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Old 13-05-2021, 04:44   #1
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Don't know who to believe!

Hi all. Hoping to get a better idea on these wx apps and their forecast models. I am currently at anchor in Matthewtown, Bahamas waiting on a wx window to go to Luperon, Dominican Republic. 170nm distance so requires 2 nights and a day if I want to arrive in Luperon in early morning (as recommenced by Bruce Van Sant). I have been watching the Windy app with ECMWF forecast model which to me suggests leaving tomorrow night for a Sunday morning arrival. I just downloaded the Predictwind app and looked at both the PWG and PWE models and they are vastly different than the ECMWF model and suggest light variable winds between Great Inagua and Luperon. This is our first time cruising these grounds and will be our first time to DR. Can any of you salty sailors out there help me out here? Hoping for some Clarity (get it?) Thanks in advance.
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Old 13-05-2021, 04:55   #2
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Re: Don't know who to believe!

That's frustrating. My answer, long ago, was to start with the best available data, not the best prediction, and form my own judgement. Doing that let me make much more specific predictions about tornados and straight line cells, and when to shut down my university, than could NOAA/NWS. Extending that to cruising means forming my own judgement about conditions in the Gulf of Mexico where we play. I use WeatherTap.com, complete with the cells, and yesterday sent a text to our county emergency management that the front about to hit us did not scare me because of the low cloud tops and low cell velocities. On the other hand, they could expect very heavy rain.

I'm rambling a bit. Central to my thinking is that you go for good data, and modify the predictions you get by your own judgement, as opposed to always trusting one but not the other.
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Old 13-05-2021, 05:09   #3
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Re: Don't know who to believe!

Thanks tkeithlu. The only real data I'm likely to get for this area is real-time wx report from someone already out in the middle ground between here and Luperon to see if actual wind/wave corresponds to any of the models. Or a wx buoy out there, but I don't know of any.
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Old 13-05-2021, 05:11   #4
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Re: Don't know who to believe!

This is the fun part of trying to be meteorologist. Those PWG and PWE models are proprietary. They're based on the same initial conditions as some of the big boy models (PWE is based on data collected for the ECMWF or European model and PWG is based on the data collected for the GFS model). However, what their models do with the data might be completely different. No one weather model is going to be 100% right. This is where you'll have to step in and try to see why they're coming up with two different solutions. Is one model forecasting a front to stall out to the north? Is one model faster or slower with it? Eventually all models should converge on the same solution, so it might take a couple more model runs to see if they start to agree. Usually i find if more than one model is consistently trending in one direction, that's probably the correct one. You could always give it another day and see if they finally start to agree. Unfortunately some models are also ok with the big picture but horrible when it comes to local conditions.
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Old 13-05-2021, 05:12   #5
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Re: Don't know who to believe!

I am a fan of good old-fashioned surface analysis charts and any local weather forecasts I can get. An expert forecaster has looked at all of the data available and come up with a best guess of what will happen. Do you have access to Chris Parker's broadcasts? He is very knowledgeable about Caribbean weather?
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Old 13-05-2021, 05:16   #6
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Re: Don't know who to believe!

Thanks Enrique100. We are not in a hurry to go out and have a miserable trip. Initially were planning on leaving tomorrow night using windy's ecmwf and PWG /PWE still show that a Sunday morning arrival is good also, so at worst we sit around for one day more than necessary.
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Old 13-05-2021, 05:37   #7
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Re: Don't know who to believe!

Quote:
Originally Posted by Nightsky View Post
Initially were planning on leaving tomorrow night...
Never start a passage on a Friday!
(Old Sailor's superstition)
(You did request salty responses...)

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Old thread:
Red or Green...? Sailor's Superstitions
https://www.cruisersforum.com/forums...ns-234285.html
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Old 13-05-2021, 05:41   #8
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Re: Don't know who to believe!

Quote:
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...Do you have access to Chris Parker's broadcasts? He is very knowledgeable about Caribbean weather?
Thanks AiniA. Unfortunately my SW reciever picks his broadcast up so poorly that I cannot make out his words, only that he is there.
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Old 13-05-2021, 05:46   #9
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Re: Don't know who to believe!

Quote:
Originally Posted by LittleWing77 View Post
Never start a passage on a Friday!
(Old Sailor's superstition)
(You did request salty responses...)

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Old thread:
Red or Green...? Sailor's Superstitions
https://www.cruisersforum.com/forums...ns-234285.html
Thanks for that salty advice, LittleWing. That is one that I never heeded when I was a commercial fisherman. Not superstitious at all. In fact, in those days I didn't even heed wx forecasts as they were usually overcautious and I would lose fishing days if I did. Now I am more of a wx weenie. I tell myself it is because I don't want to subject my wife to crummy conditions and have her want to stop cruising.
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Old 13-05-2021, 06:00   #10
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Re: Don't know who to believe!

Quote:
Originally Posted by tkeithlu View Post
That's frustrating. My answer, long ago, was to start with the best available data, not the best prediction, and form my own judgement. Doing that let me make much more specific predictions ...
Many of us may not be as confident, as you, in our abilities to outperform the professionals.
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Old 13-05-2021, 06:27   #11
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Re: Don't know who to believe!

Quote:
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Now I am more of a wx weenie...
LOL!

You said it, I didn't.

Well, if you used to be a commercial fisherman, you know how to read the NOAA surface charts (google "NOAA current surface maps") reflecting the location of highs and lows and various barometric pressures of each - then draw your own conclusions.

I'm with Keith (Post #2): "Believing" in some algorythmic weather-prediction programme is ineffective long-term and ultimately, will blunt your own seamanship.

If you're a fisherman, perhaps make a point of searching out and talking to some local fisherman. Now there's a great source of local weather knowledge...!

Fair winds,
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Old 13-05-2021, 06:44   #12
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Re: Don't know who to believe!

It is unusual that weather models are very different from each other just one or two days out. I have found the PWG and PWE models to be good in the short run, but less helpful more then 3 or 4 days out. While the European Model has been my goto, if it is the outlier from the other 3 major models I review (GFS, SPIRE, UKMO), I get suspicious and careful.

A general rule is that if the models show a great deal of difference, the forecast, even by the professionals, will have a high degree of uncertainty. That's just the nature of weather. If all the models line up nicely, then the consensus has a high likelihood of accuracy. That "uncertainty factor" is something you miss if the only thing you look at are surface charts.

If you have predictwind, why have you not downloaded the GMDSS text forecasts to see what the professional forecasters think? Either windy or predict wind can give you current observations if you are concerned about what is happening NOW.

Having spent a lot of time comparing surface charts to model data, I find the differences in information content to be trivial when the models are well aligned. Any forecast 96 hours out is a fantasy no matter if it is a model or a professionally hand drawn chart.
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Old 13-05-2021, 06:52   #13
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Re: Don't know who to believe!

Far as i have been able to tell the only time you can be sure the weather forecasters will be right is when they say it will be bad!

My trip from bahamas to stayes last month was terrible. Yeah the forecast said it was 1’ waves every 10 seconds. Even when i got into vhf range for the weather they saying that. I guess there were 1’ waves every 10 seconds, mixed in with the 5’ waves every 2 seconds
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Old 13-05-2021, 07:03   #14
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Re: Don't know who to believe!

While the charts and graphs are all very nice, I very much rely on getting the NWS text products as well because they can give you the thoughts of an actual trained forecaster. They do differ by area, up here in Juneau the forecast discussion talks about each model, how they differ, and why the forecaster selected a particular one or made his/her own amalgam. And sometimes different forecasters argue back-and-forth in the discussions.

For the tropical Atlantic the products I found donít seem quite as robust, but I would still add them to my arsenal because they are human written and the models arenít quite there yet. Once you get familiar with them you can get to know the forecasters and use your own observations to believe some more than others (the forecasterís name is at the bottom).

https://www.nhc.noaa.gov/text/MIAOFFNT3.shtml
https://www.nhc.noaa.gov/text/MIATWDAT.shtml
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Old 13-05-2021, 07:57   #15
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Re: Don't know who to believe!

Why not follow The Thornless Path to Windward and then you can day sail almost the whole way. Lovely cruising grounds too.
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