yellow marker shows up moving along the route in sync with the forecast date and time (the marker jumps as you click through the forecasts).
The shading in the screenshot is for gusts but that can be customized (there was some bad weather here yesterday and the route is older. I wasn’t at sea yesterday).
The available data is:
Surface wind direction
Surface wind speed
Wave height
Swell direction
Wave period
Surface pressure
Temperature (air)
Don’t know if their grib files will open OK in another viewer.
I have “the 500MB book” on my shelf and made it through the first 10 pages so far. Each fall, I again resolve to work through it this coming winter.
I wouldn’t consider using a routing tool unless I were a race navigator, for which I have no plans.
I like PC software vs. an app. I don’t like to see tablets being used widely because it directs development resources in the wrong direction (my opinion, and I’m not 80 years old either) but of course cannot help it. So I own a tablet as a cheap backup for the navigation software and computer and for reading magazines on the sofa (consuming, as you said). Mac software rules me out, at least so far. But I would much rather use a Mac computer than a tablet, either iOS or Android.
I guess I will stick with zyGrib and not try Viewfax again as I already have used zyGrib, on and off, for several years. But I will get a current version.
Re integrated know-all, have-all services I think that, to be safe and not suffer unnecessary, you have to “learn weather”. You can’t buy yourself free from it. And learning weather is a slow process. After 10 years of owning the boat, I am at best intermediate.

1. Why is H and L important? Lows are much smaller and the wind arrows tell for sure (not defending my current SW, just curious).
2. With 500MB display, how are the wind arrows for surface and 500MB level separated/identified? (maybe if I had finished “the book” I wouldn’t ask this)
3. I always thought that Gribs are for shorter term immediate route planning and NOAA or UK Met Office meteorologist-produced weather charts for general outlook and overview (strategic weather analysis). What made you depart from that strategy? Weather charts can be pulled by UUPlus. If everyone did what you are doing (use Gribs exclusively), we wouldn’t need meteorologists anymore (or only as weather model software developers). That doesn’t sound like a good idea. You also said you need weather in gribs to see the rain to know where the fronts are. But in a classic weather chart the fronts are drawn way more clearly and by an expert. It seems like you are trying to do with gribs what used to be done with weather charts. Why bother? Is it because gribs are available further out that meteorologist-produced weather maps?
4. You say you use UUPlus to “download” gribs and that you have asked UUPlus to include missing parameters (data points in the grib?). I don’t understand. Do you use the file-getting feature of UUPlus or is there now a grib-request feature built into UUPlus? For our long passages we had to request gribs to be sent twice a day via email. That was with Wetterwelt via a completely manual process. zyGrib used to have a feature on their web page to have a specific file emailed to you for up to 2 weeks but it was dropped long ago.
Could you detail a little more on the actual process of getting the file/data with the 3 solutions you describe? Or is that coming in another post?

Jordan Bettis

> (my zyGrib doesn’t display H and L; I must have an older version).

Go to the Isolines menu and check the “Pressure Low High” checkbox. I have version 6.2.3.

> 1. Why is H and L important?

You’re right that you can usually guess where the middle of the (anti)cyclone is by looking at the isobars and wind arrows, but why guess at it when you don’t have to?

> 2. With 500MB display, how are the wind arrows for surface and 500MB level separated/identified?

In zyGrib the wind arrows are only for the surface, but you can get see winds aloft by right clicking on the map and selecting “SkewP-LogP Diagram”

> 3. I always thought that Gribs are for shorter term immediate route planning and NOAA or UK Met Office meteorologist-produced weather charts for general outlook and overview (strategic weather analysis).

Meteorologist-created data is always much better than a GRIB. The advantage of GRIBs is that the forecast is updated as often as the model runs, and there’s much more detail than is usually available in official forecasts.

Nick Olson (PredictWind)

Hi John,

As you specifically mention PredictWind in this article I would like to address some of your opinions. We acknowledge that everyone has their own way of using the weather options available, just like we all have our preferences on which boat designer/ sailmaker/ navigation software or deck hardware is best. Our goal is to provide and deliver the very best forecast data so sailors can make safe and informed decisions. We are all experienced offshore sailors ourselves and understand the requirements when sailing offshore, be it 1 day or 30 days at sea.

Weather Models
– Weather models are not “all the same under the hood”. We have expertise at running various weather models so have in depth knowledge in this area.
– The ECMWF consistently gets the highest rating score. It is scientifically proven to be the best global model.
– No single model is every correct 100% of the time, none. This is why PredictWind makes it very easy to compare 4 top models including the ECMWF and GFS
– Comparing multiple models is common practice with all top navigators including Stan Honey, and all experienced navigators and meteorologists we have contact with.
– We actually offer the ECMWF global GRIBs for Free on land based internet connections. This applies to all our models.
-The Offshore App is free and can be used on Mac, PC, iOS and Android devices.

Weather Routing

-Manually doing weather routing is very time consuming, and error prone There is a lot of “fuss and fret” with this method, and unlikely to give you the best results. Why not make it fast and easy? Experienced sailor or not, most can see this routing tool as essential once they have experienced the benefits for themselves.
– Possibly I think you miss the main point of the PredictWind weather routing service. The cloud based routing delivers the wind/wave/current from 4 models, in less than 1% of the equivalent GRIB file size. The data is also presented relative to your route, and the GRIB files.
– The speed and simplicity is enough to convince most cruising sailors of the benefits The data download size (9kb maximum) for 4 atmospheric weather models, 2 wave models and 1 current model is appealing to all sailors. The results are in graph and table view and easily compared in a few minutes.
– Yes, setting up Polars is very important to any weather routing . Most cruisers setup the Sail polars feature where they manually enter in their own upwind/reaching/downwind speed specifically for their boat.
– Polar errors affect manual routing or the PredictWind routing in the same manner.
– The departure planning tool calculates 4 routes, spaced 1 day apart and will summarize the results. This tool helps sailor being caught out, like your example of being caught out at sea by the passage ending up being a day or two slower.
– Good seamanship is not getting caught out in bad weather. The weather routing & departure planning help simplify that process.

PredictWind Offshore

– It is nice to see you like the simplicity of the Direct Download via Iridium Go in the Offshore App.
– It is a very streamlined process versus email requests, no file saving and transferring, a real time saver. It works the same with a redport optimizer to enable any satellite connection to do direct downloads. We have recently added the Gust and Cape variables in response to customer feedback, and may also add the 500mb layer if we get sufficient customer requests.
– The “H” and “L” feature would be a nice feature, but I have taught my kids to distinguish between high and lows without it.
– Our goal is to make available the best quality weather data, with powerful tools to present the data (weather routing & departure planning) than can be used by all user levels.
– The Offshore App is available on Mac, PC, iOS and Android. So no need to juggle between platforms.

michael poirier

I just sent a small question to Craig from LuckGrib (at 11PM Friday night) and he replied in less than an hour!

Now that is service!

Craig McPheeters

Hi John,

Thank you for mentioning LuckGrib, I appreciate it. As you spend more time with the software, please let me know if you have any questions or suggestions.

Having read over the comments I would like to add a couple of points.

I have used ViewFax and zyGrib in the past, and generally liked them. The more options sailors have to download and view weather forecasts the better, in my opinion. I have had friends who have used PredictWind and liked it. My experience is that everybody who has used the other software and then used LuckGrib has preferred LuckGrib (If somebody doesn’t have this experience please email me as I would love to hear why.) Of course LuckGrib doesn’t do automated weather routing, and I generally agree with your reservations here, but if this was important to someone then they would need to look for additional software.

CAPE has been mentioned several times. LuckGrib does indeed support downloading CAPE from several of the models it supports. It also supports CIN (convective inhibition) and LI (surface lifted index) which are all convection related. If anybody is interested in doing some research to see how these parameters relate and which ones are most useful and how they can be used I would like to hear about it. I have used the wind/pressure/rain combination with success in my sailing so far.

On the discussion of the various models – its true that ECMWF seems to be the current champion these days, having higher skill scores on average than the other models, and that LuckGrib does not provide this model. Its my understanding that Hurricanes are difficult to forecast in detail, i.e. locating its center with extreme accuracy. I suspect that for sailors, any of the global models would have provided sufficient information to make your decisions – i.e. if I see a forecast with a hurricane passing anywhere near to me 6 days from now, I need to start planning, regardless of which side of the track I’m forecast to be on, etc.

For hurricanes in North America, LuckGrib is able to provide access to several of the models that NOAA provides (for free), some of which are updated every hour. For example, HRRR is a high resolution (3km) model updated every hour and it incorporates high resolution radar imagery and so tends to be very accurate (but only for the 18 hours of forecast data it provides.) As an aside, HRRR would be an excellent resource for North American sailors to use when day sailing – high resolution and hourly updates.

On the display of H and L for the sea level pressure – this has been generalized, so you are able to display the local maxima of wind speed or rain if you want. If you are viewing wind gusts, you could have a marker show the maximum wind gust location. H and L are simply local minima and maxima, LuckGrib allows you to view these for any of the parameters it can view. Ok, that’s perhaps a bit nerdy, but I thought it was cool.

A short note on routing. LuckGrib does allow some rudimentary routing workflows. You can measure distances on the map for example, as well as construct a route, create named ‘vessels’ and plot their tracks and have them follow a route. This last feature was very handy in my passage from New Zealand to Hawaii (50 days), both in departure planning as well as to make it easy to quickly see where I was while on passage, along with seeing the wind angles and distances as I look through a downloaded weather forecast. I could manually optimize my route for the next day or two, based on the latest weather download. Its not automatic – it is somewhat like providing an electronic version of graph paper where you can go through course change experiments. This was also useful for tracking several companion boats as we all made progress along our passages.

Nick from PredictWind mentioned that they offer four models. Cool. I do find comparing weather models to each other useful, although more in the departure planning scenario than while on passage. PW appear to offer GFS and ECMWF, each in two flavors, native and with secret sauce added. LuckGrib offers GFS, the Canadian GDPS along with two ensemble models (CMC and GEFS.) That’s pretty good coverage when doing departure planning. LuckGrib currently provides 31 models. In addition to the four already mentioned, there are three global ocean models (two wave models, and RTOFS which offers ocean current/temp at 1/12°) The remainder of the 31 are regional models, with good coverage for North America and Europe (two 0.1° European wave models for example.)

For anybody reading this far into this comment – if you have a Mac and are interested in weather, spending the $20 for LuckGrib should be a pretty easy decision (all of the data is free! No subscriptions! Best in class graphics!)

Nick Olson (PredictWind)

Hi All,

I would like clarify Craigs comment and I think John has mentioned this too. PredictWind does NOT add “secret sauce” to the ECMWF or GFS weather models to produce our proprietary global model outputs. The PWG and PWE forecasts area full global model calculation. Before a weather model is run it has an Initial Conditions file entered in to it. I think this is where the confusion can come from. We do use the ECMWF and NCEP (GFS) initial conditions files. To produce an initial conditions file is a big deal, but it is not a forecast, it is the snapshot in time for that day.
Once you have the initial conditions you add in a forecast model along with a huge amount of computing power, after this you get your global forecast model. For us this is PWG and PWE global models.
PredictWind ‘buys’ the computing power to do this for each model run, something that allows us to do something which is normally the domain of government agencies, being a private company we do it more efficiently. Many top navigators use our model outputs as they are very good and often times do a better job for them.
We actually ditched the GEM(CMC) model after years of complaints about its inaccuracy (anecdotal of course), this is when we replaced it with the ECMWF at the same time changing our initial conditions source for the PWE to ECMWF.
You can read more on this here

Dick Stevenson

Hi John and all,
Much that has been written here is way above me, I suspect, in part, as I have had spotty internet this last decade or more and when I do have it, it is pay as you go, which inhibits poking around and exploring. So, I am personally unfamiliar with these routing programs that are being discussed. That said, I can’t imagine leaving passage/departure decisions up to a computer program. Working the weather data out as far as possible, working with your likely day’s mileage, anticipating the pros and cons of going above or below a great circle route, anticipating the effect of a low traveling faster or going farther north, etc. etc. puts me into the rhythm of a passage and facilitates making good decisions when things start to go a bit different than predicted, always likely.
My best, Dick Stevenson, s/v Alchemy

Alan Trimble

I am slowly working through the details of actually using much of the technology discussed in the postings and responses. While I really appreciate the integration and simplicity of PredictWind’s Offshore App, I also use LuckGrib while in WiFi range. It would be lovely for someone to detail the recipe of using UUPLUS with the GO! to download GRIBs offshore for display in LuckGrib… someone here must have done this successfully.

Glen Doyon

I too have been reading all of the chapters in this book. I’m new at using some of this technology but trying to figure it out. I downloaded LuckGrib (which is NOT free, as I think someone mentioned, and $20 as I think it’s author mentioned) and I’ve got an Iridium 9505 with which I can download GRIB files to view with ViewFax on the boat’s PC. But Ive used LuckGrib to view downloaded weather files and it seems so much better….BUTTTT, I’ve only been able to do this in a wifi environment. I cannot find a 9 pin to USB cable that works with the sat phone that my MAC can see!!! All the cables I’ve tried (four, and I’m pretty sick of it) only seem to work with Windows. LuckGrib does not run on Windows (and I’d rather use my Mac anyway. Any suggestions?

Glen Doyon

I’m using UUplus on both the PC and the Mac. That is a great recommendation, btw. the software is not exactly “Apple intuitive” but the support from John and Jeremy has been nothing if not extraordinary. I’m all sorted out on the PC (which I couldn’t have done without help, as I wouldn’t have understood why ViewFax wouldn’t open the GRIB the first time, for example). Now it’s just a matter of using the software on a daily basis and I’ll get it down. That said, both UUplus and LuckGrib are working just fine on the Mac. The problem is I can’t find a cable that talks to both the Mac and the satphone. All the cables seem to have drivers for PC’s only. Any help with that? Thanks.

Pete Dubler

Hi John,
I’ve been re-reading this book over the last couple of days. I appreciate your very experienced perspective. I think we were both weaned on raw surface and 500mb faxes on curly thermal paper. That experience never leaves us. I think though that the majority of cruising sailors today lack the kind of meteorology training and study we felt we needed many years ago. The “weather” discussions I hear at anchorage these days seems to be about “What Chris said”. I don’t hear people saying things like “did you see the omega block developing that will likely stall this system…” or other comments that indicate they have either seem the real weather data or had some understanding of what they saw. Now I don’t want to slight other sailors but this seems to be today’s, just add water, sailing community in oday’s instant information world where thinking for one’s self is rarely required. This of course goes to the first article in this series in which you share the timeless advice hat the only one responsible for the weather forecast is the captain of the boat. I agree with your comments on gribs viewing tools but I have a different perspective on where the PredictWind toolset fits in. Here is my perspective, for what it’s worth. 1) The routing and departure animation features in PredictWind are huge time savers. We managed to tune the polars derating for our boat after a few crossings to where these tools are very useful for us. Running departure scenarios first on 24 or 48 hour intervals (four departure time runs per download) then having the interval once he best window as found, and repeating a few times gives us great insights into to expected weather. This is also a huge time saver for me when planning passages. 2) I believe you wrote that you have not benefitted from the hi res downloads in PredictWind in the areas where you have been cruising. When I have used these in the Caribbean, I found them to offer a lot more detailed and accurate prediction particularly near land as they seem to consider more of the local effects such as downs open winds on steep shores. I have found the ECMWF hi res models to be best in this regard. Unfortunately, as you know, these hi res files are big and often too big for Iridium downloads. When we sail where there is no hi res dataset available, I really miss them. 3) All together, I see the PredictWind Offshore tools with the Pro subscription address a potential audience that wants to develop their understanding of the weather facing them but does not have that higher level of meteorology study that you and I grew up with. That said, I find the tools fulfill my needs though I join you in wanting to see the 500mb data too; and 4) I remain impressed with the continued work to enhance the PredictWind Offshore tools. This is not a one-hit wonder. We keep getting better and more helpful features and datasets from PredictWind. Of course, it is up to sailors to gain the knowledge of how to use or interpret the addition data that is available.
Keep up the great work John. I find myself constantly recommending your site to sailors who seem to want to learn (as opposed to those who just want to be handed “the answer”).

Eric Klem

Hi John,

I tend to steer clear of weather discussions as I am not that knowledgeable about the subject but your comment about routing programs got me thinking. Your concern over taking the output of the program at face value is completely justified.

What I think is interesting with using routing is if you can run a sensitivity analysis. Just like weather forecasters look at “spaghetti plots”, you can look at what happens if the boat speed is slower or faster than what you have programmed in with your “nominal” polar that you create. By looking at these outputs, you can see what your margin is and what the consequences are of being a bit slow or fast (for example, you may find that there is one section where it is worth motoring for a few hours if your speed average drops even a tiny bit). You can obviously do this all manually but a computer can do it more quickly so you can run more scenarios and it often displays information in a better way.

Weather and routing programs are all changing relatively quickly and it has been a few years since I have done a passage where I have messed with this stuff so I can’t speak to what the automated versus manual capabilities are in current software platforms. What I do know is that I do sensitivity analysis regularly in my job from simple stuff like tolerance analysis in Enventive to much more complicated dynamic modeling in different programs and this analysis almost always is more informative than the nominal analysis on its own.



Hi Jon,
I’m new here – I only wish I had found you earlier. What an amazing mine of information!
We have been full time live-aboards for 10 years but in rather less “rugged” waters than you and many of your other readers sail upon. We have spent all our time in the Mediterranean. The weather (at least in the summer) is reasonably predictable, the sea is warm, the distances are usually short and the cell phone network is close to ubiquitous. That said, the Med can be vicious and needs to be treated with great respect. The great god Poseidon is not a forgiving deity.
I have been reading with great interest, your weather chapters. I hope you won’t mind me giving my perspective as one of the “modern cruisers” referred to rather disparagingly. I don’t have any formal weather training although I do have enough physics and engineering to understand your arguments, what a weather model is and what its limitations are.
Most days, I only need to know what the weather will be like today and the following night so that:
I have a gentle passage to a safe anchorage or mooring and a good night sleep.
Or know that I’m better off staying put and possibly battening down the hatches.
Or I change my plans and go somewhere else.
I have seldom found that meteorologist-generated forecasts have been useful to me and are often seriously misleading – I have often been warned of high winds and/or thunder storms and then have had a clear blue sky and gentle breezes all day (although never the reverse). I guess this because they always forecast the worst anywhere in a large area and that is often a long way from me. In contrast, I have found, GRIB based forecasts to be much more reliable for a couple of days – even the Mistral, the Meltemi and usually the Bora seem well predicted.
In the early days, I used raw low-res GRIB files and did my best to figure out the all important island and mountain-valley effects – with limited success. PredictWind with its high resolution accounting for terrain, was a revelation. Many times it has warned me of narrow high-velocity, streams of air – some of which might have been predictable with careful examination of the chart or Google Earth and others that were not. Several times I have warned other skippers in a Greek town quay or anchorage of a coming local blow which was predicted by nobody else. I find PredictWind much quicker and more reliable for this than doing it manually. The dual display of two different initialisations of the same model helps me to judge how likely the forecast is to pan out as predicted. In the Med, rain nearly always falls from cumulonimbus often with associated squalls – so I always check for rain predictions and assume that they have wind and lightening. My expectation was they would just be indications but to my surprise – at least for 24 hours – PredictWind is amazingly good at pinpointing them.

Occasionally, we undertake a passage of 2-3 days. On those occasions, I do a manual process similar to what you have described. I am eagerly awaiting your forthcoming chapters for more ideas. In the past, I tried to guess where I would be when I would be there and what the weather would be at that point. I then fed this into an attempt at manual weather routing and departure planning. This was moderately successful but very laborious. I have found the weather routing and particularly the departure planning in Predict Wind to be a huge help with this as it takes most of the drudgery out. I never rely totally on it of course but always check by following the suggestions on-screen while looking at the wider picture to ensure that it is not just-missing a larger weather feature that may well hit us and also to ensure it is not taking me through a thunder storm.

I see that you recommend writing a text forecast – and I absolutely agree. I have always done this and written it in the log. It concentrates the mind and clarifies the thoughts very well and it gives guidance for the admiral when she is on the helm (or even when deciding when and what to cook) and refreshes my own ageing memory.

I can absolutely understand why you advocate a more manual approach for the long passages and dangerous waters that you sail. What do you think of my approach for the shorter kinder passages that I do?

Jeff McKay

Wondering if you have any comment on “GRIB Explorer Plus” by OCENS? I am looking at it because I bought my Iridium Go/service from them. And my general comment on this is I wish somebody would write “GRIB Analysis For Dummies”, because I really need it. I don’t even know what you are talking about with terms like “500mb”, “CAPE”, etc. (well I do now since I’ve googled it) but then I have to choose which model, and which data source, with absolutely no guidance from any GRIB software I have seen) – it is really intimidating.


Hi John and Colin. Have very much enjoyed your website since becoming a member earlier this year. Also enjoyed meeting Colin at East River Marine this summer. Here’s what caught my attention in this article:) Where do you get off using an expression like “sturm und drang”. Do you even know what that means?
S/V Snowdrift


Hi John,

one nice feature of View Fax is the little boat which moves together with the time frame of the Grib model, indicating were you ought to be , approximately. I always find that quite useful! Saves me having to imagine where I will be in 3 days time.

Are you aware of any other grib viewer that does that?


Cory Hall

John, have you an analysis of all the monthly subscriptions you pay for in regards to navigation and weather? I haven’t added them up but it feels like there are a lot of monthly charges/subscriptions for things. We are preparing to do some extended sailing and I have been contemplating signing up for some of the things like iridium go, a charting program such as navionics etc. but it seems like its getting out of reach when on a budget.



Andre Langevin

I have tried to illustrate how the different equipment/application presented in this book would fit on my boat where i am already riding the devil with a Windows navigation computer running TimeZero linked to the Furuno Navnet, radar, chartplotter, autopilot. Last year i purchased an old Sirius XM weather receiver for 100 US and it displays nice wind, fronts, lighting on the chartplotter but this is just valuable for coastal cruising. I already have a WeatherFAX/Navtext and an ICOM 802 SSB with pactor. Using Winlink for the moment. So i plan to add an Iridium GO and engage with Sailmail and perhaps also PredictWind…

Comments are welcomed. An image is worth a thousand words…

Robert McDowell

Helping my daughter’s engineering class launch a high altitude weather balloon. I found this site that is really fun to play with and may even have some useful properties!


John Reardon

Do you have a primer on how to calculate and tweak polars? There are none published for my vessel.

I’ve been playing with OpenCPN lately and downloaded some GRIBS into their weather module. Any comments on the OpenCPN viewer?

Michael Lambert

I’ve just started playing with TZ on boot camp, but have previously enjoyed getting to know luckgrib, which lives in the other side of a reboot. So I wonder what you think of the weather program in TZ? If it worked well enough that would certainly be convenient.

Michael Lambert

Thanks so much John, I’ve played with it on an iPad but at the time I didn’t like it like I do luckgrib, but I’ll take a look at the windows version, since it would be great to simplify sharing of waypoints etc.

John Deakin

As always so much good information and experience to digest. Thank you all.
It may be of interest to anyone wanting to try out LuckGrib ( which l recommend) that your Mac OS version may be a limiting factor.
Having tried the 14 day free trail on my iPhone l thought splash out and buy the version for my trusty old MacbookPro late 2012.
Ok stop laughing 😝 everyone, at least l can take mine apart and insert memory etc 👍
But, a big but, will my present OS run the latest version on the OS App Store.
It’s indicating that it needs Big Sur to download. Not to be put off l tried on one of my old Mac Pro towers running High Sierra again nope it wouldn’t download.
At this point l must point out l’m retired from the world of video editing hence my trusty Macs (vintage!)
I’ve been in touch with Craig McPheeters who has been very helpful, credit to the man and good YouTube videos to watch and evaluate the program.
If anyone has recently downloaded LuckGrib onto a Mac what OS were you running at the time and did you notice on the App Store what OS requirements did it need.