Map Information
This nowCOAST time-enabled map service provides maps depicting the latest global forecast guidance of water currents, water temperature,
and salinity at forecast projections: 0, 12, 24, 36, 48, 60, 72, 84, and 96-hours from
the NWS/NCEP Global Real-Time Ocean Forecast System (GRTOFS). The surface water currents velocity maps displays the direction using
white or black streaklets. The magnitude of the current is indicated by the length and width of the streaklet.
The maps of the GRTOFS surface forecast guidance are updated on the nowCOAST map service once per day. For more detailed information about the update schedule, see: https://new.nowcoast.noaa.gov/help/#section=updateschedule
Background Information
GRTOFS is based on the Hybrid Coordinates Ocean Model (HYCOM), an eddy resolving, hybrid coordinate numerical ocean prediction model.
GRTOFS has global coverge and a horizontal resolution of 1/12 degree and 32 hybrid vertical layers. It has one forecast cycle per day
(i.e. 0000 UTC) which generates forecast guidance out to 144 hours (6 days). However, nowCOAST only provides guidance out to 96 hours (4 days).
The forecast cycle uses 3-hourly momentum and radiation fluxes along
with precipitation predictions from the NCEP Global Forecast System (GFS). Each forecast cycle is preceded with a 48-hr long nowcast cycle.
The nowcast cycle uses daily initial 3-D fields from the NAVOCEANO operational HYCOM-based forecast system which assimilates situ profiles
of temperature and salinity from a variety of sources and remotely sensed SST, SSH and sea-ice concentrations. GRTOFS was developed by
NCEP/EMC/Marine Modeling and Analysis Programs. GRTOFS is run once per day (0000 UTC forecast cycle) on the NOAA Weather and Climate Operational Supercomputer System
(WCOSS) operated by NWS/NCEP Central Operations.
The maps are generated using a visualization technique was developed by the Data Visualization Research Lab at The University of New Hampshire
Center for Coastal and Ocean Mapping (https://www.ccom.unh.edu/vislab/). The method combines two techniques. First, equally spaced streamlines are computed
in the flow field using Jobard and Lefer's (1977) algorithm. Second, a series of "streaklets" are rendered head to tail along each streamline to show the
direction of flow. Each of these varies along its length in size, color and transparency using a method developed by Fowler and Ware (1989), and later
refined by Mr. Pete Mitchell and Dr. Colin Ware (Mitchell, 2007).
Time Information
This map is time-enabled, meaning that each individual layer contains
time-varying data and can be utilized by clients capable of making map requests
that include a time component.
This particular service can be queried with or without the use of a time
component. If the time parameter is specified in a request, the data or imagery
most relevant to the provided time value, if any, will be returned. If the time
parameter is not specified in a request, the latest data or imagery valid for
the present system time will be returned to the client. If the time parameter
is not specified and no data or imagery is available for the present time, no
data will be returned.
In addition to ArcGIS Server REST access, time-enabled OGC WMS 1.3.0 access is
also provided by this service.
Due to software limitations, the time extent of the service and map layers
displayed below does not provide the most up-to-date start and end times of
available data. Instead, users have three options for determining the latest
time information about the service:
Issue a returnUpdates=true request for an individual layer or for
the service itself, which will return the current start and end times of
available data, in epoch time format (milliseconds since 00:00 January 1,
1970). To see an example, click on the "Return Updates" link at the bottom of
this page under "Supported Operations". Refer to the ArcGIS REST API Map Service Documentation for more information.
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
time.
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 help documentation at:https://new.nowcoast.noaa.gov/help/#section=layerinfo
References
Fowler, D. and C. Ware, 1989: Strokes for Representing Vector Field Maps. Proceedings: Graphics Interface '98 249-253.
Jobard, B and W. Lefer,1977: Creating evenly spaced streamlines of arbitrary density. Proceedings: Eurographics workshop on Visualization in Scientific Computing. 43-55.
Mitchell, P.W., 2007: The Perceptual optimization of 2D Flow Visualizations Using Human in the Loop Local Hill Climbing. University of New Hampshire Masters Thesis. Department of Computer Science.
NWS, 2013: About Global RTOFS, NCEP/EMC/MMAB, College Park, MD (Available at https://polar.ncep.noaa.gov/global/about/).
Chassignet, E.P., H.E. Hurlburt, E.J. Metzger, O.M. Smedstad, J. Cummings, G.R. Halliwell, R. Bleck, R. Baraille, A.J. Wallcraft, C. Lozano, H.L. Tolman, A. Srinivasan, S. Hankin, P. Cornillon, R. Weisberg, A. Barth, R. He, F. Werner, and J. Wilkin, 2009: U.S. GODAE: Global Ocean Prediction with the HYbrid Coordinate Ocean Model (HYCOM). Oceanography, 22(2), 64-75.
Mehra, A, I. Rivin, H. Tolman, T. Spindler, and B. Balasubramaniyan, 2011: A Real-Time Operational Global Ocean Forecast System, Poster, GODAE OceanView –GSOP-CLIVAR Workshop in Observing System Evaluation and Intercomparisons, Santa Cruz, CA.
