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This nowCOAST™ time-offsets map service provides maps depicting the NWS
significant wave height forecasts from the National Digital Forecast Database
(NDFD) at 6-hr increments out to 3 days. (NDFD has forecasts of waves out to 6
days which are available via the nowCOAST™ time-enabled map service for
NDFD elements.) The wave heights are displayed in units of feet. The wave
heights are indicated by different colors at 2 feet increments up to 20 feet
and then at 5 feet increments up to 40 feet. The forecasts are updated in the
nowCOAST™ map service four times per day. For more detailed information about layer update frequency and timing, please reference the nowCOAST™ Dataset Update Schedule.
The significant wave height is defined as the average height (trough to crest)
of the highest one third of waves.
The NDFD is a seamless composite or mosaic of gridded forecasts from individual
NWS Weather Forecast Offices (WFOs) from around the U.S. as well as the NCEP
Ocean Prediction Center and National Hurricane Center/TAFB. NDFD has a spatial
resolution of 2.5 km (1.6 miles). The time resolution of forecast projections
varies by variable (element) based on user needs, forecast skill, and
forecaster workload. Each WFO prepares gridded NDFD forecasts for their
specific geographic area of responsibility. When these locally generated
forecasts are merged into a national mosaic, occasionally areas of
discontinuity will be evident. Staff at NWS forecast offices attempt to resolve
discontinuities along the boundaries of the forecasts by coordinating with
forecasters at surrounding WFOs and using workstation forecast tools that
identify and resolve some of these differences. The NWS is making progress in
this area, and recognizes that this is a significant issue in which
improvements are still needed. The NDFD was developed by NWS Meteorological
This nowCOAST™ map service is not time-enabled, although it does contain
time-varying data. Instead of supporting the time dimension through use of a
time parameter in each map request, each individual map layer contains data
valid for a different "time offset", or forecast projection, from the dataset's
Due to software limitations, the full temporal resolution (i.e. maximum
forecast horizon and/or all forecast projections) of the data is not provided
by this service. Instead, a corresponding time-enabled service containing the
full temporal resolution is available for this dataset, and users are highly
encouraged to use that service instead, if possible.
This time-offsets map service is provided as a convenience for users who are
not yet capable of interacting directly with the time dimension, especially
users of legacy nowCOAST™ version 4 map services who wish to access the same
data using the new nowCOAST™ version 5 map services. However, this service may
be terminated with little advance notice at a later date.
In addition to ArcGIS Server REST access, time-enabled OGC WMS 1.3.0 access is
is also provided by this service.
In order to determine the latest time information about the data included in
this map service, users have two options:
Issue an Identify (ArcGIS REST) or GetFeatureInfo (WMS) request against
the proper layer corresponding with the target dataset. For raster
data, this would be the "Image Footprints with Time Attributes" layer
in the same group as the target "Image" layer being displayed. For
vector (point, line, or polygon) data, the target layer can be queried
directly. In either case, the attributes returned for the matching
raster(s) or vector feature(s) will include the following:
validtime: Valid timestamp.
starttime: Display start time.
endtime: Display end time.
reftime: Reference time (sometimes reffered to as
issuance time, cycle time, or initialization time).
projmins: Number of minutes from reference time to valid
desigreftime: Designated reference time; used as a
common reference time for all items when individual reference
times do not match.
desigprojmins: Number of minutes from designated
reference time to valid time.
Query the nowCOAST™ LayerInfo web service, which has been created to
provide additional information about each data layer in a service,
including a list of all available "time stops" (i.e. "valid times"),
individual timestamps, or the valid time of a layer's latest available
data (i.e. "Product Time"). For more information about the LayerInfo
web service, including examples of various types of requests, refer to
the nowCOAST™ LayerInfo Help Documentation
- NWS, 2007: National Digital Forecast Database (NDFD) Experimental Gridded Data, Product Description Document,
NWS, Silver Spring, MD (Available at http://products.weather.gov/PDD/NDFDGrids.pdf).
- NWS, 2013: Experimental Gridded Marine Offshore and High Seas Forecasts in the National Digital Forecast Database (NDFD)
Product Description Document, NWS, Silver Spring, MD.
- NWS, 2013: National Digital Forecast Database Element Definition, NWS, Silver Spring, MD (Available at
- NWS, 2014: NDFD Spatial Reference System. NOAA/NWS Meteorological Development Laboratory. (Available at http://graphical.weather.gov/docs/ndfdSRS.htm)
NOAA NWS NDFD Gridded Forecasts of Significant Wave Height (feet) (Time Offsets)
All Layers and Tables
Dynamic All Layers
NOAA/NOS/OCS nowCOAST and NOAA/NWS
Single Fused Map Cache:
Spatial Reference: 102100
Spatial Reference: 102100
[2021/10/12 12:27:00 UTC, 2021/10/15 15:00:00 UTC]
Supported Image Format Types:
Supports Dynamic Layers:
Keywords: marine weather,significant wave height,ocean,Great Lakes,coastal,offshore,bays,harbors,forecasts,gridded,mosaic,seamless,NDFD,NWS,NOAA,Meteorological Development Laboratory,Weather Forecast Office,NCEP,OPC,NHC,TAFB
Supported Query Formats:
JSON, AMF, geoJSON
Supports Datum Transformation: