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Old 15-04-2014, 05:47   #1
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Improving my gribs

At the moment when I get gribs they are not as up to date as they could be. If I get them in the afternoon then they start at 5.30am local time which is midnight zulu time as I am at zulu + 5 1/2 hours here. If I get them in the morning it's worse - I get gribs from the day before.

I am using sailmail. Of course I have tried changing the time on the grib request window, but that only made it worse! Trial and error hasn't helped so I was hoping to find someone who has worked this problem out already.

I have to admit I used to know how to fix this but after a year off sailing I have forgotten what I used to do.

Your help is much appreciated.

Thanks
Rose
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Old 15-04-2014, 07:17   #2
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Re: Improving my gribs

You do know that GRIB data is only output by the models at synoptic times (00, 06, 12, 18 GMT) right?

Also you can subscribe to a particular GRIB request so that ot it send to you regularly.
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Old 15-04-2014, 09:23   #3
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Re: Improving my gribs

So if they issue it at 0000 GMT, and I get the grib at 0100 GMT, why do I get one that's 25 hours old? I'd like to get one that's only one hour old but I can't figure out how to make that happen.
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Old 15-04-2014, 10:40   #4
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Re: Improving my gribs

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Originally Posted by SailingMum View Post
So if they issue it at 0000 GMT, and I get the grib at 0100 GMT, why do I get one that's 25 hours old? I'd like to get one that's only one hour old but I can't figure out how to make that happen.
Can't find the link now but I think it takes about 4 hours for NOAA to crunch the numbers and send out the gribs. So the latest 06.00 will be available around 10.00
Anyone know for sure?


Edit. Looks closer to 5 hours..
http://nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/

If you scroll down to the gfs files towards the bottom, I think the last 2 numbers are the forecast times, so 00 gets issued just after 5.00 according to the file last modified time.

Sent from my SGP312 using Tapatalk
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Old 15-04-2014, 11:01   #5
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Re: Improving my gribs

Thank you for that. I would never have found or known how to interpret that data. So I take it I can see the grib for 0000 GMT any time after 0500 GMT? I will try that out tomorrow and see if it works.
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Old 15-04-2014, 13:38   #6
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Re: Improving my gribs

IIRC, GRIB files are available very shortly after model run time (synoptic times) because they are direct model output, but other forecast products (such as Weather FAX) are first available up to a few hours later because they require human intervention.

Regardless, your GRIB viewer should show the model run time for the file you receive.

Normally you will receive the most recent GRIB file for a request thru SAILDOCS. Can you paste the text of the request here so we can see what is being sent?

It should look something like this (except probably for the GFS model not COAMPS):

send COAMPS:16N,1N,84W,73W|0.2,0.2|0,6,12..72|=
WIND,PRESS
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Old 15-04-2014, 15:45   #7
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Re: Improving my gribs

> send COAMPS:16N,1N,84W,73W|0.2,0.2|0,6,12..72|=
WIND,PRESS

I don't bother with the "0", just go for "|6,12..72".
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Old 15-04-2014, 20:14   #8
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Re: Improving my gribs

This is what I send:

Subscribe GFS: 22N, 00N, 076E, 100E|0.5,0.5|0,24..72|PRMSL, WIND

I was wondering whether it is because I am subscribing rather than making individual requests (to save minutes on my satphone because otherwise I have to log in once to make the request and a second time to get it). However even when I do it as a request rather than a sub, I still get the old gribs.

Frustrating because I once found a good explanation of this issue on the internet and now I cannot find it again. I have looked all through the sailmail website.

No one wants a twenty five hour old weather forecast!
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Old 15-04-2014, 20:38   #9
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Re: Improving my gribs

"SUB" (or "SUBSCRIBE") should cause the 06Z model output (and only that) to be sent once per day.

"SEND" will cause the most recent model output to be sent.
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Old 15-04-2014, 20:44   #10
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Re: Improving my gribs

Check the actual model run times for the files you are receiving after you send these commands.
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Old 15-04-2014, 21:07   #11
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Re: Improving my gribs

Could you please explain what you mean by "the actual model run times" and where I check these?

Thanks.
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Old 16-04-2014, 07:43   #12
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Re: Improving my gribs

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Originally Posted by SailingMum View Post
Could you please explain what you mean by "the actual model run times" and where I check these?

Thanks.
Its embedded in the GRIB data file, but most viewer apps display it. What GRIB viewer are you running?

Example screen shot of Sail GRIB attached. Look at information window in lower left hand corner for "Model run time".
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Old 16-04-2014, 21:21   #13
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Re: Improving my gribs

OK, so my grib page looks quite different but the first line of my email containing the gribs says:

Grib extracted from file gfs140416-00z.grb dated 2014/04/16 04:38:48

This was from my subscription which I downloaded at zulu 0300 on 17 April, so that is nearly 24 hours old. However, when I tried it as a request rather than a subscription, I got a much more up to date one:

Grib extracted from file gfs140416-18z.grb dated 2014/04/16 22:40:12

This is only 5 hours old.

I guess I am just going to have to send a request each time rather than subscribe, if I want to get reasonably up to date ones.

Oh and thanks StuM, you are right there is no point getting the "0" one as it is already past by the time you get it, and that will save download time too.

Thanks for your help everyone.
Rose
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Old 17-04-2014, 08:47   #14
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Re: Improving my gribs

Yes, there are lots of different GRIB viewers out there. I just used Sail GRIB as an example. Your display will likely be different, but also likely to show the model run time somewhere on the screen.

The SUB only sends the most recent 06Z model run output each day. If you want other model runs then you have to use the SEND command. Looks like that's working for you now.
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Old 07-05-2014, 17:06   #15
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Re: Improving my gribs

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Originally Posted by belizesailor View Post
The SUB only sends the most recent 06Z model run output each day. If you want other model runs then you have to use the SEND command. Looks like that's working for you now.
Or change things around and do your daily download at around 11:00 UTC provided that you have propagation.

That way you'll get the 06:00 GRIB shortly after it is issued and can still use the subscribe..

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