How do we get weather information when offshore?

Great sailors have in the past circumnavigated our planet by reading the clouds and relying on typical weather patterns. While this knowledge is still valuable, it is by all means good seamanship to have a proper weather forecast. But how to get a proper weather forecast in the middle of the Atlantic? There are in fact several ways to get weather forecasts while offshore, i.e. without access to regular internet.

First, through our Navtex, which receives weather and other navigational information provided via the Global Maritime Distress and Safety System (GMDSS). This works over radio frequencies (518 kHz) with a typical range of 250 nm from the emitting land station. This is not sufficient for an Atlantic crossing and, anyway, doesn’t work on Naïma right now.

Second, with the help of a HF radio (shortwave). Broadcasts (e.g. BBC) or shortwave weather faxes can be received halfway around the globe, although this may require a bit of experience (we are still learning). For the latter we connect our SSB radio (i.e. shortwave) to our board computer (Mr. Newton), tune into the right frequency at the right time and then use specialized software (e.g. SeaTTY) that converts the radio signal into a weather map – just like dialing into the internet in former times using a modem, just through air. Many boats have a so-called Pactor modem, which enables even more sophisticated data exchange via the SBB radio, including emails and weather data. Unfortunately, we don’t have a Pactor modem and receiving weather faxes has so far not worked properly for us. We hope to get this working in the future.

Third, via satellite. We just bought an Iridium GO! satellite phone, which has a worldwide coverage. It is much more a  plug-and-play type of device than an HF radio, which is also what we wanted in case of emergencies. On top of voice calls it provides us with a (very very slow) data connection. Accessing the internet is almost impossible, but we can send and receive text emails, and, more importantly, get GRIB files.

GRIB files contain grid based weather data such as wind speed, wave height, pressure, temperature, and can be displayed as shown in the picture above. This way we know what is coming, although weather forecasts may be wrong as well. We display GRIB files on Mr. Newton using the fantastic free software Zygrib. We also currently try out Predictwind., which also provides weather routing, i.e. it helps you to plan the optimal route giving your destination and the weather forecast. These are the dotted lines you see in the picture.

Hope you enjoy this post despite its geekiness… sailing gets a bit geeky at times…


3 thoughts on “How do we get weather information when offshore?

    1. With all your experience, I am sure you would have learned all this stuff in half the time it took us… besides, we’ll call for your help when we will reach Dutch waters… navigation there is probably a bit more tricky than on the Atlantic…

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