[Amel Yacht Owners] Re: Predict Wind


Patrick McAneny
 

Bill , You should work for PW , you better explained the models and how the forecast are derived than their contact reps did. It still concerns me how inaccurately the winds are predicted. I will have to assume that all wind predictions may well be underestimated by a considerable degree.Thanks for your time to explain.
Pat 
SM#123


-----Original Message-----
From: greatketch@... [amelyachtowners]
To: amelyachtowners
Sent: Wed, Sep 12, 2018 7:11 pm
Subject: [Amel Yacht Owners] Re: Predict Wind

 
Pat,

PredictWind has four different models that it presents.  The first two are the GFS and ECMWF which are the two major worldwide weather models.  Nothing about these models is special to PredictWind, these are exactly the same two models that virtually EVERY weather forecast agency all over the world uses. ECMWF tends not to show in many "free" weather programs because you have to buy the results from the European Center for Mid-range Weather Forecasting.  The output from the GFS model is free to all from NOAA.

The other two models are the PWG and PWE are the PredictWind's "enhanced" versions of the output from the GFS and ECMWF models. I have not found them to be significantly more helpful than the actual model outputs.  I do not understand exactly what PW does to create this output from the major models.

In comparing model outputs to the & quot;real world" data, there are many things that can make them look different.  Starting with the fact that the most violent parts of a very large hurricane are actually a rather small weather feature on a global scale. 

PredictWind averages conditions over significant areas, and this can significantly impact the numbers.  In the highest resolution data available from PredictWind it still averages data over 50km.  That is a very large area when you are talking about a hurricane, where the highest winds are in a very narrow band around the eye.  To take this to an extreme example, PredictWind can not tell you about the wind speed in a tornado, it is too far small.  It's the same with a hurricane, although it obviously does better.

The GFS model itself only works internally to a resolution of 28km.  ECMWF model works at a higher resolution internally (9 or 10km, I think). So the models actually calculate a LOT more data than PredictWind presents, but they are still an approximation--at best--of what a real hurricane looks like.

Another issue is that it is not always clear about what wind number we are actually talking about.  Is the the 1 minute average?  the 3 minute average?  the surface wind?  The wind at 10 meter elevation?  All these numbers can be very different.  I don't know which of these numbers PredictWind presents.  I don't really care, for the way I use the program.  Many times the m edia presents the biggest number they can find because they sell more advertising that way.

I always caution people when they look at GRIB files created by computer programs. They look so PRECISE, it is so tempting to trust them.  They have none of the caveats that and weasel words that come from weather forecasters.  But these are NOT weather forecasts, and they are NOT reporting current conditions... they are the inputs that are used to create weather forecasts.  

Bill Kinney
SM160, Harmonie
Annapolis, MD, USA

---In amelyachtowners@..., wrote :

I bought Predict Wind a few months ago and  a Iridium G o to download offshore. I found it to under report winds with TS Gordon by a large margin,like 50%. Now with the Hurricane Florence and sustained winds of Cat4 140 mph reported for the last two days ,Predict Wind is showing from 68mph on PWG to 102 mph on GFS. Since this is a well reported storm I don't understand the under reported wind speed . Is PW generally this far off, can it be relied on? I asked PW about this and basically they said , that their models are"not geared to predicting hurricanes." I do not understand this explanation , a hurricane is simply a low pressure system, their models are not geared to predict low pressure systems ? I have been looking at their models and comparing them with known conditions. So far it is not reassuring , has it been found to be reliable ?
Thanks,
Pat
SM#123


Peter Forbes
 

This forum is just nothing short of very impressive for this sort of knowledge and comment. It makes me want to take Carango off the market and go sailing again.

Thank you.

Peter Forbes
Carango
Amel54#035
La Rochelle
00447836 209730

On 13 Sep 2018, at 01:01, Patrick Mcaneny sailw32@... [amelyachtowners] <amelyachtowners@...> wrote:

 

Bill , You should work for PW , you better explained the models and how the forecast are derived than their contact reps did. It still concerns me how inaccurately the winds are predicted. I will have to assume that all wind predictions may well be underestimated by a considerable degree.Thanks for your time to explain.

Pat 
SM#123


-----Original Message-----
From: greatketch@... [amelyachtowners] <amelyachtowners@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Wed, Sep 12, 2018 7:11 pm
Subject: [Amel Yacht Owners] Re: Predict Wind

 
Pat,

PredictWind has four different models that it presents.  The first two are the GFS and ECMWF which are the two major worldwide weather models.  Nothing about these models is special to PredictWind, these are exactly the same two models that virtually EVERY weather forecast agency all over the world uses. ECMWF tends not to show in many "free" weather programs because you have to buy the results from the European Center for Mid-range Weather Forecasting.  The output from the GFS model is free to all from NOAA.

The other two models are the PWG and PWE are the PredictWind's "enhanced" versions of the output from the GFS and ECMWF models. I have not found them to be significantly more helpful than the actual model outputs.  I do not understand exactly what PW does to create this output from the major models.

In comparing model outputs to the & quot;real world" data, there are many things that can make them look different.  Starting with the fact that the most violent parts of a very large hurricane are actually a rather small weather feature on a global scale. 

PredictWind averages conditions over significant areas, and this can significantly impact the numbers.  In the highest resolution data available from PredictWind it still averages data over 50km.  That is a very large area when you are talking about a hurricane, where the highest winds are in a very narrow band around the eye.  To take this to an extreme example, PredictWind can not tell you about the wind speed in a tornado, it is too far small.  It's the same with a hurricane, although it obviously does better.

The GFS model itself only works internally to a resolution of 28km.  ECMWF model works at a higher resolution internally (9 or 10km, I think). So the models actually calculate a LOT more data than PredictWind presents, but they are still an approximation--at best--of what a real hurricane looks like.

Another issue is that it is not always clear about what wind number we are actually talking about.  Is the the 1 minute average?  the 3 minute average?  the surface wind?  The wind at 10 meter elevation?  All these numbers can be very different.  I don't know which of these numbers PredictWind presents.  I don't really care, for the way I use the program.  Many times the m edia presents the biggest number they can find because they sell more advertising that way.

I always caution people when they look at GRIB files created by computer programs. They look so PRECISE, it is so tempting to trust them.  They have none of the caveats that and weasel words that come from weather forecasters.  But these are NOT weather forecasts, and they are NOT reporting current conditions... they are the inputs that are used to create weather forecasts.  

Bill Kinney
SM160, Harmonie
Annapolis, MD, USA

---In amelyachtowners@..., wrote :

I bought Predict Wind a few months ago and  a Iridium G o to download offshore. I found it to under report winds with TS Gordon by a large margin,like 50%. Now with the Hurricane Florence and sustained winds of Cat4 140 mph reported for the last two days ,Predict Wind is showing from 68mph on PWG to 102 mph on GFS. Since this is a well reported storm I don't understand the under reported wind speed . Is PW generally this far off, can it be relied on? I asked PW about this and basically they said , that their models are"not geared to predicting hurricanes." I do not understand this explanation , a hurricane is simply a low pressure system, their models are not geared to predict low pressure systems ? I have been looking at their models and comparing them with known conditions. So far it is not reassuring , has it been found to be reliable ?
Thanks,
Pat
SM#123