Map Information

This nowCOAST™ time-offsets map service provides maps of the latest nowcasts and forecast guidance of water currents and combined (tides + wind driven) water level from the NOS New York and New Jersey Harbor Operational Forecast System (NYOFS) at 6-hr increments out to 48 hours. Each forecast is valid for the specified forecast projection hour with respect to the latest forecast cycle time (e.g., 0, 6, 12 or 18 UTC). The direction of the water currents are depicted by white streaklets. The magnitude of the current is indicated by the length and width of the streaklet. The surface water currents velocity maps use white streaklets to depict direction on top of different map backgrounds. Two color backgrounds are available: speed of currents and water level. For speed, a color scale from black to gray is used to depict speeds from 0 to 4 knots at 0.5 knot increments, except for 0.25 knot intervals from 0 to 0.5 knots. For water level, a color scale from pink to red is used to depict water levels from -14 ft to +12 ft at mainly 0.5 ft increments. The water levels are referenced to the OFS model sea level and not to MLLW, MSL, or NAVD88. The maps of NYOFS forecast guidance 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.

Background Information

NYOFS is based on the Princeton Ocean Model (POM), a terrain following numerical ocean or hydrodynamic prediction model. The OFS grid domain covers Port of New York and New Jersey and the lower Hudson River in a nested-grid configuration. A high-resolution grid is embedded within and dynamically connected to a coarse grid to provide detailed current shears and eddies in the navigation channels of the Kill Van Kull. The spatial horizontal resolution of the coarse and fine grids are approximately 350-1000 m and 120-250 m, respectively. It has four forecast cycles per day (0500, 1100, 1700 and 2300 UTC) which generate forecast guidance out to 48 hours. The forecast cycle uses 3-hourly surface wind forecast guidance from NCEP North American Mesoscale (NAM) model (12 km resolution) for surface meteorological forcing. For forcing at the lateral ocean boundary, the OFS uses sub-tidal water level forecast guidance from the NWS Extratropical Storm Surge (ETSS) Model along with NOS tidal harmonics. Each forecast cycle is preceded with a 6-hr long nowcast cycle. The final nowcast serves as the initial conditions for each forecast cycle. The nowcoast cycle is driven by near-real-time water levels and surface wind velocities from the observing stations of the NOS Physical Oceanographic Real-Time System (PORTS). NYOFS was developed and evaluated by the NOAA/NOS Coast Survey Development Laboratory Coastal Marine Modeling Branch in collaboration with the NOS Center for Operational Oceanographic Products and Services (CO-OPS). NYOFS is run on Linux servers operated by CO-OPS. For more information, please see http://tidesandcurrents.noaa.gov/ofs/nyofs/nyofs.html.

The maps are generated using a visualization technique developed by the Data Visualization Research Lab at The University of New Hampshire's Center for Coastal and Ocean Mapping (http://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 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 reference time.

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:

1. 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.
2. 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

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.
• Wei, E., 2003: The new Port of New York and New Jersey Operational Forecast System (NYOFS), Bull. Amer. Meteor. Soc., 1004-1006.