By Daniel Piltch, Marine Computer Systems
Weather Software Article
Selecting the Right Weather Equipment
Gone are the days of the old, simple weather fax. The technology was first used in 1926 and has changed very little since 1965 when the modern weather fax program began. Initially, charts were drawn by forecasters and then placed on a cylindrical drum from which they were scanned and sent out over the airwaves as a radiofacsimile. Mariners would have a large black box that received the radiofacsimile from the airwaves via a radio and then printed out the chart embedded in the incoming signal. As a "cordless fax" it was an idea ahead of its time.
For almost forty years, weather charts received by radiofacsimile (or more simply weatherfax or radiofax charts) were a mainstay at the navstation of any vessel venturing offshore for more than a few hours. They continue to be a valuable piece of the weather forecasting puzzle, but recent changes in technology offer more options to the mariner that previously were not available. Instead of black box fax printers using rolls of thermal paper, most vessels are receiving these charts on a computer hooked up to their single sideband radio. And many folks are going even beyond that and finding alternatives to the radio based charts.
The National Weather Service has been aggressive about publishing their chart products on the Internet and making them available for free to anyone who wants to spend the time to find them and download them. You can find many of these charts at http://www.mpc.ncep.noaa.gov/ (waters north of 30°N), http://www.nhc.noaa.gov/ (waters south of 30°N), or http://weather.noaa.gov/fax/marine.shtml. Downloading and printing these chasrts at home before a passage is relatively easy, though accessing them while you're at sea may be more of a challenge.
FTPMail - Weather Charts by Email
Thanks to the efforts of Tim Rulon, Cliff Fridlind and others at the National Weather Service, weather charts are now available on demand via email. The concept is known as FTPMail, which is an extension of the file transfer protocol (FTP) in common use on the Internet. The gist of the service is that you compose an email (at home, on the boat, wherever) which includes instructions detailing which charts you're interested in receiving. The email is sent to a special destination (email@example.com) which then automatically handles all incoming requests without human intervention. Once the message is received, the instructions within are analyzed and a list of charts prepared according to the sender's request. The charts are then attached to a reply email which gets sent back to you. The length of time needed to receive a response can vary greatly, though most charts should be returned within an hour of your request.
The ftpmail service works over just about any email at sea service, though receiving these charts over Inmarsat C would be prohibitively expensive at almost $300 per chart. The size of the charts might also strain the capacities of most single sideband email providers. However, receiving these charts over Iridium, Globalstar, or Inmarsat MiniM is very reasonable as shown in table one.
Inmarsat C is charged by the byte not by minute
Lists of charts and filenames are available at the following websites:
Keep in mind that the ftpmail service is not an official operational delivery method which means that there are no guarantees. While the service has been very reliable, there may be times it's unavailable. Instructions and fine print are available at http://weather.noaa.gov/pub/fax/ftpmail.txt or by sending an email to firstname.lastname@example.org with the word help in the body of the message.
Direct Download (FTP) of Weather Charts
Another way to get the same weather charts in a more direct manner would be to download them directly from the Internet. This bypasses the email system and the exactitude of the ftpmail service, but introduces its own challenges. There are primarily two ways to grab a weather chart off the Internet. The first is to navigate to the appropriate web page, (say http://www.mpc.ncep.noaa.gov/shtml/graphictextA.shtml for popular surface analysis charts) and then click on the chart you want to see. Once the chart is displayed on the screen, you can right click your mouse on the chart's image and save it to your computer for later review.
While this is fine for grabbing a chart or two, it's easy to see how this would be a cumbersome way to retrieve several charts over a slow satellite connection. In addition to the time it would take to display each individual chart (same times and costs as in table one above), you also need to include the time it takes for you to navigate to each web page. Keep in mind you would need to be at the computer during the whole process, being ready to click on each new chart as soon as the old one has been retrieved.
A faster way to retrieve several charts at once is to use the Internet's file transfer protocol or FTP service. While it has similarities to the ftpmail service discussed earlier, this is a different method entirely. With direct FTP downloads, you retrieve charts right when you request them as opposed to waiting for an email response. Most new web browsers include the ability to perform single FTP downloads by typing in an address such as ftp://www.mpc.ncep.noaa.gov/pub/data/mpc/ which should give you a list of files you can select for download.
More advanced users will want to prepare a batch of files to be downloaded all at once without any intervention. There are many FTP programs available that will facilitate this process. My favorites are:
Ocens (www.ocens.com), a Seattle-based weather software company, created a product called WeatherStation 2000 ($179) which packages the FTP batch download software along with a built-in library of available weather charts (so you don't have to know the filenames of each chart), and image processing capabilities to zoom, pan, rotate, and georeference all types of weather chart files including GIF and TIF (see sidebar).
With either of the above methods (ftpmail or direct download), there are significant advantages over traditional weatherfax. The most visually appealing advantage is that every chart you download is crystal clear and perfectly straight with no static on it at all. For those of you that have tried desperately to pull in a weather fax chart from a distant broadcasting station, you can appreciate the benefit of a nice, clear chart. In addition, you're not bound by the transmitting schedules of the weather fax broadcast stations. Rather than have a series of charts trickle in all day long, you can download your charts in a batch at the beginning of a new watch.
Once you get familiar with the products available on the Internet, you'll realize that there is a tremendous amount of information available that never gets transmitted on weather fax frequencies. For example, one of my favorite products is the text based Marine Interpretation Message (MIM), meant to be an internal memo from the Marine Prediction Center in Maryland to the local forecast offices responsible for preparing the VHF NOAA Weather Radio coastal waters forecasts. While most of the MIM is incomprehensible to those without a meteorology degree, there are some significant phrases that may trigger a red flag in your weather prediction routine. For instance, if the message says that all models agree with the previous forecast, then you've can have a reasonably high confidence factor in the charts you see. On the other hand, if you read in the message that there are discrepancies with a particular storm's track you might have a lower confidence factor in the plotted position of the storm on the forecast chart. You can read the MIM at http://www.mpc.ncep.noaa.gov/shtml/graphictextA.shtml.
Comparison of HF Weather Fax and Internet based Weather Chart Downloads
Another new feature available with computer based weather charts is the ability to georeference a chart. By georeferencing a chart, you'll be able to see your vessel's position right on the chart in much the same way you would with an electronic charting program. You'll also be able to simply move your mouse over a certain weather feature and find out how far away it is from your boat.
The process of georeferencing involves selecting a minimum of two points on the weather chart and typing in the lat/long coordinates of these two points. This allows the computer to stretch the lat/long grid to an appropriate size and overlay it onto the weather chart. Two programs that include this feature are Ocens' WeatherStation 2000 and Northport Systems Fugawi (www.fugawi.com).
Many electronic charting programs are beginning to include weather overlays as well. These overlays are distinctly different than the weather fax forecasts prepared by the National Weather Service. The overlays are prepared by slicing up the world into imaginary squares, much like overlaying transparent graph paper on an ocean chart. In each square or box, a wind vector is drawn showing the strength and direction of the wind that should be expected in that part of the ocean for a given time period. Most overlays include the ability to span several days so you can see what the wind is expected to do today, tomorrow, and the next day.
Some overlays include additional information for each box, such as atmospheric pressure, wave height, and so forth. Though as more data is added, file sizes increase proportionally so most recreational marine focused overlays limit themselves to wind and maybe a few other selected data.
Depending on the source of the data, these gridded overlays are often created automatically by a weather forecasting computer program with little human intervention. This science of automatic forecasting is improving constantly, but has a few inherent limitations as pointed out by Environment Canada (http://weatheroffice.ec.gc.ca/model_forecast/about_these_products_e.html):
1) The forecasting programs rely on having a completely accurate picture of the existing conditions before determining exactly how the atmosphere is likely to change. Errors in the initial conditions lead to errors in the forecast. Since the ocean is a notoriously difficult place to gather accurate data, automated forecasting over ocean areas usually needs human interaction to fine tune the resulting forecast.
The gridded overlays are a very useful tool, and are very easy to read especially for mariners new to weather prediction. While their accuracy is excellent, it's important to look at the big picture rather just focus on your individual square of ocean. It's far better to know about the characteristics of a nearby storm system than to focus on a single wind vector and just hope it's accurate.
Look to the future when the National Weather Service is planning to produce their own forecasts in gridded format. These forecasts will have the expertise of the team of forecasters at the Weather Service behind them - rather than simply pass along the computer's output, the forecasters adjust and fine tune the forecast first and then send it out as a gridded file.
Nobeltec's Visual Navigation Suite (www.nobeltec.com), Raymarine's RayTech Navigator (www.raymarine.com), and MaxSea's Yachting (www.maxsea.com) all include the ability to download and display gridded weather overlays. In most cases, these are free downloads - though more advanced features come at a price.
Sidebar: File Formats
Weather charts are prepared as tagged image file format (TIFF or TIF) files. This is the most compact way to ship the files and still have them be legible. The TIF standard is an odd one in that it actually encompasses a few different variations. The Weather Service uses group IV compression in their TIF files. While many newer computers have no problem reading this type of file, you may encounter problems on some older computers. Suggestions for how to decode and view these files can be found at http://weather.noaa.gov/fax/tiff.shtml.
Given the issues people were reporting with TIF files, the Weather Service began preparing their charts in an alternative format: graphics interchange format or GIF. This is a more widely used format, and these files can be read on almost any computer. However, the black & white weather charts tend to be larger when shipped as GIF files rather than TIF files.
In response to the large rise in the number of people accessing charts over the Internet, they added one additional format which is a color version of the GIF files. These color charts are designed specifically for Internet viewing and they're the smallest files available. They tend to be smaller images suitable for display on the screen, but not for printing.
As an example, here are the sizes of today's west Atlantic surface analysis (PYAA06.TIF), which is larger than the average 35 KB file:
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