Zezo forum: predicted time

predicted time

Post by ferrocime | 2019-05-15 | 15:39:36

what is : 15.5 06z 00z 18z 12z etc????

18 Comments

Post by tchoa860 | 2019-05-15 | 16:55:27

the same to me , I dont undestand very well the predicted time ?

Post by ferrocime | 2019-05-15 | 17:21:49

BONSOIR, QUE VEUT DIRE LA PREMIERE LIGNE DU TABLEAU "PREDICTED TIME" COMPOS�E DE CASES 15.5 06z ETC
Je ne parle pas anglais et votre page ne supporte pas mon traducteur google !!!!!!!!

Post by Eldian | 2019-05-18 | 09:20:29

Bonjour,
je donne l'explication en Fran�ais ;)

GFS c'est le mod�le de pr�vision

ensuite la premi�re ligne d'entete donne les date et heures des pr�visions m�t�o utilis�es pour le calcul.
Donc la 1�re colonne donne l'heure de d�part UTC (z = heure zoulou ou UTC).
Et il faut lire la ligne, en me basant sur les pr�vision meteo du jj.m hhz (colonne) en partant � la date et heure de cette ligne jj.m hh:mm, je fais le parcours en x heures, et ainsi de suite pour chaque colonne.

Je ne sais pas si ma formulation est bien claire ?

Bons vents avec zezo ;)
Eldian

Post by zezo | 2019-05-15 | 17:35:44

The

15.5 15.5
12z 06z

should be read as:

According to the forecast from 15th of May, GFS model 12z, it will take X hours (in the cell below) to reach the destination, if the start time is (row with date)

Post by ferrocime | 2019-05-15 | 17:36:57

Start at 15.5
06z 15.5
00z 14.5
18z 14.5
12z 14.5
06z 14.5
00z 13.5
18z 13.5
12z 13.5
06z 13.5
00z 12.5
18z 12.5
????????????????????????????????????????????????????????????????????????

Post by ferrocime | 2019-05-15 | 17:40:05

GFS model 12z O ooooohhhhhh ?????????

Post by zezo | 2019-05-15 | 17:49:19

GFS is the name of the computational forecast model.

12z means "weaher forecast with starting conditions based on observations at 12 hours UTC (noon) that day", data is ready few hours later.

There are other forecasts besides GFS, but they are either not global or very expensive.

Post by ferrocime | 2019-05-15 | 18:21:14

Oooooooooooooookay many thanks amigo !!!!!!!!!!!!!!!!

Post by tchoa860 | 2019-05-15 | 21:38:03

Thank's Zezo , now i undestand better !

Post by CapKermit | 2019-05-16 | 22:18:38

"z" mean zoulou. zoulou is UTC. In France the summer time is in "bravo" (UTC+2), and the winter time is in "alpha" (UTC+1)

Post by MJPullen | 2020-07-14 | 08:18:56

Hi. I'm fairly new to VR and this site. I'm looking to time my next attempt across the Atlantic and want to check whether I understand the assumptions used on the Predicted Times table, particularly the timing of the modelling across the top.

Does the modelling take place every six hours and the duration data is calculated using the latest three day's forecast conditions, with the most recent modelling in the left hand column?

Accepting inherent unpredictability in forecasts, is the most recent predicted time the most reliable?

Post by BooBill | 2020-07-14 | 10:10:36

Yes.

As each new forecast is generated it populates the left-hand column and previous forecasts are shifted to the right. It's provided to show you the evolution of a window over time and to crush your spirit as good opportunities fade as they approach.

Post by MJPullen | 2020-07-14 | 10:30:32

Great. Makes perfect sense.

I did see that for some of the rows there is a rhythmic increase and decrease in the predicted time over a twelve hour period. What could cause that? Day/night starting conditions resulting in a large difference at the finish?

Post by BooBill | 2020-07-14 | 12:52:45

Day/Night land effects can affect the start and finish. However, it's more the movement of synoptic systems. There's an ideal time to catch one and ride it all the way across the Atlantic.

For the Atlantic crossing, you are looking for a low pressure system crossing the continent passing north of NY. That will give you a reach in SW winds at the start and if you play it right you can stay just ahead of the front and ride it the whole way across.

Start too soon and you could run out the front of the system. Start too late and the window closes.

Post by YourMomSA | 2020-07-14 | 14:25:31

Regarding the crushing of spirits as approaching opportunities fade... I think that has something to do with the nature of the GFS model. Forecasts further into the future are modeled with wider increments. If a large system is in a nice spot with a 12-hour duration, it can produce a faster run projection than if it moves from less ideal locations into and out of that spot over time. As the forecast becomes more current, the model includes more realistic movement of that system, which can become less optimistic. I'm not sure if I'm right or not, but that's my theory. Particularly when the predicted times table is showing a sudden great time that only lasts for a few hours... If it's a wide window where a whole day looks good, then this situation is less likely to be crushed.

I suppose it can also work out the other way... If you have to navigate a light patch at the start or finish, increased granularity of the forecast may help to establish faster routes through the quagmire. But... if a route has much of this in it, then it probably isn't going to be a great route anyway.

In other words, I think the "predicted times" table is prone to more extremes (both good and bad) further out, and then settles toward mean as it becomes current.

Post by BooBill | 2020-07-14 | 15:04:32

The "crushing your spirit" comment was personal. As a long time NYC resident, Hamptons weekender and sailor I can't tell you the number of times a great forecast for strong southwesterlies fizzles.

It's all to do with the position of the low pressure as it moves offshore. Great predicted times can fizzle and vanish if that SW doesn't get to the shore. You are stuck on the inside and can't get to the wind offshore. That's also how I became pretty good at golf.