Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 28-06-2017, 11:07   #31
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

In a last attempt to get a decent 1 hour interval (or 3 hr) grib file for the Gulf of Maine for this race, I am wondering if there is good way to convert hourly interval tide information from a PDF file into a useful current grib file, and adjust the time to High tide at St. John since the current charts are based on high water there.

The files that need to be converted are found onOpenCPN File Thingie rguser, rgpass under the directory "Gulf of Maine Currents"

I would be interested in any suggestions as to how best to do this. Thanks.
__________________

rgleason is offline   Reply With Quote
Old 28-06-2017, 15:47   #32
Registered User

Join Date: Jun 2015
Posts: 302
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Quote:
Originally Posted by rgleason View Post
In a last attempt to get a decent 1 hour interval (or 3 hr) grib file for the Gulf of Maine for this race, I am wondering if there is good way to convert hourly interval tide information from a PDF file into a useful current grib file, and adjust the time to High tide at St. John since the current charts are based on high water there.

The files that need to be converted are found onOpenCPN File Thingie rguser, rgpass under the directory "Gulf of Maine Currents"

I would be interested in any suggestions as to hrtofs ow best to do this. Thanks.
In my understanding there's no tidal current in RTOFS so it's useless for you.

It's possible to convert text to grib with standard tools so once you get current vectors in text adjusting grib time to tide time and range shouldn't be too hard.

Getting speed vectors in text form from a picture? if it's a one-off doing it manually could be the easiest. On the other hand I thing you can buy RTOFS + tides current, likely expensive and quality unknown.
__________________

did-g is offline   Reply With Quote
Old 29-06-2017, 06:20   #33
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

did-g
Thank you for responding. I believe the RTOFS does try to model tidal surface currents.
See About the Atlantic RTOFS down towards the bottom, Atlantic RTOFS, Model Configuration, HYCOM
Surface Forcing -forcing fields from 3-hour NCEP (GDAS/GFS) model
Tides M2, S2, N2, K1, P1, O1, K2, Q1 tidal modes, Body and boundary tides

I believe the 3hour interval exists, but because of recent changes in NOAA due funding, OSCAR no longer works and has moved to NAS and the 1/3 degree model is here

I believe the surface current data with 3 hour intervals exists for the Gulf of Maine, but I don't know how to extract it from the very big files. If you look down below, I think you'll see what I mean.

I am somewhat handicapped in converting the PDF to a grib file because I don't know grib formatting and protocols, and my impression is that to do it by hand would be a big task. I guess it would require some graphic interpreter that could determine the direction of the and degrees in the shaft, and assign magnitude by using the shaft thickness index. This interpreter would have to then output a grib file. It is very unlikely this exists as it is too specific a problem.

I wonder if there is some way to estimate and manually assign current vectors on a larger scale in a grib file, that could at least be used by the weather_routing plugin.
I notice that the hourly currents in the first 2/3's of the race are actually very moderate and that whole area could be assigned (0.5-1.0) in a certain direction for each hour. It is the last third of the leg across that gets critical because the currents go up to 2.2 and if I could make a grib file of that area, assigning manually a somewhat smaller area, for each hour, it would be ideal. Then I would align the date and time with St. John's from July 8 about July 11

PS: Here is an interesting link about an experimental 1/12 degree RTOFS model for the Gulf Stream and Mid Atlantic that just misses the Gulf of Maine.
rgleason is offline   Reply With Quote
Old 29-06-2017, 06:56   #34
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

This bottom link is for "Global RTOFS Model and its use for regional and near coastal modeling at NOAA/EMC". It states NAM is better in some cases than GFS.

OSCAR Data now here
https://podaac.jpl.nasa.gov/dataset/...4_OC_third-deg
rgleason is offline   Reply With Quote
Old 29-06-2017, 07:14   #35
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Here is the experimental 1/12 degree Hycom link.
HYCOM + NCODA Global 1/12 Analysis
rgleason is offline   Reply With Quote
Old 29-06-2017, 07:42   #36
Registered User

Join Date: Jun 2015
Posts: 302
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Quote:
Originally Posted by rgleason View Post
did-g
Thank you for responding. I believe the RTOFS does try to model tidal surface currents.
See About the Atlantic RTOFS down towards the bottom, Atlantic RTOFS, Model Configuration, HYCOM
Surface Forcing -forcing fields from 3-hour NCEP (GDAS/GFS) model
Tides M2, S2, N2, K1, P1, O1, K2, Q1 tidal modes, Body and boundary tides
Yes maybe they have some but if you look at hourly RTOFS or Copernicus' GLOBAL_ANALYSIS_FORECAST_PHY_001_024 they don't have tidal streams you get in your pdf or in OCPN current .

A smaller file from Copernicus data
http://195.154.231.142/HD/maine.grb

Same extracted from RTOFS hourly rtofs_glo.t00z.f024_west_atl_std.grb2
http://195.154.231.142/HD/rtofs_maine.grb

Compare them to your pdf.
did-g is offline   Reply With Quote
Old 29-06-2017, 10:08   #37
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Did-g
You are right! I've checked both an RTOFS (24hour is available not 12hr) downloaded from Saildocs, and the two Hourly Intervals you provided from Copernicus and RTOFS (Those are a good find!). To summarize, I found that the strengths and directions at the end of Nova Scotia are too weak and the directions do not correspond to the the scanned ATLAS OF CURRENTS for Bay of Fundy and Gulf of Maine, using this information for times

http://www.timetemperature.com/tznb/saint-john.shtml

St. John, New Brunswick, CA Atlantic Time Zone (UTC -4)

St. John, is now on Daylight Savings so that also subtracts 1 hour (UTC-3).
UTC - GMT Offset
Saint John, New Brunswick is GMT/UTC - 4h during Standard Time
Saint John, New Brunswick is GMT/UTC - 3h during Daylight Saving Time

Eastern Standard Time is UTC-5
Eastern Standard Daylight Time is UTC-4
So Eastern Standard Daylight Time is one hour greater than St.John

GRIB File is June 29 UTC 12:00
So we subtract 3 hours for St. John Daylight Time = 9:00 am
At St. John Low Tide is 10:54, 2.53ft
Need the table for 1 hour before low water at St. John.

Quote:
Saint John Tide table:
Thursday 29 June
4:36 AM ADT 8.02 meters (26.31 ft) High Tide
5:39 AM ADT Sunrise
10:54 AM ADT 0.77 meters (2.53 ft) Low Tide
Did-g quote
Quote:
A smaller file from Copernicus data
http://195.154.231.142/HD/maine.grb

Same extracted from RTOFS hourly rtofs_glo.t00z.f024_west_atl_std.grb2
http://195.154.231.142/HD/rtofs_maine.grb

Compare them to your pdf.
So it appears that even the 1 hour RTOFS and the 1 hour Copernicus on the half hour that you found, do not represent the actual tidal currents found in the Gulf of Maine as shown by the "Atlas of Tidal Currents".

The current velocities are not even close and directions are off particularly for the last 1/3 of the passage from Marblehead to Brazil Rock, Nova Scotia.

Thank you Did-g, you were right...

Now I wonder if I could take on of these 1 hour grib files from Did-g and edit it to correct the directions and velocities?

Is there a graphic tool somewhere that will let me do that?
I'd like to be able to select a square or polygonal area for a certain hour and then be able to change or edit all those gridded points to be a certain direction and velocity. With a tool like that I could fix on of the grib files for a full cycle of tides.

Then I'd like to find a grib tool that would change the entire grib to a different UTC time so I could get it to align with St. John New Brunswick High and Low Tide.

Perhaps someone can suggest such a tool?
rgleason is offline   Reply With Quote
Old 29-06-2017, 10:39   #38
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Here are some tools for creating and using Grib files https://disc.gsfc.nasa.gov/hydrology...software-tools

WGrib and GrADS are probably the more current software, but I am not sure either one would allow me to simply edit datapoints in a mass way. The tools appear to be more like extraction tools which provide good ways to analyze the data.

Still looking.
rgleason is offline   Reply With Quote
Old 30-06-2017, 05:07   #39
Registered User

Join Date: Jun 2015
Posts: 302
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Quote:
Originally Posted by rgleason View Post
Here are some tools for creating and using Grib files https://disc.gsfc.nasa.gov/hydrology...software-tools

WGrib and GrADS are probably the more current software, but I am not sure either one would allow me to simply edit datapoints in a mass way. The tools appear to be more like extraction tools which provide good ways to analyze the data.

Still looking.
There's also pygrib.

When is your race?
Did you ask Atlas of current producer if they have data in tabular format? Or Maine university?

If you have current vectors in computer readable format, producing grib is not a big problem.
did-g is offline   Reply With Quote
Old 30-06-2017, 14:57   #40
Registered User

Join Date: Oct 2014
Posts: 186
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Rick and others,

Google found this site:

LuckGrib - Home

They seem to have a GRIB downloader for the MAC that is sold on ITunes.

They talk about access to
Code:
RTOFS Global HYCOM. Ocean Currents
which should be of interest for your race.

I am guessing that the LuckGrib people have figured out how to get regional (latitude and longitude) subsets from RTOFS Global.

Paul
.Paul. is offline   Reply With Quote
Old 01-07-2017, 18:31   #41
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Dear Paul. Thankyou. There is not android app and I don't have Mac. Looks good perhaps a mac user can report.
rgleason is offline   Reply With Quote
Old 01-07-2017, 18:34   #42
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

I have exported the Atlas of Currents, created jpg files, and rotated each one, and brought it into wxfax as an overlay. This is atenporary less than optimal solution.
rgleason is offline   Reply With Quote
Old 01-07-2017, 20:09   #43
Registered User

Join Date: Dec 2010
Location: W Carib
Boat: Wildcat 35, Hobie 33
Posts: 9,672
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

Have you tried GRIB current data from MyOceans?

I use it for weather routing and can download it directly via SailGRIB WR (Android).
belizesailor is offline   Reply With Quote
Old 02-07-2017, 05:45   #44
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

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.
rgleason is offline   Reply With Quote
Old 02-07-2017, 05:52   #45
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 11,782
Re: Use of RTOFS for Current.Gribs - Gulf of Maine

The tidal models are available (U of Maine etc) but have not been incorporated into Rtofs model yet.
__________________

rgleason is offline   Reply With Quote
Reply

Tags
current, maine, rib

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
St Lawrence Seaway, Gulf of St Lawrence, Nova Scotia, Gulf of Maine sailing time wind Jm2fly General Sailing Forum 9 11-07-2016 22:53
Avoiding Gulf Stream Current Headed S pete33458 Atlantic & the Caribbean 56 07-09-2015 17:30
RTOFS Gulf Stream Model, Saildocs and Viewfax msulc Navigation 2 08-09-2011 21:08
Gulf Stream Counter Current / Northwest Cuba ? alaskadog Atlantic & the Caribbean 2 22-08-2005 17:51



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 09:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.