Using the Internet for Marine Weather

I often get asked by sailors about where to find the best “free” weather information on the internet, or which web site offers the best information. As anyone who has spent any time looking for such information on line knows, there are many, many sites offering weather information which is displayed or listed in any number of formats. There are web sites provided by government weather services, including U.S. and many other countries. There are web sites provided by media outlets, like The Weather Channel and just about every other commercial television station in the U.S. There are web sites provided by various marine interest groups. And there are web sites provided by private companies. The data can be displayed as text only, charts, graphs, maps, fancy pictures and icons, or some combination of these. In short, there is enough weather information on the internet to make one’s head spin!

WWWSo how does one evaluate the information available? First, it is critically important with any one of these sites to make sure that you know what type of data you are looking at, what it’s source is, and how recent the data is. For example, is the data actual, observed data, or data derived from a few known points? Is it observed data, or forecast data? Was it updated within the past few hours, or is it a few days old? The answers to these and other similar questions will give you great insight into how you should rely on or use a particular web site.

There are some web sites that will allow you to input the latitude and longitude of any point and then provide you with information for that point. Chances are this information was not observed directly at that point, but is based on a networkof observing points nearby. The data may be reasonably accurate, or it may not. My point here is not to criticize any given website or type of website, but rather to make sure that users take the time to examine carefully where the data came from, and use the data with the full knowledge of how it was obtained or generated. This will allow you to carefully discriminate between different web sites, giving more credence to those whose data seem more reliable.

Many web sites offer forecast information for many days into the future. Again, it is useful to know what the source of the information is. Forecast information that has been generated or reviewed by a professional meteorologist is likely to be more accurate than information which is derived purely from one of the many mathematical forecast models in use. Often, such model data is presented without any additional analysis at all. Again, this does not mean that the pure model output is necessarily inaccurate on any given day, but as a user, it is important to be aware of the source of the information.

mapIn general, the longer into the future a forecast goes, the less reliable the forecast is likely to be. This makes intuitive sense, and holds for both pure model output and for forecasts generated by meteorologists. This is why it is important to know when the forecast data which you are relying on was generated. If it is a few days old, you would be wise to look for something more recent.

An increasing number of boats now have internet capability while cruising. If you plan to use the internet while you are offshore, it makes sense to explore the many web sites well in advance of any passage, and to make some determinations based on the parameters I have discussed as to which ones will be of greatest use. For most folks, the connection speed offshore is considerably slower than land based broadband connections, so keep this in mind when selecting the site or sites that you plan to use. The most accurate, comprehensive site available will be of little use offshore if it takes too long to load.

Ship internetTo sum up, make sure you know what type of data you are looking at, where it came from, and how recently it was generated. Make sure that the web sites you plan to use will load in a reasonable time at the connection speed you will be using. Look past flashy graphics or data that appear to be available at any location for any time, and make sure that the source of the data meets your criteria.

In a future newsletter I will review some specific web sites which may be useful. In the meantime, explore with a critical eye, and if you have a web site that you would like me to comment on or include in my review, email me at


By Ocean Navigator