Weather data sources

Before going voyaging, most folks try to carefully assess their needs and wants, then plan to meet those needs and wants. I am amazed that many folks fail to anticipate how much their enjoyment of each day will depend on the weather. An actionable (pertinent and reliable) weather forecast is one of the small vessel skipper’s most important decision-making tools. But once you leave the land of Wal-Mart and wi-fi, obtaining weather information you need for decision-making requires specialized tools. We’ll explore some of those tools, and get into some specifics on one of the newer entrants — direct broadcast satellite (DBS), where a receiver and a monthly subscription grant continuously updated weather information.

Of course, there are trade-offs among the various weather products and delivery methods. We’ll consider trade-offs such as bandwidth utilization, reliability of reception, signal coverage, convenience, cost, reliability of forecast, diversity of offerings and versatility of equipment for other purposes.

For many decades, high-frequency (HF) radio has been a mainstay for voice and fax weather reception and general vessel communications. NOAA’s National Weather Service (NWS) broadcasts voice and weatherfax data via Coast Guard transmitters in the U.S. (including transmitters in Alaska and Hawaii) and Guam.

Many other governments broadcast similar voice and fax products over HF radio, covering virtually the entire world.

HF radio
Let’s examine the trade-offs with broadcast weather information via HF radio. Simply tune an inexpensive HF receiver to the desired frequency at the appropriate time to listen to a forecast for your area. Connect the radio to a computer to receive images (weatherfax charts) in addition to voice forecasts.

Each forecast product is transmitted only once during a rotating schedule, and an unlimited number of people can receive the broadcast simultaneously, so bandwidth is used fairly well. But voice and graphics (see “Data types” sidebar) are not the most efficient use of bandwidth, and there’s a limited menu of product offerings. Fortunately, this bandwidth is paid for by the entity transmitting the information, and anyone can receive it free of charge, so there is no ongoing cost to you. However, poor radio propagation or noise can make reception unreliable or the received product unintelligible. Convenience is also an issue, as your equipment must be on and tuned properly at the correct time to receive the broadcast. While most areas are covered and forecasts are prepared by professional meteorologists, the vast geography often necessitates a vague forecast not targeted to the needs of small vessels.

With an HF (SSB/Ham) transceiver, which can transmit as wells as simply receive, on board you have access to all of the above, plus the ability to talk with a weather forecaster or router in some areas, and participate in radio nets, which may offer weather forecasts. While the details of these additional weather sources vary from area to area, the more expensive radio transceiver is more sensitive, making reception of broadcasts detailed above more certain. The transceiver is also more versatile, giving you the ability to communicate with other vessels over great distances, place a phone call via a marine operator, and, especially with the newer DSC-equipped SSB radios, broadcast a distress signal.

With a specialized modem, an HF transceiver and an HF e-mail service provider, you can even request specific weather information via e-mail. While you still have all the capabilities to receive HF broadcast weather, talk and listen on weather nets, etc., as above, obtaining weather products via e-mail brings a new set of trade-offs. Since you are the only one able to receive an e-mail transmission, bandwidth utilization is relatively poor. Newer digital formats, (Vector-based, usually gridded) such as GRIB data, improve bandwidth utilization by getting you more useful data in less time. Reliability of e-mail is excellent due to error correction, but you still need acceptable radio propagation. E-mail offers nearly on-demand convenience, assuming you don’t have to wait in line for the limited bandwidth. Equipment is expensive and service plans vary by provider, though WinLink is free for Hams (and in some areas has a long line of users waiting for their turn over the limited bandwidth). Coverage varies by provider but is available nearly anywhere in the world. Reliability of forecasts varies by the products you request. Diversity of offerings is excellent, with a wide range of observation and forecast information applicable to most areas of the world. This equipment adds versatility to your communications package, as it handles most of your e-mail needs.

Now on to some other weather solutions: NAVTEX offers basic text forecasts and warnings over medium-frequency radio, covering near-shore waters in portions of the world with good coverage of the Mediterranean in particular. Bandwidth utilization is sufficient for the limited text information provided. Reception is reliable within a couple hundred miles of a station, but many areas have few stations. Many dedicated receivers accumulate messages, so the most recent information is available whenever you desire. Equipment cost is more than a typical VHF radio, but much less than an SSB. Reliability of forecasts varies by geography. There is little diversity of weather products. Equipment receives certain emergency messages, but is mostly just a special-purpose weather tool.

On-demand satellite providers
Since this is not an article on communications per se, I’ll lump all the on-demand satellite providers into a single group, including Globalstar, Iridium, Inmarsat, SkyMate and many others. While each has its pluses and minuses, we can generalize about their weather functionality. Bandwidth utilization is marginal, since you are the only one receiving your data. If 50 vessels in the harbor request the same data, it’s transmitted 50 times. Reception is generally reliable, though there have been service issues with Globalstar. Coverage varies by provider, but most services cover the entire world except near the North and South Poles. (Iridium covers the Poles. Globalstar covers only areas within 1,000 miles of certain land areas.) Cost of equipment varies from about $1,000 to considerably more. Ongoing useage cost varies, but is usually not trivial. You generally pay for the bandwidth you use, either by the minute or by the kilobyte.

SkyMate has some clever ways to reduce bandwidth on their system. Many independent companies (like OCENS, UUPlus and others) have solutions you can purchase to minimize bandwidth use (and save money) on most satellite systems. Reliability of forecasts varies depending on which forecasts you request. You can retrieve just about anything you want from the Internet on most of these services, but they are not generally optimized for Internet access. OCENS WeatherNet offers easy and efficient access to more than 10,000 weather products, with weather available for anywhere in the world. Other independent companies offer products with some combination of ease of use, bandwidth efficiency, diversity of offerings and low cost, but I haven’t found any others that optimize these trade-offs as well for use on satellite communications as OCENS WeatherNet.

Direct broadcast satellite
Direct Broadcast Satellite (DBS) is a relatively new medium for weather delivery. It combines the inherent bandwidth efficiency of “single speaker/many listeners,” much like HF radio broadcasts of weatherfax charts. A single data stream is broadcast from a satellite (instead of a land-based transmitter), and an unlimited number of listeners can receive that stream.

Satellite bandwidth is not free. In order to justify the cost of providing streaming weather content, a broadcaster must be able to sell sufficient subscriptions at a sufficient price to vessels within the geography covered. Hence, we find DBS’s marine weather offerings only in areas with a high density of users interested in a homogenous weather product and willing to purchase subscriptions. In the continental U.S. and adjacent waters, the players are XM (WxWorx),, and Sirius (Weather Channel Marine), In Europe and portions of Africa, it’s WorldSpace,

As the cost of satellite bandwidth continues falling and DBS becomes a more familiar medium for delivery of various content, there will surely be new weather data providers. Indeed, I am aware of one new entrant to the market with an exciting offering possibly covering additional regions of the globe, which I hope to tell you about in a future article.

Reception is reliable due to the tehnique of forward error correction. Coverage is available only in certain zones. Convenience is very high, since most units cache the latest copy of each weather product, so it’s stored on your local machine and available the second you want to see it. Cost is moderate, about $1,000 for the hardware, and no more than $100 a month for the weather subscription. Reliability of forecast information varies, but real-time observational data on some systems is exceptional. Diversity of offerings is moderate, but a new entrant may bring much greater diversity of offerings. Versatility is decent — usually the same hardware and provider offers an inexpensive subscription to a package of 40 to 150 channels of music, news, talk and sports audio entertainment.

Let’s explore some additional technical points. There are many different types of satellites and orbits. Satellite TV broadcasts from a few geostationary satellites, which remain in a very high orbit (about 23,000 miles up). Each satellite has moderately strong transmitters and broadcasts to nearly half of Earth’s surface. These signals are relatively weak when they reach Earth’s surface, requiring a satellite dish, pointed at the satellite, to collect sufficient signal for reception. At sea, this dish must be actively stabilized, which gets large, heavy and expensive for a small vessel.

Some satellites are placed in a much lower orbit. In order to compensate for the stronger pull of gravity, these satellites circle Earth in some fashion. Since these satellites are in a lower orbit, their signal reaches a smaller area of Earth’s surface, and since these satellites are always moving, more of them are required to provide uninterrupted service. Globalstar and Iridium each need as many as 50 satellites to provide uninterrupted service. Sirius’ three satellites are in a lower, elliptical orbit, and provide good coverage to North America and adjacent waters with less power than geostationary satellites.

Yet another type of satellite is used by most DBS providers. They use a geostationary satellite in a very high orbit but, instead of broadcasting a signal to much of Earth’s surface, they focus the beam to a relatively small area, often 2,000 miles across. This provides signal strength sufficient for reception using a simple, non-directional stick or disc-shaped antenna.

Subscription required
To use DBS weather feeds, you need a special receiver and a subscription to the weather offering. Similar to a NAVTEX system, many receivers accumulate and store the latest version of each weather product. But DBS offerings are much more diverse and often include graphical and text observations from buoys and other sensors, satellite imagery, radar, surface analysis, forecast maps and more. Most providers allow you to view content either on specially configured chartplotters, including some from Garmin, RayMarine, Furuno and others, or on your computer.

Since this is not a thorough review of any of these systems, I should warn you to study the weather content carefully and assess whether it fits your needs before you dive in and purchase a system. My impression, supported by feedback from users, is that real-time observational data supplied by Sirius and XM is a real benefit for fast vessels plying coastal waters, where there are lots of buoys and where predictive radar can show you the direction and speed in which squall cells are moving, as well as where lightning has struck recently. However, this data may not be available beyond U.S. coastal waters, and slower boats may not be able to avoid a squall with 30 to 60 minutes warning, but at least you’ll know it’s coming. Forecast offerings are currently less exciting than observational data, but this may change over time.

I do want to spend some time detailing a system you may not be familiar with — RFI Marine from WorldSpace. WorldSpace operates two geostationary satellites with a total of six beams, providing service to all of Africa, Western Europe, Middle East, Asia, including Pacific Islands northwest of Australia, and much of the Indian Ocean. However, at the moment, only a single beam broadcasts weather information to the Mediterranean, most of Europe, northwest Africa and adjacent Atlantic waters.

WorldSpace, in partnership with Meteo France, the French weather service, broadcasts an hour-long audio loop in French with forecasts for portions of the North Sea, North Atlantic from East Caribbean to Azores and to Europe and the Mediterranean. Even better, it broadcasts data you can display on your computer, including text forecasts in English and French for these areas and a synoptic chart. While the RFI Marine channel does not have the long menu of weather products offered by Sirius and XM, it provides useful information to another area of the world not covered by those services.

By Ocean Navigator