Wind predictions

[jtsailjt]

Originally Posted by Paul L

As I've tried to explain to you, PW and Windy display the models. They aren't the model. They both update the models each time they are released. If you looked at Windy without making any selection of weather model it probably defaulted to ECWMF

Below is a screenshot of Windy. You can see the choice of 4 different models on the right, with GFS selected and displayed.

Below the models it indicates that the GFS was updated 29 minutes ago.

Paul, yes I realize that all the weather apps base their predictions on the same models and that’s why in my OP I said I didn’t want it to be about one app vs another. I’ve also cycled through that part of the Windy hamburger in your screenshot to try to find one of the models that said something close to what the published predictions were, but the biggest number I saw until just a few hours ago was in the high 70’s knots, very far from the 140 or 150mph all the major “civilian” news sources have been predicting for at least 4 or 5 days. Even when knots vs mph is taken into account, the disparity in what the 2 apps I happen to have on my phone vs what I’ve been hearing elsewhere has been much more than I’ve seen in the past on either of these apps. I kept expecting them to update their prediction but as late as this morning, I could see no mention of wind speeds over 100mph and I find that very disconcerting and wish I understood the reason why the models that all the wind apps use seemed to be so far off from what we’ve all known was coming for several days.

[Paul L]

Originally Posted by jtsailjt

Paul, yes I realize that all the weather apps base their predictions on the same models and that’s why in my OP I said I didn’t want it to be about one app vs another. I’ve also cycled through that part of the Windy hamburger in your screenshot to try to find one of the models that said something close to what the published predictions were, but the biggest number I saw until just a few hours ago was in the high 70’s knots, very far from the 140 or 150mph all the major “civilian” news sources have been predicting for at least 4 or 5 days. Even when knots vs mph is taken into account, the disparity in what the 2 apps I happen to have on my phone vs what I’ve been hearing elsewhere has been much more than I’ve seen in the past on either of these apps. I kept expecting them to update their prediction but as late as this morning, I could see no mention of wind speeds over 100mph and I find that very disconcerting and wish I understood the reason why the models that all the wind apps use seemed to be so far off from what we’ve all known was coming for several days.

The models are fed with actual weather measurements from over the region they are forecasting. So the zero hour model display is basically the actual recorded data, then going forward is the predictions.
A couple of reasons you maybe be seeing lower winds than those reported on the news:
1. Wind speed in knots vs mph
2. The display defaults to average speeds, not gusts. You can set Windy to display gusts and .
3. The models are an average over a fairly large area. GFS uses 22km squares (13.6 sq miles), the euro model use 9km (5.6 sq miles).

[jtsailjt]

Originally Posted by Paul L

The models are fed with actual weather measurements from over the region they are forecasting. So the zero hour model display is basically the actual recorded data, then going forward is the predictions.

A couple of reasons you maybe be seeing lower winds than those reported on the news:

1. Wind speed in knots vs mph

2. The display defaults to average speeds, not gusts. You can set Windy to display gusts and .

3. The models are an average over a fairly large area. GFS uses 22km squares (13.6 sq miles), the euro model use 9km (5.6 sq miles).

1. I’m familiar that and took it into account. Just a few days ago PredictWind had Ida hitting the coast and the little wind arrows were only showing 40 knots vs 140mph on the news. Then they started increasing their prediction somewhat but I didn’t see anything above 78knots on either app until landfall was imminent and even then, nothing like 140mph.
2. The news was reporting maximum sustained winds of 140mph, and some were saying 150mph with gusts to 160mph.
3. Possibly this is part of the answer to why I was seeing such a big difference. But using 13.6 sq miles means a square less than 4 miles on a side and it’s hard to comprehend that wind speeds could vary by that much over the open ocean and stay that way for several days. Again, we’re not talking gusts, but rather maximum sustained winds.

I was a military pilot and then commercial pilot for 35 years so am accustomed to receiving and digesting weather info from various sources, but have never seen such a large difference between what several reputable sources were predicting versus what the news stations were reporting and what actually occurred, and it wasn’t just a snapshot that was soon updated and instead it persisted over several days. The reason I want to get to the bottom of this is because up until now my experience has been that these apps were pretty accurate, within a few % and almost always within about 10 knots. But imagine if you were in the open ocean looking at the wind arrows on PredictWind showing a rotating storm headed towards you that showed 40 knot winds in your location 2 days in the future and this forecast persisted until just hours before you got blasted by 150mph winds. If I saw a 40 knot prediction I’d alter my course to try to get to an area of less wind and prepare my boat for a beating and would assume I might see higher gusts, but wouldn’t be terribly concerned. But 150mph!!![emoji15]

[Paul L]

Jt,
Here's the hourly winds , with a few missing, from New Orleans airport.
https://w1.weather.gov/data/obhistory/KMSY.html

I don't see anything that implies 150 mph sustained.

[jtsailjt]

Originally Posted by Paul L

Jt,
Here's the hourly winds , with a few missing, from New Orleans airport.
https://w1.weather.gov/data/obhistory/KMSY.html

I don't see anything that implies 150 mph sustained.

It would have been quite a coincidence for the highest winds to have been right at the airport and I don’t think that happened either, but supposedly when/where it came ashore that’s how high they were, thus a Category 4, almost 5 hurricane.

[jimbunyard]

If I remember correctly, this 'discrepancy' has been previously discussed several times on this forum.

Suffice it to say that it is not really a 'problem' with the models utilized by the various 'reporting agencies' but with the 'model' that we all form in our heads to make sense of them.

For instance, we (Slidell) were recently hit by two pretty intense storms, Zeta last year and now Ida this one.

Zeta was much stronger here, but was moving so fast the damage had no time to accumulate.

Ida, on the other hand, was perhaps 20-30% 'less intense' (here), but those less intense conditions lasted literally about 20 times longer.

Compounded by the predictory models and their analysts failing to 'pick-up' on the effects of the massive amounts of hot water injected directly into the eye by its close passage to Lake Pontchartrain. Or their failing until it was too late to comment on them.

Ida's hugely expanded windfield 6-8 hours post-landfall certainly took many people's, including my, model by surprise.

Luckily, for me at least, my 'I could be wrong' model (mostly) overruled my 'nothing to worry about' model and I was for the most part prepared anyway.


I suppose I rely about equally on the 'electronic gizmos' available today and my goin-on-50-years hands-on forecasting ability using actual physical information to form my personal predictive model.

As for the purported 3-fold difference in modeled and observed numbers, I've never seen that, though I have seen almost a 2-fold difference, which I chalked up to the reasons amply discussed above and in other threads.

I fail to see what the difference in a spot reading of 100k vs 150k would actually make anyway; in any except pretty rare circumstances, either would denote a developed circulatory system a modern mariner would (should?) be aware of long before they encountered it's worst effects.

Modern electronic 'miracles' to the contrary.

[Yellowtulip]

Originally Posted by jtsailjt

Paul, yes I realize that all the weather apps base their predictions on the same models and that’s why in my OP I said I didn’t want it to be about one app vs another. I’ve also cycled through that part of the Windy hamburger in your screenshot to try to find one of the models that said something close to what the published predictions were, but the biggest number I saw until just a few hours ago was in the high 70’s knots, very far from the 140 or 150mph all the major “civilian” news sources have been predicting for at least 4 or 5 days. Even when knots vs mph is taken into account, the disparity in what the 2 apps I happen to have on my phone vs what I’ve been hearing elsewhere has been much more than I’ve seen in the past on either of these apps. I kept expecting them to update their prediction but as late as this morning, I could see no mention of wind speeds over 100mph and I find that very disconcerting and wish I understood the reason why the models that all the wind apps use seemed to be so far off from what we’ve all known was coming for several days.

The GRIB file readers make forecasts based on statistics gathered automatically. They do not display real-time data. The forecasts on mainstream media are usually made by meteorologists (ie, people) using not only statistical data but years of training and experience in interpreting the data.
GRIB files don’t give any indication of weather fronts either. They have to be inferred from the data, though as someone else pointed out, synoptic charts are much better for that purpose.

[Paul L]

Originally Posted by Yellowtulip

The GRIB file readers make forecasts based on statistics gathered automatically. They do not display real-time data. The forecasts on mainstream media are usually made by meteorologists (ie, people) using not only statistical data but years of training and experience in interpreting the data.
GRIB files don’t give any indication of weather fronts either. They have to be inferred from the data, though as someone else pointed out, synoptic charts are much better for that purpose.

Fronts can be inferred from the model displays pretty easily. Sure they aren't labeled like a synoptic chart, but any cruiser using GRIBs for route planning can see them. Here's a chart from today with a pretty obvious front.

[Yellowtulip]

Originally Posted by Paul L

Fronts can be inferred from the model displays pretty easily. Sure they aren't labeled like a synoptic chart, but any cruiser using GRIBs for route planning can see them. Here's a chart from today with a pretty obvious front.

As you say, that’s a pretty obvious one. They aren’t always so obvious. As I said they can be inferred, but it’s much easier and quicker on a synoptic chart.

[Paul L]

Originally Posted by Yellowtulip

As you say, that’s a pretty obvious one. They aren’t always so obvious. As I said they can be inferred, but it’s much easier and quicker on a synoptic chart.

If I could download 10 days of synoptic charts in an easy, compact format like GRIBs, then I would. Since its not an option, I'll stick with the GRIBs.

[LittleWing77]

Originally Posted by Paul L

Fronts can be inferred from the model displays pretty easily. Sure they aren't labeled like a synoptic chart, but any cruiser using GRIBs for route planning can see them. Here's a chart from today with a pretty obvious front.

Yeah, but it's the baro pressure readings and contour lines that are key...!

[jtsailjt]

Originally Posted by jimbunyard

If I remember correctly, this 'discrepancy' has been previously discussed several times on this forum.

Suffice it to say that it is not really a 'problem' with the models utilized by the various 'reporting agencies' but with the 'model' that we all form in our heads to make sense of them.

For instance, we (Slidell) were recently hit by two pretty intense storms, Zeta last year and now Ida this one.

Zeta was much stronger here, but was moving so fast the damage had no time to accumulate.

Ida, on the other hand, was perhaps 20-30% 'less intense' (here), but those less intense conditions lasted literally about 20 times longer.
.

I agree that there are other conditions other than just wind speed that determines what effect a hurricane will have on an area. But that’s a whole other subject from comparing predicted vs actual wind speed.

I really think it is a problem with the models they are using or the way they display them, at least in this one case, where less than a day before landfall PredictWinds wind arrows were only predicting 40 knots at the time of landfall and Windy was better but nothing even close to 150mph. That discrepancy isn’t in anyone’s head. It was what their apps said.

I’m doing a delivery this fall on a friends boat and he uses PredictWind via his IridiumGo and if I see a storm with 40 knot wind arrows in our path I’m hoping we can rule out it actually being a Cat 4 hurricane! I checked both apps multiple times leading up to the time of landfall and the predictions didn’t change substantially until just before landfall and even then they didn’t get much above 100kts.

[Paul L]

Originally Posted by LittleWing77

Yeah, but it's the baro pressure readings and contour lines that are key...!

And they are clearly visible on the GRIB display. See the example I posted above.

[Paul L]

Originally Posted by jtsailjt

I agree that there are other conditions other than just wind speed that determines what effect a hurricane will have on an area. But that’s a whole other subject from comparing predicted vs actual wind speed.

I really think it is a problem with the models they are using or the way they display them, at least in this one case, where less than a day before landfall PredictWinds wind arrows were only predicting 40 knots at the time of landfall and Windy was better but nothing even close to 150mph. That discrepancy isn’t in anyone’s head. It was what their apps said.

I’m doing a delivery this fall on a friends boat and he uses PredictWind via his IridiumGo and if I see a storm with 40 knot wind arrows in our path I’m hoping we can rule out it actually being a Cat 4 hurricane! I checked both apps multiple times leading up to the time of landfall and the predictions didn’t change substantially until just before landfall and even then they didn’t get much above 100kts.

Post #9 in this thread shows an estimate of 97kts prior to landfall using the ECMWF model displayed by Windy.

The NHC did say that there were sustained 150mph (130 kts), but from their warning it sounds like it was for a brief time in a very limited area. See this NHC note:
https://www.nhc.noaa.gov/archive/202...8291653.shtml?

As far as practical passage weather interpretation, if you see a closed low ( a low over a small area that is starting to circulate) predicted in the tropics, even outside of storm season, you need to be in heavy monitoring mode. If the closed low has 40kt wind predictions 3 or 4 days out then you pretty much have to either not believe the model or take serious precautions.
In this case you will often see the low in one model and it will not appear in another model. As the time gets closer the models tend to converge - perhaps to both show the deep low or perhaps for the low to disappear. It's all part of offshore passage weather.

[MicHughV]

be sure you are comparing the same units.....mph is typically 10-15 higher than knots....