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nowcoast/guidance_model_coastalocean_sjrofs_offsets (MapServer)

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Service Description:
Last Revised: February 2016

Map Information

This nowCOAST™ time-offsets map service provides maps of the latest nowcasts and forecast guidance of surface water temperature, salinity, and water currents and also total (tides + wind driven) water level from the NOS St. Johns River Operational Forecast System (SJROFS) 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). Forecast guidance is available from the mouth of St. Johns River at Mayport upstream to Buffalo Bluff, FL. The surface water currents velocity maps display the direction using white or black streaklets depending on the color background. Four color backgrounds are available: sea surface water temperature, surface salinity, speed of currents, and water level. For water temperature, a color scale from dark blue to medium orange is used to display temperatures from about 28 degrees F to 88+ degrees F at 2 degree increments. For salinity, a color scale from black to dark red is used to display salinity values from 0 to 40 ppt at 4 ppt increments. Colors were chosen to highlight approximate thresholds for freshwater, brackish water, and saline waters. 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 SJROFS 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

SJROFS is based on the Environmental Fluid Dynamics Code (EFDC), a terrain following numerical ocean or hydrodynamic prediction model similar in many ways to the Princeton Ocean Model. The OFS grid domain covers St. Johns River and immediate continental shelf near the mouth. SJROFS is a 3-D forecast modeling system with a spatial horizontal resolution ranges from approximately 81 m to 2 km and 6 terrain following or sigma vertical levels. It has an hourly nowcast cycle and 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 forecast guidance of surface winds and sea level pressure from NCEP North American Mesoscale (NAM) model (12 km resolution) for the POM surface meteorological forcing. For forcing at the lateral ocean boundary, the OFS uses a set salinity of 35 psu at the surface and 36 psu at the bottom and water levels based on superposition of sub-tidal water level forecast guidance from the NWS Extratropical Storm Surge (ETSS) Model with the NOS tidal harmonics at Mayport, Florida. For river boundary conditions, the OFS uses near-real-time discharge observations from USGS river gages along 6 tributaries. 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 surface winds from the NOS automated weather station at Mayport, FL, persisted river observations, and slightly adjusted near-real-time water level observations from the NOS tide gage at Mayport. SJROFS 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). SJROFS became operational in September 2005. SJROFS is run on CO-OPS Linux servers. For more information, please see

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 ( 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


Map Name: NOAA NOS St. Johns River Operational Forecast System (SJROFS) Forecast Guidance (Time Offsets)


All Layers and Tables

Dynamic Legend

Dynamic All Layers

Layers: Description:


Spatial Reference: 102100  (3857)

Single Fused Map Cache: false

Initial Extent: Full Extent: Time Info: Units: esriMeters


Document Info: Supports Dynamic Layers: true

MaxRecordCount: 1000

MaxImageHeight: 4096

MaxImageWidth: 4096

Supported Query Formats: JSON, AMF, geoJSON

Min Scale: 0

Max Scale: 0

Supports Datum Transformation: true

Child Resources:   Info   Dynamic Layer

Supported Operations:   Export Map   Identify   Find   Return Updates