Zezo forum:

Post by chelonia | 2017-11-08 | 12:34:07

Am I correct that wind/weather updates are regular in the game i.e. unknown. And Zezo updates CET: 02:00, 06:00, 13:00. and 19:00.

Much appreciated

21 Comments

Post by zezo | 2017-11-08 | 14:30:45

This post is long overdue, so here it comes:

Weather is updated 4 times/day. The update is incremental and new data is added as it becomes available from NOAA (both the game and here)

The schedule begins at 9:30 UTC (10:30 CET in winter) with 12 hours of data, then 24 hours worth of forecast are added every 10 minutes or so. At 10:30 UTC the first week is available. The full 384 hour forecast is available at 11 UTC.

The same process repeats every 6 hours.

The game seems to be using interpolation between the old and the new forecast for a while, and I just use the old one for 1 hour and the new one afterwards. That may lead to visible differences around 11 - 12 UTC if the two models differ too much. In such cases it's probably better to sail in the general direction where the router is leading you, if possible (optimum TWA otherwise)

When to check the routing depends on the duration of the desired track. On the final stretch it might be worth checking the track as early as 9:32. On a 16-day forecast using half old and half new data may be quite misleading sometimes, so you better wait until 11UTC

Post by bourgeron | 2020-11-10 | 18:06:23

Hi,

It's an old post, but is still the way it goes in 2020 ?

Thx !!

Post by chelonia | 2017-11-08 | 15:30:24

Thank you so much Cvetan!!!

Post by chelonia | 2017-11-08 | 15:49:02

So in laymen terms (based in EU), we check Zezo shortly after 10:30, 16:30, 22:30, and 04:30 for new routing based on the new weather data, and this will give us am updated 12 hour weather window.

And every day at 12:00 CET the full (1-16) day forecast is updated in Zezo, altough it becomes gradually visible in the game during the 10 minute intervals after every start of the schedule (10:30, 16:30, 22:30, and 04:30).

Post by zezo | 2017-11-08 | 16:18:35

The weather here is also updated gradually in 10-15 minute interval.

You mach check the popup info when you hang the mouse in the GFS field in the status bar. But it seems to be a bit broken because of the 16-day change. Will have to check it again.

Post by Ursus Maritimus | 2017-11-08 | 17:34:03

Thanks for the detailed info on weather updates, Svetan. There seems to be a discrepancy between the charts and updates regarding CET time of updates:

If I look at the timestamp on the thick lines on the charts (that suggest weather updates), the time indicated is 19:00 CET and 2:40 from now (16:30 CET).

Since dailight savings is over since a few weeks, there is only one hour difference between UTC and CET. That is what you use in your explation in this topic.

So the next completed weather update is at 18:00 CET, right? On the charts it says 19:00 CET.

Post by zezo | 2017-11-08 | 17:49:53

The thick lines do not signify weather updates. They are 6 hours apart and synced with the weather model data.

GFS runs like this (times in UTC)

at 00h observations are made all around the globe and all data is gathered and fed into the NOAA supercomputers. They have to build a model of what's actually happening based on the limited data and that takes time. The fist output is not a forecast, it's analysis of the (now past) starting weather conditions.

The first output which is actually a forecast (concerns point in the future) is actually for t=06h (that's called GFZ 00Z+6) and it becomes available at actual time 3:30 UTC (+3h is past moment now). Then calculations continue with oputput for every 3 hours (thats gfs0z+9, 12, 15 ...)

Thick lines correspond to those moments in time. As a visual hint the forecast is ready 1 line before the thick one.

Post by Ursus Maritimus | 2017-11-08 | 17:58:29

aha, that clarifies the delta. thanks!

Post by sudoeste | 2017-11-11 | 22:18:56

Hello Cvetan

We're currently having a big difference (24�) in wind direction between the game and zezo.

Have you detected the reason and can you match the two, so not to affect predicted routes.

Thanks

SW

Post by zezo | 2017-11-11 | 22:37:57

You look fine from my point of view. Sure you got the right numbers in?

Post by sudoeste | 2017-11-11 | 22:40:25

Hello again

Never mind.

The problem was in the game. It was showing me the old wind and giving me a TWA against the old wind, but moving the boat with the new wind. I logged off and on again and I have the correct wind and, as I had auto WA on, my boat was sailing 20� off the pretended course.

SW

Post by Ursus Maritimus | 2017-11-13 | 23:07:34

Cvetan, this explains how weather updates are done en zezo.org.
Do you know how weather is updated in VR?

With the VR Dasboard in use for logging , I would expect to be able to see an abrupt weather change when the update it, but I don't see it happing near where my boats are in all four races.

My tjv and vor are pretty close by the way. With the first version you could even see the distance in nm and that was at times <100 nm ...

Post by zezo | 2017-11-13 | 23:20:48

It's not abrupt because the fist change is 2.5 hours away when it comes out, and only 15% of the current weather is affected by it. Additionally VR does interpolation between the old and new data 2.5 hours ahead, so even if the new forecast is radically different (like wind blowing in opposite direction) you may see abrupt change but it will be less than 10%.

The past weather never changes.

Hope that clarifies it a bit.

My first post already states that, but it's very hard to explain or understand if you have not spent 10 years looking at grib files daily.

Post by Ursus Maritimus | 2017-11-14 | 01:03:53

I trust you at your word ;)

Post by kallemans | 2018-01-01 | 11:25:21

Does the windforecast change over the 6 hours, after its full updatet? Ex. half an hour before the next update at 1030 CET.

Post by karriv | 2018-01-17 | 10:27:04

My observations on the wind behavior in the game would suggest that VR updates the winds as soon as they are available from NOAA, using an interpolation between the old winds and the new winds. On a number of occasions in the past days (in the doldrums), the new forecast has been a major change to the older one, so the change has been quite visible. My observations would suggest this new interpolated wind is in the game at 09:30 UTC (+n*6 hrs).

Post by zezo | 2018-01-17 | 11:20:38

Exactly. The wind we see between 9:30 and 12 is interpolated between 3 values - 0z+9, 0z+12 and 6z+6 and the balance between 0z+12 and 6z+6 also depends on the time.

I was going to park a boat at integer coordinates somewhere in the doldrums and check the calculations, but did not have much time recently, and it's a bit complicated because the temporal interpolation is done over u/v wind components

Post by Rupert | 2019-03-21 | 18:12:51

I would like to know which forecast model you use please ?

Post by zezo | 2019-03-22 | 11:20:00

GFS. The only one available for free, so everyone uses that ;-)

Post by DonJuan21 | 2019-05-24 | 15:55:50

Except predictwind.com. You can get a route there using different models. But it's expensive. They offer GSF, ECMWF, and two of their proprietary models, PWG and PWE.

Post by zezo | 2019-05-29 | 19:49:05

It's expensive because they pay about $100000/yr to access the ECMWF data and computing resources, and the cost has to be shared by end users. It's worth it in real life, of course.