Use of RTOFS for Current.Gribs - Gulf of Maine

[rgleason]

Also several days ago, I wrote Henri (wr sailgrib) and he said he'd look into trying to get better gribs for the gulf of maine.

[did-g]

Originally Posted by rgleason

I have WR SailGrib will check my oceans, but as did-g points out, and as I tested, the base noaa Hycom do not have tidal currents for Gulf of Maine.

Copernicus *is* MyOcean so no useful data there.

[.Paul.]

Rick and others,

I downloaded surface current forecasts in four West Atlantic Standard GRIB-2 files from NOMADS:

NOMADS-NOAA Operational Model Archive and Distribution System

I went down the page to "Ocean Models" and "RTOFS Global" where I clicked on the "http" box. This brings up a directory with three items:

Parent Directory
rtofs.20170701
rtofs.20170702

I selected the last entry corresponding to today's model run. Then I scrolled down to find each of the lines containing

rtofs_glo_t00x.f???_west_atl_std.grb2

where "???" is "024", "048", "072" or "144" corresponding to the last hour of the forecast in each file. Rather than having the browser download the file, I used the right click to "Copy link". I prefer to use WGET to download files instead of the download routine in the Microsoft browser.

Here is a batch file to get the four files for today's forecast.

wget -N -nd http://nomads.ncep.noaa.gov/pub/data/nccf/com/rtofs/prod/rtofs.20170702/rtofs_glo.t00z.f024_west_atl_std.grb2
wget -N -nd http://nomads.ncep.noaa.gov/pub/data/nccf/com/rtofs/prod/rtofs.20170702/rtofs_glo.t00z.f048_west_atl_std.grb2
wget -N -nd http://nomads.ncep.noaa.gov/pub/data/nccf/com/rtofs/prod/rtofs.20170702/rtofs_glo.t00z.f072_west_atl_std.grb2
wget -N -nd http://nomads.ncep.noaa.gov/pub/data/nccf/com/rtofs/prod/rtofs.20170702/rtofs_glo.t00z.f144_west_atl_std.grb2

This batch drops the files into the currently selected folder on the local machine. Don't run it "as is" without changing the date. This generates four GRIB files. Select all four files at once when opening them in OpenCPN.

The first three files each contain 24 forecast times spaced one hour apart. The fourth file contains 24 forecast times spaced every three hours. Each file is 36 megabytes or just a little larger than the setup file for installing the latest Windows version OpenCPN. Each file download took between 3 minutes 55 seconds and 6 minutes 22 seconds.

Here is a screenshot showing the extent of the West Atlantic current GRIBS.


Here is the northern limit (about 44 degrees 48 minutes north) in the Bay of Fundy.


If you are going to use these current GRIB files with wind GRIBS with the WeatherRouting_pi be sure to open all wind and current GRIBS before computing a route.

Paul

[rgleason]

Dear Paul,
This is great instruction on download of rtofs. Thankyou. I will try it when I am with my computer. The links look good. Can you discern the tidal currents in these gribs? The rtofs I checked recently did not include the Bay of Fundy and Gulf of Maine tidal currents (see below from did-g).
I note that the HYCOM mission statement does include tidal currents near and in shore, however the University of Maine grib model for this very significant body of water has not been incorporated and developed further to my knowledge. With NOAA subject to funding cuts it is unlikely we will see this modeling any time soon.

[rgleason]

Did-g good questions. Race is July 8 - 13. Have not asked u of maine for a grib or atlas if they have the data available in tabular format. Will do so.

[.Paul.]

Originally Posted by rgleason

Dear Paul,
This is great instruction on download of rtofs. Thankyou. I will try it when I am with my computer. The links look good. Can you discern the tidal currents in these gribs? The rtofs I checked recently did not include the Bay of Fundy and Gulf of Maine tidal currents ...

Rick,

Tidal currents are obvious offshore and as far north as the West Atlantic RTOFS model goes (about 27 nautical miles from St John just west of the traffic separation lanes). I see current directions rotating over several hours and with strength changing from 0.0 to 0.7 knot.

Be sure to manually select ALL current and wind GRIBS if you download individual files as I described. The GRIB_pi in OpenCPN only loads the most recent file when it starts.

Paul

[rgleason]

Found these sources of experimental grib files for the gulf of maine.

http://datamirror.org/dataset?tags=gulf+of+maine

[rgleason]

If all of these were concatenated they might be the equivalent of the Gulf of Maine Tidal Current Atlas. Can't wait to get to a computer to try it.

https://data.nodc.noaa.gov/ncep/rtof...50501/surface/

[rgleason]

Dear Paul, I am going to try your script as soon as I get to a computer, and I will upload the StJohn referenced tides, Atlas of Gulf of Maine Tidal Currents as a pdf. I would like you to see the 2.0 to 2.2 currents in and out near the end of Nova Scotia, and Cape Sable. I don't believe any of the rtofs show this kind of current, so I believe the actual Gulf of Maine experimental working model has not been incorporated into rtofs. Until it is properly implimented and calibrated, the tidal currents for this significant body of water will always be inaccurate.

[rgleason]

Please note that these experimental files are not valid grib files.

Originally Posted by rgleason

If all of these were concatenated they might be the equivalent of the Gulf of Maine Tidal Current Atlas. Can't wait to get to a computer to try it.

https://data.nodc.noaa.gov/ncep/rtof...50501/surface/

[rgleason]

The Marblehead to Halifax Race on Summer Wind was lots of fun with a good compatible crew. The skipper provided a good Nmea0183 data connection to the instruments and a Kvh phone which allowed small grib downloads. Moving or walking grib downloads were about 35kb. Immediately before the race we did a full download of the entire racecourse area and all needed data types.

I learned that VPP generated polars will not adequately represent the actual boat speeds possible! I found that using 70% of the wind was closer to reality and that to most effectively use Weather_routing, you must record your own polars at various wind speeds and wave conditions.

I was constantly using Ocpn_Draw to determine and keep track of information, measure & set up EBLS etc.

AIS worked great and was very helpful.

Grib_pi worked well, but I will have a few suggestions to make it easier to make walking or moving gribs from new positions as the race develops.

Also I think Weather_routing needs to make it possible to use the current position of the boat for starting a routing so that as the race develops, the walking gribs downloaded get smaller and include only grib areas starting at the current position and time.

Despite all the preparation, time and effort that went into this race, Summer Wind took 68 hours to complete, she was given little PHRF handicap (13 seconds for the 350 nm race) even though she weighs over 40,000 lbs. The crew was new to to boat and we made some errors, but the real issue on this downwind race was the Asymmetrical Spinnaker would be blanketed when we sailed at lower angles, I don't think we had much asymmetric time at 160 degrees from apparent wind angle, it was always closer to 140-153 degrees, which made our course longer. At 153 degrees we would go 3.4 knots with the asymmetrical and yet at 140 we had decent hull speed. Others following the race noticed that we were always .5 to 1 knot less than the rest of the fleet.

We did have some great night sailing with the moon out and 15 - 20 knots with the boat going 7-8 knots. She is a very powerful boat with adequate wind, but downwind in light air is definitely not her forte. We were very comfortable the entire trip with excellent navigation and safety gear.

For currents, I transfered the Atlas pages with hours from St.John into Opencpn by converting PDF to jpg and using Weather_fax, to overlay with 50% transparency, the appropriate tidal current jpg over the charts to help determine what the tide would be doing. We managed to beat most of the adverse current, but were definitely late in the favorable tidal cycle around Cape Sable and Brazil Rock.

I would have been easier to use grib files or to be able to enter a tabular table with tide velocity and direction, that was expected each hour to operate on the boat.

I will write this up in greater detail later. By the way, OpenCPN generally showed a course close to the rhumbline, although we could not hold that due to the blanketing of the Asymmetrical. I believe the VPP polars calculated greater effectiveness for this sail on low angles than we actually could get. I would have liked to see the route with a better "real world" polar for the boat.

[rgleason]

Ocean Model Current Areas

and now the data is here in a Global model

http://www.nco.ncep.noaa.gov/pmb/products/rtofs/

Goes Satelite derived sea temperatures.
http://www.opc.ncep.noaa.gov/sst/newSST/GOES_SST.shtml

Useful for WxFax

[rgleason]

Here are some other links for Ocean Current OSCAR
https://www.esr.org/research/oscar/data-access/

https://podaac.jpl.nasa.gov/dataset/...4_OC_third-deg

PO.DAAC.LAS.UI

https://podaac-tools.jpl.nasa.gov/la...Y_zoom;view=xy

BlueMarble

https://podaac-tools.jpl.nasa.gov/so...r=500&tlr=days

[rgleason]

This is incorrect, the second page or a back page has the login now, not the front page.

1. Opencpn Grib_pi Downloads using zygrib username and password is no longer available, so this download feature appears to be broken and should be fixed.

[did-g]

Hi,


It seems NOAA is back in coastal prediction:
https://tidesandcurrents.noaa.gov/models.html
https://tidesandcurrents.noaa.gov/of...rents_forecast


but it's a curvilinear grid and netCDF files not grib, ie doable but currently not readable with Opencpn