Changes in marine weather information

Figure 1

For those who rely on NOAA’s Ocean Prediction Center products for their ocean voyaging pursuits — whether through their website, via FTPmail, via HF weatherfax or from other means — you have likely noticed several changes in the past year or so. In this newsletter I will highlight some of the changes that affect more popular products and discuss the new website design, which may affect how products are found and obtained.

Starting with the website, although the old address will still work, the address has been updated to It would be a good idea to update any bookmarks that you have set to reflect this change, since at some point in the future the old address will no longer work. The front page looks quite different than it did a year ago with six basic areas of information highlighted in links on the right side of the page. For each of these links, a representative image is shown, and for some browsers it will rotate through the six topics until one is selected. In each case, clicking on the large image will take you to a new page where a larger selection of products can be accessed. There are also menus across the top from which information, data and products can be obtained.

Let’s look first at the “Weather” link on the right. When this is clicked, a surface analysis chart of the Pacific Ocean is seen. Clicking this image will send the user to a page with a larger selection of Pacific products that looks quite a bit like the previous home page of the website. There are links across the top of this page to shift to Atlantic or Alaska/Arctic products. In addition, on the front page there are links below the Pacific surface chart to go directly to the Atlantic or Alaska/Arctic products.

For each basin, analysis charts as well as forecast charts can be found for 24, 48, and 96 hours after the analysis time. Recall that these charts will not be available right at the analysis times (0000 UTC and 1200 UTC) but rather a few hours later to allow time for the meteorologists to gather and analyze the data and produce the charts. Also recall that 96-hour products are only produced on the 1200 UTC forecast cycle. The charts that can be obtained from this page all include color for the weather symbols, though the background is white. Loops of each chart (three, seven or 14 days long) can be obtained from this page as well.

Figure 1: Atlantic 500-millibar analysis chart from 1200 UTC 16 February 2016. This is the old style chart produced by a meteorologist, and includes trough axes as shown by the dashed lines.

There are some changes in the 500-millibar charts presented on this page that were implemented on November. These charts are no longer produced by meteorologists but rather are derived solely from numerical model output. The trough axes are no longer included, which leads to a somewhat different look to the charts (see Figure 1 and Figure 2). The OPC has explained that in recent years meteorologists were making very few changes to the numerical output when producing the charts, and that time spent to include the trough axes was needed for other tasks. While the flow pattern at 500 millibars can still be determined from the charts, the lack of trough axes does remove information that many mariners may have found useful. Also, because the surface charts are still produced by meteorologists considering input from several different computer models along with the expertise of the forecaster, there will be times when the forecast charts do not match up with the 500-millibar charts as well.

The black and white charts are a bit more difficult to find on the new website, and since many will want to be able to access these versions of the charts because they are easier to print and because the files are smaller (better for slower offshore connections), it is useful to go through the process to obtain them. One of the best ways to obtain charts offshore is to use the FTPmail system. The best instructions for this can be found be hovering over the “Information” menu at the top of each page of the website, then clicking on the “Radiofax Schedules” link under “Receiving Products.” (Note: This is NOT the FTPmail link!) Since you will also need the radiofax schedule to determine when products will be available and to obtain the FTPmail ID for the charts of interest, click the link for the ocean basin of interest to obtain this. Right above the schedule in red text, there is a note about the FTPmail program that contains a link to the directions about how to use the program. It is strongly advisable to print a copy of the instructions and the schedule to make for easy access to this information when offshore. The web version of the radiofax schedule has links directly to the charts of interest, including the two different black and white versions (GIF and TIF). Charts received through FTPmail are generally TIF charts as they are the smallest files.

Another way to obtain black and white charts is by using the briefing pages. These are accessed by hovering over the “Analysis & Forecast” menu at the top of each page, then clicking on “Briefing Pages” under the “Weather” subheading. This will provide a copy of each type of chart. It is important when examining the charts on the briefing pages to make sure the charts are all from the same forecast cycle. These pages will always provide the most recent charts available, but this means that if the page is accessed before all of the charts from the current cycle have been produced, then some charts from the previous cycle will be presented. Check the “Issued” and “Valid” times carefully, and if some charts are not updates, try again at a later time. The briefing pages and the radiofax schedules are now the only place that 500-millibar analysis charts can be found (500-millibar forecast charts are available on the web page for each ocean basin).

Figure 2: Atlantic 500-millibar analysis chart from 1200 UTC 28 December 2017. This is the new style chart derived from GFS model output. Trough axes are not indicated.

The Ocean Prediction Center is moving in the direction of more digital products, and their contribution to the National Digital Forecast Database is now operational and available through their website. Click on the “Digital Forecasts” link on the right side of the front page, then click on the image, then click on “NDFD Grid Viewer” and you will be brought to a graphic display page. The parameters available for ocean forecasts are wind speed and direction, wind gusts and significant wave height. These can be displayed by using the drop-down menu at the upper left of the image. The forecast time can be adjusted at the top right of the image. All of the data displayed through this interface is forecaster generated — in other words, it is not pure numerical model output like many other graphic display products from private vendors. By moving the cursor around the map, data for any given point is displayed at the upper right. This interface offers a new way to access forecast information, but it requires full Internet access and may not be practical at this time for offshore use because of slow connection speeds.

There are many other changes to the OPC website and other available products. During the Northern Hemisphere winter, ocean voyagers should take the time to become familiar with the new website and the product changes in order to be ready for the 2018 sailing season.

By Ocean Navigator