Forecasts and Predictions
Meteorologists generate marine weather forecasts by utilizing meteorological and oceanographic observations, forecast guidance from different numerical weather and oceanographic prediction models, and their knowledge and expertise. Marine weather forecasts focus on providing predictions out to five days of conditions such as wind, waves, visibility, significant weather (e.g. fog, showers, thunderstorms), and ice accretion in the winter months.
Forecasters examine the analyses of weather observations (e.g., winds, pressure, temperature, humidity) taken by thousands of automated weather stations on land and along the coast, fixed and drifting buoys, ships, upper-air soundings, commercial aircraft, weather satellites, and weather radars. They also rely on ocean observations (e.g., wave heights, water temperatures) from coastal stations, fixed and drifting buoys, and ships.
Forecasters interpret weather forecast guidance from several numerical weather prediction models, which are computer simulations of the atmosphere. These models use complicated mathematical equations that govern how the state of the atmosphere changes with time, requiring supercomputers to solve them to meet forecast deadlines. The forecast models are usually run four times per day and generate guidance for several days into the future. In addition, marine forecasters will examine forecast guidance from numerical wave forecast models and oceanographic circulation forecast models to help them predict wind waves and swell conditions. These ocean models also typically run four times per day.
Mariners rely on NOAA’s National Weather Service (NWS) marine weather forecasts, along with tidal predictions and forecast guidance from NOAA’s weather, wave, and ocean circulation forecast models, for safe and efficient marine navigation. Many of NOAA’s products and services that are useful for marine navigation can be found in the drop-down menu below.
NOAA is leading the development of standards that will enable model forecast guidance and marine weather forecasts to be included in its suite of precision marine navigation services. The goal is to make more of NOAA’s near-real-time and forecast information more accessible to mariners onboard ships. For example, forecast guidance for surface water currents (S-111 format) is already available on the prototype Precision Marine Navigation Dissemination System and NowCOAST Viewer for most U.S. coastal waters and the Great Lakes. Forecast guidance for water levels (S-104) and marine weather and wave forecasts (S-41X) is currently under development, and more information on these data formats can be found on the S-100 page.
Predictions involve the use of equations to represent environmental forcing to estimate environmental conditions at a given location and time. NOAA produces predictions for tides and tidal currents, both of which are useful for navigating U.S. coastal waters.
Tide predictions are a calculation of what the water level will be based on tidal harmonic constituents - driven by lunar cycles. The predictions are offered in various time intervals and can be referenced to a variety of tidal datums. They can be generated "on-the-fly" for all stations with harmonic constituents. Tide predictions are useful in navigation for vessel transit planning to determine timing of high and low water.
Example of 48-hour view of NOAA tide predictions, showing the predicted time and height of high and low tides. Water level height in this image is relative to the Mean Lower Low Water (MLLW) tidal datum. The green depicts the current time when the predictions were viewed.
NOAA (NOS) Tidal Current Predictions
NOAA’s tidal current predictions display the predicted time and speed of maximum flood currents, ebb currents, and the timing of slack water for all official NOAA current stations. A flood current refers to the incoming tide along the coast and into bays and estuaries, while an ebb current refers to the outgoing tide. Maximum flood and ebb currents generally occur right before or near the time of high and low tides. Slack water refers to the period of time when the current is weakest, and there is a lack of movement either toward or away from the shoreline. Determining the timing of peak flood and ebb currents, as well as slack water, can be useful for vessel transit planning and can lead to more efficient vessel movements.
Example of 48-hour tidal current predictions for the Bayonne Bridge station. The table on the right shows the predicted time and speed of the max flood and ebb currents, as well as the predicted times of slack water.
Forecast guidance refers to computer-generated output that utilizes environmental forcing equations and observations to assist in the preparation of a forecast. Numerical weather and oceanographic forecast models produce forecast guidance for various oceanographic and atmospheric conditions at both the global and regional scales.
NOAA’s National Centers for Environmental Prediction (NCEP) develops and maintains several weather, ocean, and climate numerical guidance systems. A full list of the operational models run by NCEP can be found on their Numerical Forecast/Analysis Systems webpage. Descriptions of and links to the forecast modeling systems that are useful for navigation can be found below.
Animated precipitation map produced from a run of the Global Forecast System (GFS).
Global Forecast Modeling Systems
The model runs as a coupled component to the NCEP Global Forecast System (GFS) and Global Ensemble Forecast System (GEFS). The NWS/NCEP operational global wave model (WAVEWATCH III) produces forecast guidance for wave height, direction, and period, as well as wind speed and direction, throughout the world’s oceans was replaced by this model. Users can choose between local, regional, and full-basin forecast zones to view the forecast guidance for several wave and wind conditions (e.g., significant wave height; primary swell wave height; peak wave period). The model is run four times each day, and each run produces hourly forecasts out to 120 hours and 3-hour forecasts out to 180 hours.
Global Real-Time Ocean Forecast System (GRTOFS)
The National Weather Service (NWS) Global Real-Time Ocean Forecast System (GRTOFS) provides forecast guidance for water levels, water temperature, salinity, and currents out to 144 hours (6 days) for most of the world’s oceans. The "Nowcast/Forecast Viewer" allows users to visualize the forecast guidance of each condition, and the model data can be downloaded as individual NetCDF files, OpenDAP urls, and regional GRIB2 files. The model has one forecast cycle per day at 0000 UTC, which uses 3-hourly meteorological forecast guidance from the NWS/NCEP Global Forecast System (GFS); each forecast cycle is preceded with a 48-hr long nowcast/data assimilation cycle. The system uses the Hybrid Coordinates Ocean Model (HYCOM), an eddy resolving, hybrid coordinate numerical ocean prediction model; it has a horizontal resolution of 1/12 degree and 32 hybrid vertical layers.
NOAA (NOS) Global Extratropical Surge and Tide Operational Forecast System (Global ESTOFS)
NOAA’s Global Extratropical Surge and Tide Operational Forecast System (Global ESTOFS) provides users with nowcasts (analyses of near present conditions) and forecast guidance of water level conditions for the entire globe. Global ESTOFS serves the marine navigation, weather forecasting, and disaster mitigation user communities. The modeling system is run four times per day, and water level forecast guidance is provided out to 180 hours (nowcast for previous 6 hours followed by 7.5 day forecast). Forecast output includes water levels caused by the combined effects of storm surge and tides, by astronomical tides alone, and by sub-tidal water levels (isolated storm surge). The hydrodynamic model employed by Global ESTOFS is the ADvanced CIRCulation (ADCIRC) finite element model. Global ESTOFS has a coastal horizontal resolution of at least 1.5 km and up to 80 m globally. Global ESTOFS is a collaborative effort led by the NOAA/National Ocean Service (NOS)/Office of Coast Survey along with the NOAA/National Weather Service (NWS)/National Centers for Environmental Prediction (NCEP) Central Operations (NCO), the University of Notre Dame, Argonne National Laboratory, the University of North Carolina, and The Water Institute of the Gulf.
Coastal Forecast Modeling Systems
NOAA (NOS) Operational Oceanographic Forecast Modeling Systems (OFS)
NOAA provides forecast guidance for water levels, water temperature, salinity, and currents to help mariners safely navigate their local waters. The guidance is generated by a national network of numerical oceanographic forecast modeling systems for the next 48 or 120 hours depending on the water body. These forecast modeling systems are usually run four times per day (e.g. 0, 6, 12, and 18 UTC). The systems are implemented in critical ports, harbors, estuaries, Great Lakes and coastal waters of the United States, and form a national backbone of real-time data, tidal predictions, data management and operational modeling.
Depiction of surface currents for part of the New York/New Jersey Harbor, based on the OFS available there (NYOFS).
Nearshore Wave Prediction System
The Nearshore Wave Prediction System (NWPS) provides on-demand, high-resolution nearshore wave model guidance to U.S. coastal WFOs, triggered in real time by forecast wind grids prepared and submitted by the individual offices. Through an interactive map, users can find forecasts for significant wave height, peak period, wave direction, and wind speed out to 6 days for several stations along the U.S. coastline.
Advanced Hydrologic Prediction Service (AHPS)
Advanced Hydrologic Prediction Service (AHPS) is a new and essential component of the NWS’s Climate, Water, and Weather Services. AHPS is a web-based suite of accurate and information-rich forecast products. They display the magnitude and uncertainty of occurrence for floods or droughts, from hours to days and months, in advance. Although AHPS focuses mainly on forecasts of water levels along rivers, it does provide time series plots of observed and predicted water levels at many coastal locations.
Marine weather forecasts involve human effort to predict environmental conditions for a given location and time through the use of forecast guidance from numerical models and current observations. The National Weather Service (NWS) Marine Weather Services Program offers a broad range of marine forecast and warning products in both graphical and text formats. A full list of the NWS marine text forecasts and products can be found here.
NWS also offers Marine Point Forecasts, which are hourly text forecasts for a single point in a marine zone. These forecasts are very specific and typically limited to an area of around 2.5 km by 2.5 km, and mariners should also be aware of the weather conditions in the surrounding area. Point forecasts are generated by the National Digital Forecast Database (NDFD), a suite of gridded forecasts of several weather elements. In the NDFD, forecasts are available for wind speed, wind gusts, wind direction, and wave height.
Image of the NDFD display, showing the marine coverage for wave height in purple.
NWS Marine Forecast Areas
NWS provides marine weather forecasts for coastal waters (typically from shore out to 60 nm), offshore areas beyond the coastal zones out just beyond the U.S. Exclusive Economic Zone (about 250 nautical miles), and the high seas (beyond the offshore zones). The coastal forecasts are the responsibility of local weather forecast offices, while the Ocean Prediction Center (OPC) and Tropical Analysis & Forecast Branch provide forecasts for offshore and high seas areas. The Alaska Forecast Offices, Honolulu Forecast Office, and National Hurricane Center (NHC) also contribute to the offshore and high seas forecasts for their respective areas. Interactive maps of all the NWS Marine Forecast Areas can be found here.
NWS Marine Forecast Areas for the North Atlantic (left) and North Pacific (right).
The Ocean Prediction Center (OPC) develops and issues marine warnings and forecasts, continually monitors and analyzes maritime data, and provides guidance on marine atmospheric variables for offshore zones and the high seas. Their forecasts and services ensure the safety of commercial and recreational fishing, boating, and shipping activities in these waters. OPC provides forecasts and warnings in both text and graphical formats out to five days in advance, many of which are issued daily. Their forecasts are also transmitted directly to vessels at sea and the public along coastal areas via High Frequency (HF) short-wave radio at scheduled times throughout the day.
OPC also provides forecast points in coordination with the National Hurricane Center (NHC) for Tropical Cyclones in the Atlantic Ocean E of 60W and N of 20N. In emergency situations, OPC acts as a backup to the National Hurricane Center (NHC) and the Honolulu National Weather Service Office and takes over marine functions. Those offices also act as backups to OPC's marine functions. In addition to the products found on their website, many OPC products are also available over radiofax (also known as weatherfax) on upper side-band (USB) radio. For more information about NWS products available via radiofax. Most of these radiofax charts can be requested and received via email using file transfer protocol (ftp) commands. For more information on how to receive NWS charts and text products via email, see: https://www.weather.gov/marine/faq#3
Tropical Analysis & Forecast Branch at NHC
The Tropical Analysis and Forecast Branch (TAFB) provides forecast products for the tropics and subtropics, such as forecasts for the high seas and offshore waters, surface weather analyses, and experimental gridded marine forecasts. In addition to the products found on their website, many TAFB products are also available over radiofax (also known as weatherfax) on upper side-band (USB) radio. For more information about NWS products available via radiofax, see https://www.weather.gov/marine/radiofax_charts
Most of these radiofax charts can be requested and received via email using file transfer protocol (ftp) commands. For more information on how to receive NWS charts and text products via email, see https://www.weather.gov/marine/faq#3
The TAFB consists of highly trained meteorologists who specialize in marine meteorology, tropical meteorology, satellite imagery interpretation, and tropical weather analysis. The TAFB is staffed 24 hours a day, 365 days per year with at least three meteorologists working at all times. It is supplemented by additional staff during hurricane season. As an integral part of the National Hurricane Center, the TAFB performs forecasting, outreach, and support functions.
Weather Forecast Office - Honolulu
WFO Honolulu is also considered a national center since they produce offshore and high seas forecasts, warnings and services. Here is their marine page - https://www.weather.gov/hfo/marine.