WATCHOUT Wind and weather data

01 Oct 2022 The Navigator

There is so much information now available on the Internet, compared to the single forecasts of even 20 years ago. The big question is, however, which source should you trust? Cdre Nick Nash, FNI, looks at available data sources for weather and route planning and explains why a simple set of spreadsheets can help him get a better handle on the wind

As a Master of a 145,000 GRT large passenger cruise liner, weather information, particularly wind forecasts, is vital to our safe and efficient harbour manoeuvres and transits – we have a 13,800m2 sail area, after all. There is so much information now available on the Internet, compared to the single forecasts of even 20 years ago. Today, there are no less than eleven global weather models, of which the two best known are the European Centre for Medium-Range Weather Forecast (ECMWF) model and the National Weather Service’s Global Forecast System (GFS) model.

The big question is, which one do you trust, particularly, or more annoyingly, when they disagree – which is quite often? I tend to try and use a ‘Government’ sponsored website, if available, such as the UK Met Office, for Norway and, of course, NOAA for the USA. Their accuracy does vary, but in complaining about this, a Master of a large vessel must take into account the fact that these weather forecasts are all intended for a ten-metre height, whereas most large cruise liners have their anemometer at least 50m above sea level.

Writing down the wind
I have found the best way to determine the accuracy of the forecast for each particular port is by making a spreadsheet of ‘forecast wind’ and ‘actual wind’ at key waypoints on the approach – outside, pilot area, inside and berth wind.

A spreadsheet like this, built up over numerous calls, gives the Master confidence in the forecast model they tend to use. A refinement could be to include a column noting the different forecast models.

A further issue that a Master can face is the afternoon ‘sea breeze’. This is rarely forecasted and a day forecast for, say, Marseille gives a wind forecast of 10-15 knots throughout the day (Windfinder) with a slight increase in the afternoon to, say, 18 knots. In reality, the SW on-shore wind can easily increase to 30-35 knots from 3pm to 7pm. Again, I have an Excel spreadsheet that tries to predict when this afternoon sea breeze will kick in by recording weather, pressure and noon temperatures, alongside morning wind speeds.

There is a feeling, particularly among older seafarers, that the Master’s decision-making has been diluted by shore communications and the amount of web-based information now available to them. I don’t think this is so. I feel as a Master that I now make betterinformed decisions based on a whole lot more data. The trick is to understand where this data is coming from – its source and how far you can be confident in its accuracy. This is easier with government-sponsored sites,such as the UK Hydrographic Office, UK Met Office, NOAA, MPA (Singapore), Australian Chart Agency, SEMAR (Mexico) etc.

Route planning has become a growth industry. This is no longer a case of a lone second officer drawing course lines on charts laid out on a table tennis table to ensure all the rhumb lines match up at chart changes! Intelligent software can collate, integrate and analyse marine information to support decision-making.

For some companies, the use of a fleet-based operation centre assists this by offering a number of pre-planned routes for the ship’s navigator to choose from, say, from Miami to the Caribbean. These routes will take into consideration elements such as fuel economy, environmental boundaries/ restrictions and possible medical deviations – as well as that all-essential factor: weather.

The Master now has an abundance of information and support available to enable them to plan, depart, transit and arrive safely, on time, environmentally compliant and economically.