Weather Forecasts at Sea – Atlantic

by Adrian on November 17, 2014

After a few days at sea on an ocean crossing, any weather forecast we take with us becomes too old to be of any use. During the crossing we are out of range from all normal communications, so have two ways to receive vital weather information:

SSB is short wave marine radio. We have a good SSB setup on our boat, and can talk to other crews on other boats across vast distances (up to thousands of miles) if the conditions are right and receive small emails containing basic weather reports, computer generated SSBGRIB files predicting wind and pressure systems and synoptic weather faxes. SSB radios are quite technical (you have to do a 5 day long range communications course and be licensed to use it) and can be a bit temperamental as they are prone to atmospheric disturbances reducing quality and hampering download speed. SSB (once installed) is free to use.

Satellite phones work all around the world, are simple to install, easy to use but expensive to run ($1/per minute call charges). They and can only be used like a normal phone to talk to one person at a time. They can be used for data, but like SSB, are limited to very slow reception of small emails (unless you pay many hundreds or thousands of $ per month). Normal yacht systems can be used to access basic mobile web sites and can send very small photo updates and posts to Facebook, twitter, blogs etc.

Our satellite system is an Iridium Go!, with the first ever unlimited satellite data plan, meaning for £85/month we don’t have to worry about how long or how much data we’re using. Satellite data speed is 2.4k – literally a thousand times slower than a typical home broadband system, so the “unlimited” is purely for cost savings – not movie downloads or web browsing. To illustrate how slow slow is, this page would take about 45 minutes to download over our satellite connection. In reality it never would because the satellite drops out and disconnects regularly.


That said, this data plan is great, and will allow us to receive a rich set of weather updates (albeit slowly) and post small blog updates as we cross.

The most useful type of weather nowadays for sailors are computer generated GRIB files, showing increasingly accurate data of wind speeds and pressure systems for any region in the world. GRIBs are the raw output from supercomputer generated climate models, so have not been curated, checked or annotated by human meteorologists. Basically you need to know what you are doing to read them accurately and reliably.

Synoptic charts show weather systems, pressure, fronts and their predicted movement given the raw data and experience of a forecaster. These are generally more accurate for forecasting and fill in more detail.

The weather information we’ll be getting daily:

GRIB files:

Grib weather

Synoptic and analysis charts:

1) Tropical Atlantic Actuals – a detailed meteorologist’s view of the actual weather in the tropical Atlantic. (This is about 86k, but is very detailed and full of raw data. Download my quick guide for help reading these charts)

Tropical Atlantic Actuals

2) Atlantic Surface Wind Analysis – a summarised analysis of the current weather. (about 32k)

Atlantic Surface Wind Analysis

3) 48 hr Atlantic Surface Wind – a forecast for 2 days in advance, so we can see what is predicted to happen (about 34k)

48 hr Atlantic Surface Wind

4) 96 hr Atlantic Surface Wind – a forecast for 4 days in advance, so we can see what is predicted to happen (about 33k)

96 hr Atlantic Surface Wind

5) 24 hr W. Atlantic Wind and Waves – a chart showing wave heights and winds in the western atlantic in the next 24 hours (about 27k)

24 hr W. Atlantic Wind and Waves

Weather sources

NOAA automated ftp

This is an automated and free service that you request by email. Simply send the following email and NOAA’s computer systems will automatically reply with separate emails each containing one of the requested charts.

Send to:
Subject: Weather
Email contents:

cd fax
get PYEA11.TIF
get QDTM10.TIF
get PWAM99.TIF
get PWEE11.TIF
force mime


NOAA automated ftp

Saildocs Automated Grib files

Saildocs have a fully featured automated responder that will fetch and deliver to you by email a grib file for the requested area. The more information that is requested, the larger the attached grib file will be, but the following gives the whole of the Atlantic for 3 days at 12hr intervals and is about 55k in size. It returns surface wind, pressure, precipitation, cloud cover and CAPE data (risk of thunder storms).

Send to:
Subject: Weather Request
Email contents:

send gfs:N11.0,N29.0,W65.0,W11.0|1.0,1.0|0,12..72|PRESS,WIND,APCP,TCDC,CAPE


Saildocs Automated Grib files

You can do a lot with the Saildocs service – you can request Grib files, set up a subscription to send Grib files every day at a specific time, request text weather reports and even request the text from your favourite web sites (such a news site). More info.


Subject: (anything)


See here for a list of good mobile (i.e. very small) sites.


Grib viewers

There are plenty of free GRIB viewers around, but this is a nice one I’ve found. The PredictWind viewer is available on Mac and Windows and can be downloaded and used for free.


There are also very good iOS Grib viewers, my favourite being Weather4D


{ 4 comments… read them below or add one }

Xavier Itzmann March 8, 2015 at 17:04

Hello Adrian,
How has your Iridium Go! experience been? Three questions:
(1) I had originally thought we would go with the “unlimited” £85 monthly plan but the OCENS representative said the $750/1yr/1000 data minutes would probably be a better introduction to the system.
(2) Did you install the outdoor antenna and if so, where?
(3) Go! native e-mail is bound to satellite access and cannot be accessed from shore-based internet connections. Apparently if one wishes anywhere access a third-party e-mail service such as OCENS/XGate ($20/mo.) is required. Thoughts?
Apologies for the longish message, but you have been “out there”.


Adrian March 9, 2015 at 02:28

The unlimited plan can be cancelled and reinstated at any time, which is one big advantage. I easily (slowly) chewed through 200k per day on the Atlantic crossing, which with disconnections and retries took an hour or so per day or connection time. That will use up your 1000 minutes pretty quickly. It also was invaluable being able to test it and play around for however long I wanted without having to worry about minutes – that for me is worth a huge amount.

I’d really recommend the unlimited plan. (The dealer probably doenst get commission on those!)

I didn’t bother with an outdoor antenna, as it worked fine sitting under the sprayhood by the lines and clutches. I actually bought a neat little camera screw thread clamp bracket from ebay and clamped it most of the time on one of the sprayhood frame bars.

I charged it once every 3-4 days. I only had it on whilst using it for data though, as I didn’t need it for anyone calling me.

It did drop connections reasonably often after 30-40k usually, but the email client has a resume feature that picks up where it left off, so a few retries and emails came in and were sent fine. I’m not sure if this is a general sat data issue. I would think it is. This level of sat comms is very old fashioned.

The iridium email apps are just rebadged xgate apps (and about 1 version behind). I discovered an issue with the iridium app and iOS 8 where it wouldn’t use ios’s “open in” for attachment handling (duuh!), whereas the xgate client would, so globaltelsat (who I bought it from) set me up an xgate account for free. I think this costs nothing for them. I think the issue is now resolved in iridium app.

The xgate app does allow web access. I’m sure with a bit of playing around you could also get it working on a normal pop email client.

(That’s important – these email services are pop, not IMAP – ie if you download an email to a device it is removed from the server. So if you have it installed on iPads and iPhones (for backup) emails hitting a device stay on that device.)

One nice feature of the xgate (iridium) email client is the ability for it not to download emails over X kilobytes in size. This allows you to have emails forwarded to it, and see the subject before downloading them.

In practice, I actually haven’t bothered using the web email feature of xgate, as the only emails going to the sat email address were known.

It is slow and was tedious to use, but it did give me connectivity in the middle of the Atlantic and importantly, because it worked on the iPad, was really tangible and easy to use.

Weather4d is my preferred Grib viewer on the iPad and one nice thing it does is it allows for you select your GRIB details and it sends the request via the iridium mail client automatically. This wan nice, and when the reply comes back, you just open in Weather4d and voila, nice interactive gribs.

Lastly, web browsing does not work, regardless of what iridium say. I created a very small test page to test download capability, and it couldn’t even manage this.

I’d love it to work not for browsing, but for being able to download specific web page (weather) gifs directly without all the other rubbish, but alas no.

This was nearly a show stopper for me, but the web to email features of noaa’s ftp system made automated delivery of synoptic charts by email a realistic proposition (as outlined in my post). These and gribs was all the data I needed. Being able to upload blog posts and Facebook updates and small pictures was icing on the cake.



Xavier Itzmann March 9, 2015 at 05:45

Thank you Adrian. I’ve picked up many of your ideas, including roaming flexible panels and the isolation transformer. Great posts!

Yes, I spent all of Sunday researching the issue and had already concluded that the unlimited would be best for ocean crossings, even if US providers charge $50 each time the subscription is turned on. I’ll be sure and check with Globaltelsat. We also have Weather 4D on the iPads. Not surprised the connection breaks every 40k or so, as I’ve read the connection breaks with every satellite handoff, i.e., every handful of minutes or so. POP mail? Heh. So 1994!

We’re off from Ft Lauderdale to Newport in late April/early May and immediately after, weather permitting, off to Portugal. Cheers, and regards to the Girl,


Paul November 17, 2014 at 13:47

Thanks for the great info! Really enjoy these types of posts along with info regarding boat modifications and preparations for journies! So much to learn!! Safe travels and fair winds.


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