We had one tidal revolution in 2021 when NOAA announced that they were discontinuing the decades-long use of Table 2 lists of secondary station corrections, and that there will no longer be any sanctioned annual Tide and Current Tables. Plus there will no longer be any international tidal data published by NOAA. Going forward, the way we get official tide and current predictions is go to tidesandcurrents.noaa.gov and create a monthly or annual table for specific stations as PDFs and then print them. It takes four pages per year, per station. This is a superior system, as we rarely needed the global coverage in the historic annual tables, plus the use of Tables 2 (one for tides and one for currents) was tedious, and, indeed, we learn now, not accurate in many cases. We still see in 2025 the discontinued 2020 Tables 2 in some third-party tide or current books, but it is important to know that much of that content is wrong.
The USCG have also now recognized that historic tidal predictions have not been valid since 2021 and the new round of license exams have removed all Table 2 references in lieu of the modern approach of direct data from tidesandcurrents.noaa.gov. This is also now updated in all electronic navigational charts (ENC). All previous references to “NOAA Tide and Current Tables” have been removed.
But with that revolution still unknown to many mariners, we have a new one! NOAA’s new Operational Forecast System (OFS) now produces digital tide and current forecasts that are superior to the traditional NOAA predictions, which are based on harmonic constants for each station. We now have tidal current forecasts uniformly over the full waterways, out two or three days, in fifteen regions and two channels around the country.
The beauty of the OFS model forecasts is they take into account the local values of wind and pressure, as well as unseasonal river runoff. The models are updated four times a day to account for changes in these local environmental factors that affect tide height and current flow. The model data has a latency of about 2 hours, meaning a 3-day set of hourly forecasts run at 12z will be available to mariners at about 14z.
The other huge improvement are the OFS current directions. Traditional harmonic currents are presented as pure reversing currents with just two directions, being the average flood and average ebb directions. But most open water currents are rotating currents to some extent, which do not have just two directions. An example is in Figure 2.
Where to get OFS tide and current forecasts.
For the time being, NOAA presents the OFS forecasts as graphic animations such as shown in Figure 3. These animations are not a very precise way to access this very precise data, but they are working on other presentations. In the meantime, third party navigation apps have solved this problem for us, which we come back to shortly.
NOAA is also working on a new OceansMap web app that promises to be a sophisticated digital display that replaces the Figure 3 animations. A sample from the beta version is shown in Figure 4.
In the meantime, we also have presentations from other agencies. A particularly nice one is from the Northwest Association of Networked Ocean Observing Systems (NANOOS) for the Salish Sea region shown in Figure 5.
These graphic presentations show us the general flow of the tidal currents, revealing patterns we would never know from the isolated harmonic station predictions alone, but for actual navigation underway we need the digital data in GRIB format. This way we can load it into navigation programs and compute optimum routing for all classes of vessels, but this is specifically crucial to sailors and low-powered craft. The problem is the official data are only published in NetCDF format, which most nav apps cannot read.
But mariners can be grateful to two marine navigation apps who have taken it on their own to convert this crucial data to GRIB format. They are Expedition and LuckGrib. The former is a popular racing and performance PC app, and the latter is a state of the art marine weather data source and display for Mac and iOS. Both can incorporate OFS currents into optimum inland routing computations. Both apps also allow users to export the OFS grib files they created. LuckGrib has a two-week, full-function demo period, so users can experiment with this OFS data and other features it offers.
Figure 6 shows the Salish Sea OFS grib file exported from LuckGrib and then loaded it into qtVlm, another nav app which is chosen here because it can display the OFS forecasts as well as the NOAA harmonic station predictions so we can compare the two current sources. qtVlm is a free app for Mac or PC.
the speeds are usually pretty close, which gives us confidence that the model data are right at other locations. The differences in directions between model and harmonic currents can be larger in between the peak and slack samples shown
here. We are reminded in the slack data (bottom picture), that slack water is rarely still water — the model data makes this even more apparent.
Usually tidal currents affect our navigation more than the tide heights themselves, but there can be exceptions, and the OFS model includes tide heights that can help with this. One example would be predicting current flow along a narrow channel that has no harmonic predictions nor OFS current forecasts for the channel. Such cases are usually controlled by the tide height at each end, with current flowing from the higher-tide side toward the lower-tide side. An example is shown in Figure 7.
— David Burch, PhD, FRIN, is the director of Starpath School of Navigation in Seattle and the author of textbooks and online courses in marine navigation and weather. He is a recipient of the Superior Achievement Award from the Institute of Navigation for outstanding performance as a practicing navigator.
