Assessing the Marine Forecast

Matt Everett   Apr 12, 2023

Ever wonder how to decide what site to head to? How do instructors know where to conduct training before you are at the beach? The secret is marine forecasts! Marine forecasts allow divers to see wind direction, strength, and estimated wave height for a given location without having to physically be at a dive site. Now, you should always reassess conditions at a dive site before getting in the water because forecasts are not 100% accurate but generally marine forecasts allow you to eliminate certain sites that you know will not be safe or diveable on a given day because of the wind. The most important factor with wind is the direction because this determines what sites receive the most waves. Stronger (aka faster) winds carry more energy and thus cause larger waves, but the wind direction is the more important factor. At the base level, wind moves water; water moving causes waves and currents which influences how divers approach a dive and how they act while in the water.

Wind direction is always described via compass directions (North, South, Southeast, Northwest, ect) and represents the direction the wind is coming from. So, if we have a Northwest wind, that means the wind is coming from the Northwest and heading in the opposite direction (180 degrees opposite, toward the Southeast). Now what does that mean for divers? Because the wind is coming from the Northwest, any site that faces Northwest will have the strongest wave action because the wind is blowing directly at the site and the waves have the most amount of time on the open ocean to build up speed and energy. Sites facing the opposite direction (Southeast in this example) should be the calmest option. Basically, you want to head in the opposite direction from the wind. That is why Cape Ann is so fantastic for diving! Because it’s an island there is always a leeward side (side away from the wind), and you can usually find a cove or protected area to slip into and get a dive in. The directions do not have to match perfectly, you do not have to only dive at sites directly opposite the wind direction. For example, let’s say you want to head to Pebble Beach in Rockport. This site faces directly South, and the wind today is from the Northeast. This site will be a great option for diving because the wind will be blowing from the shore towards the water. The site does not need to be perfectly lined up in the direction opposite the wind (in this example, directly opposite would be Southwest). From our experience, even West or East winds are adequate for diving at Pebble beach if the wind speed isn’t too strong and you are aware there will be a current flowing in the direction of the wind. By compensating for the expected current during the dive, you can get in and dive without getting disoriented on your dive, all thanks to the forecast!  

 

Now that you know the importance of marine forecasts and how to interpret wind conditions, let’s take a look at some ways to find wind conditions. There are many resources and websites available for free that give you a detailed forecast but try not to use conventional weather reports because those are designed for people on land; we want ocean conditions. The most popular resources are from NOAA (National Oceanic and Atmospheric Administration), windy.com, and windfinder.com. Here at Undersea Divers, we always use the NOAA Marine Forecast because we find it to be the most reliable and often other sites or organizations use data collected by NOAA for their forecasts, so we like to go straight to the source! Their marine forecast gives a full spectrum of details such as wind direction, wind strength, and wave height for the conditions currently, overnight, and several days in the future. It is important to note that their estimated wave heights are just that: estimations. Their listing of the expected wave heights uses a method called significant wave height, which is the average of the highest third of the waves. Individual wave heights may be more than twice the significant wave height! So always make sure to reassess conditions at the beach before you get in the water: just because the forecast implies it will be nice at a site does not necessarily mean it will be! It is always up to you to make the decision to go in the water and always dive within your training and comfort levels. The NOAA Marine Forecast is also beneficial because they give overnight predictions which allow you to see how conditions will change over time. Maybe today the wind is from the South but overnight it shifts to the East and tomorrow the wind will be from the North. This allows you to plan out multiple days of diving or can provide insight into what day will have the best conditions for an intended dive site. Say you want to dive at a site where the tide is important such as Folly Cove on the Gloucester/Rockport town line. This site has a tricky entrance and exit so it is important to dive there at high tide. You can look at a tide chart and find days when the high tide will be in the morning (so you have an easier time while parking) and then as you approach that date you can begin to look at the marine forecast to make sure the wind will be favorable for diving there. 

Another great benefit of the NOAA Marine Forecast is how often it is updated. This forecast is updated several times throughout the course of the day and when you load into the forecast, they give you a synopsis of upcoming marine weather and states the time the forecast was last updated. This helps you get a better understanding of marine weather conditions as they develop: next time there is a big storm rolling in, check out the marine forecast in the morning and again in the evening and see how the predictions have changed over the day. NOAA also issues hazardous weather warnings during storms or rough conditions which are usually a good indicator that it might not be the best time to go in the water! 

Sites like windy.com and windfinder.com are great resources but focus more on wind conditions because they are primarily used for activities such as sailing. While their maps are fun to look at (check out their websites and you will know what we mean!), we find the vast amount of information provided by the NOAA Marine Forecast pushes them to the front of the line as our go to dive conditions resource. 

 

 

                      

 

 

 

 

Check out the Massachusetts NOAA Marine Forecast on their site here. Just click on the corresponding region you will be diving in, and it will give you the detailed forecast for that area (Cape Ann is ANZ251: Massachusetts Bay and Ipswich Bay section, AKA the plum colored one at the top!) 
https://www.weather.gov/marine/boxmz

Here is a list of popular dive sites and what directions they face.

Old Garden Beach: faces Northeast
Back Beach: faces East 
Folly Cove: faces Northeast 
Pebble Beach: faces South
Loblolly Cove: faces North to Northeast 
Cressy Beach at Stage Fort Park: faces South to Southeast 
Niles Beach: faces West but is very protected inside the harbor 
Plum Cove: faces Northwest