The definition of a weather briefing from the Glossary of Meteorology, published by the American Meteorological Society is: “Oral commentary on existing and expected meteorological conditions.” A further definition is given in the same publication for a Pilot Weather Briefing is: “Oral commentary on the observed and forecast weather conditions along a route, given by a forecaster to the pilot, navigator, or other air crew member prior to takeoff.” These definitions were created many years ago when the resources available were more limited in terms of graphics and in terms of longer range forecasts. In fact, most pilot briefings were conducted by telephone with no reference to weather charts. Charts may have been available at larger airports, but the lag time in receiving the charts made them less useful for an imminent departure. For mariners, because forecasts were generally not available for more than a few days, briefings were of more limited use since they could not cover the large majority of longer ocean passages.
In more recent years the availability of more reliable longer range forecast information over the oceans and the timely availability of graphics has led to more extensive weather briefings being possible for mariners. A more accurate definition for a marine weather briefing today is shown in the sidebar. It’s kind of a long, somewhat verbose definition, but with more information available, briefings have become more comprehensive. Let’s dig into the definition a bit and look at some of the differences from the earlier definitions.
Participating in weather briefings
First, note the change in the first sentence of the word “or” to “and”. While the captain or skipper has the ultimate responsibility aboard the vessel, there are others on board who have significant responsibilities as well, and they should participate in any weather briefings. There is a lot of information disseminated in a good weather briefing, and the more ears that hear it, the better in terms of the overall vessel management. Also, should the skipper become incapacitated for any reason, it is critical for others on board to be able to expand their roles to fill the gap. If they have not received the full weather briefing, then they will be at a disadvantage that negatively impacts the management of the vessel.
The definition also makes note of a discussion, and the opportunity of the crew to ask questions. This speaks to the idea that a weather briefing should not be a one-way conduit of information from the presenter, but should be viewed as an opportunity for the onboard crew to fully understand the weather situation that they will be dealing with while underway. Crew members who attend a weather briefing should have this as a goal, and should be encouraged to ask questions of the presenter. Even if crew members believe they fully understand the presentation, verbalizing this during the briefing may help the presenter to clear up any misunderstandings, and may also spark questions from other crew members. Such discussion can also help the presenter to more fully understand the needs and concerns of the crew.
The contents of a good marine weather briefing will include much more than just a text forecast for the coastal or offshore waters or the high seas. As noted in the definition, graphics like weather charts, satellite images and, when close to shore, radar data should be included. A generation ago, the text forecasts were often all that was available, particularly for a vessel at sea. These text forecasts are still issued, and still contain relevant information, but with weather charts and other graphics now available in near real time, and better connectivity allowing computer use offshore, a much better understanding of the weather situation can be obtained which allows for better decision making both prior to departure and while underway.
Most ocean yacht races now feature a weather briefing by a meteorologist prior to the start of the race. Many cruising rallies also offer this service. These briefings generally occur in an auditorium setting where the meteorologist can display charts on a large screen. The meteorologist is aware of the start time of the event and the race course area (or the proposed itinerary for the rally) and in addition to presenting information about the expected weather pattern through the duration of the event, can speak to specific conditions that are likely to be encountered during the event. In some cases, the meteorologist may recommend a change in the start time and/or the planned route of the event if it appears that the original schedule would pose an unacceptable risk for the participants.
Other options to consider
For many other ocean voyages, though, particularly those that involve a single vessel moving from one port to another, having a meteorologist provide an on site briefing is not practical. How can an effective briefing be put together for these situations? There are a few options to consider, all of which require that the captain and crew of the vessel have some understanding of weather systems as well as the weather products that are publicly available. This knowledge can be gained by attending seminars or webinars which may be offered and spending a fair amount of time becoming familiar with the weather forecasts, charts, and other products that are easily obtainable. With this knowledge, a skipper or navigator can put together their own briefing for their vessel and crew.
NOAA’s Ocean Prediction Center provides briefing pages on their website, which allows mariners to examine and download the full suite of text and graphical products all in one place. The text products include the offshore waters forecasts, and also the high seas forecasts. The graphical products include all the forecast charts through the 96-hour forecast cycle. This includes surface charts, 500 millibar charts, wind and wave charts, and wave period and direction charts. It is important when accessing these products to pay close attention to the issuance times to make sure that the most recent products are shown. Typically the longer range graphic products become available a little later than the shorter range products. The briefing pages show the most recent version of each product, and this means that at times older products (from previous forecast cycles) of longer range products may be shown at the same time as more recent versions of shorter range products. For example, at certain times, a 72-hour forecast chart will have the same valid time as the 48-hour forecast chart because the 72-hour forecast from the prior day is still being displayed. In this case, it is best to check again a bit later to obtain the most recent products. In general, graphic products from the forecast cycle initiated at 1200 UTC are all available by 1900 UTC or so. For the 0000 UTC forecast cycle, graphic products are only produced through the 48-hour forecast time period, and are generally available by about 0600 UTC.
Keep in mind that the goal of a weather briefing is to come away with a fairly complete understanding of the weather situation as it will impact your vessel and its passage. This requires examining all of the charts that are available, and using these charts along with an understanding of weather systems to get the full picture. As an example, figures 1 through 4 show all of the 48-hour forecast charts from the the Ocean Prediction Center’s Atlantic briefing page. The 500-millibar forecast chart indicates a closed low over the southeastern U.S., and also a trough axis in the central Atlantic along about 43 degrees W, extending south from and upper level low east-northeast of Newfoundland. These features coordinate with the surface forecast chart that indicates low pressure in the Carolina coastal waters producing gale-force winds, and a large and strong low over the north central Atlantic producing storm-force winds with a pair of cold fronts extending south to the east of 40 degrees W, then southwest into subtropical latitudes.
The wind wave forecast chart indicated the largest significant wave heights in the north central Atlantic associated with the large and strong low in that region, and another area of high seas off the southeastern U.S. coast being produced by the southern winds to the east of the coastal low. The wave period and direction forecast chart shows the expected direction of the dominant waves, and their expected periods.
Together these four charts provide a good picture of where the weather features are expected to be at the forecast time, and of the conditions that they will produce. It is possible by examining the flow pattern on the 500-millibar chart as well as arrows for warning category lows on the surface chart to make some estimations as to how systems will move and change in strength during the period following the valid time of the charts. Looking at the low along the southeastern U.S. coast, it is forecast to move generally northeast and become stronger. The 72-hour surface forecast chart (Figure 6) bears this out, showing the low center east of Delaware Bay. With the low in this position, its circulation will be producing gale-force easterly winds to its north, and this will have an impact on the sea state in the mid-Atlantic coastal waters as indicated on the 72-hour wind wave chart (Figure 6).
These charts are just a subset of what is available, and of the charts available on the briefing page should be sequenced and utilized within the briefing which will allow the weather situation through four days to be fully visualized (five days or a bit more when using the 24-hour forecast arrows of warning category lows in the 96-hour surface forecast and by analyzing the 500-millibar flow pattern). In addition, one can examine the offshore and high seas text forecasts to obtain more details on the warning areas shown on the surface charts.
When a skipper or crew member has the responsibility of providing a briefing to the rest of the crew, it is important that this crew member spend a fair amount of time examining the briefing materials ahead of time in order to be conversant enough to be able to present a full weather picture and to answer questions from the crew. In fact, the preparation for the briefing generally takes longer than the presentation of the briefing. As noted above, anyone providing a weather briefing needs some basic knowledge of weather systems and of the forecast products, and this should play a role in who onboard is tasked with this responsibility.
New briefing product available
There is a new briefing product available from the National Hurricane Center’s Tropical Analysis and Forecast Branch (TAFB) which can be useful if operating in the waters south of 30 degrees N in the Atlantic or in the Caribbean Sea or the Gulf of Mexico. These are video briefings with NHC forecasters displaying the charts and providing a narration. At present they are made available twice per week on the NHC YouTube account.
To sum up, a weather briefing prior to an ocean voyage is a critical part of departure preparations, and regular briefings while underway should be also be arranged. The most ideal situation is to have a meteorologist provide such a briefing, but practically, this is only likely to occur in connection with ocean races or cruising rallies. This leaves individual skippers or navigators with the responsibility of putting together briefings. This requires knowledge of weather systems and the forecast products that are available, so getting some education and training in advance is necessary. The briefing products produced by NOAA’s Ocean Prediction Center and National Hurricane Center can be very helpful. There are other resources available from private vendors which can be included as part of a briefing, such as displays of forecast model winds and seas, but these products should not be used in isolation. In particular, in the absence of a meteorologist, it is important to include products that are produced by meteorologists as part of the briefing. These can include the NOAA products noted above, and can also include a forecast and recommendations provided by a meteorologist serving as a weather router. In fact, such meteorologists are generally available for questions after providing their forecasts and in some cases may provide a full briefing remotely. ν
Contributing editor Ken McKinley is a professional weather router and the owner of Locus Weather in Camden, Maine.