| GFS: https://www.tropicaltidbits.com/analysis/models/?model=gfs®ion=atl&pkg=mslp_uv850 Euro: https://www.tropicaltidbits.com/analysis/models/?model=ecmwf®ion=atl&pkg=mslp_uv850 The 6Z, 12Z and 18Z runs today (Wednesday) of the main GFS have backed off on the kind of development it was showing. The 0Z run Wednesday had some development in the Gulf starting 8 or 9 days out with landfall around 10 days out. That showed Texas. Wednesday's 12Z Euro run showed what might be a weak tropical storm making landfall in SE Louisiana in around 9 days. I looked at several days of prior Euro runs that did't show anything. You can select which runs you want to view on the pages above in the drop down box that shows the time of the latest run. I would look at it like a possibility, but since the Euro has only had one recent run with it and the main GFS has backed off what it was showing, I wouldn't be too concerned at this point. If both starting showing something more consistently over several runs, or a day or two, then more of a possibility. The following is something extra about ensemble members that I would like to add though since it shows more chances of something possibly developing. In the blog entry I happened to post from Jeff Masters it mentions GFS ensemble members. I like to look at the Tropical Tidbits site for that too. The following links are for a specific run of the GFS, August 14th at 0Z. I want to show how ensemble members are nice to look at too. What it is showing isn't what I really want to point out, it's just an example using one run. Here is what that run of the GFS shows: https://www.tropicaltidbits.com/analysis/models/?model=gfs®ion=watl&pkg=mslp_uv850&runtime=2019081400 Now here are what the ensemble members of the GEFS show for that specific run: https://www.tropicaltidbits.com/analysis/models/?model=gfs-ens®ion=watl&pkg=lowlocs&runtime=2019081400 About the GEFS: https://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-ensemble-forecast-system-gefs "The Global Ensemble Forecast System (GEFS), previously known as the GFS Global ENSemble (GENS), is a weather forecast model made up of 21 separate forecasts, or ensemble members. The National Centers for Environmental Prediction (NCEP) started the GEFS to address the nature of uncertainty in weather observations, which is used to initialize weather forecast models. The proverbial butterfly flapping her wings can have a cascading effect leading to wind gusts thousands of miles away. This extreme example illustrates that tiny, unnoticeable differences between reality and what is actually measured can, over time, lead to noticeable differences between what a weather model forecast predicts and reality itself. The GEFS attempts to quantify the amount of uncertainty in a forecast by generating an ensemble of multiple forecasts, each minutely different, or perturbed, from the original observations." The GFS for that run shows perhaps a strong tropical storm making landfall in eastern Texas, around the TX/LA border. The ensemble members at the next link probably show either 20 or 21 ensemble members of the GEFS. (described above) There are 20 members, a control member and also in the ATCF system, where best track and model data is, an ensemble mean which might be an average of the 20 or 21) The red numbers at Tropical Tidbits are lows. And the numbers are the pressures. Something like 00 to 15 would be 1000 to 1015 millibars. You add a 10 before it. When the numbers start with something other than 0, 1 or 2, then you probably need to add a 9 before. So something like 95 would be 995 mb. 89 would be 989mb. Then to see an approximate intensity I like to look at the Dvoark chart: https://www.ssd.noaa.gov/PS/TROP/CI-chart.html I will note that I don't know if the pressure represented on that imagery are a good estimation of what the low of each ensemble member is. The resolution might not be too high so that it gets a good estimate of what the pressure might be. So they might read high. I don't know. The pressures shown on the main model imagery of the GFS seem pretty good on that site, but I don't about the ensemble imagery. That last line of the GEFS description above is why ensemble members are nice to look at. If a lot of them show the same thing, a low developing and a path to near the same place, then you have more confidence if that were to keep happening over several runs of the model that something might develop or something that is developed might take that path. I don't know exactly how it works, but small changes are made to each ensemble member in some manner. I don't know if these are some, but let's say shear is stronger in one or maybe the pressure is higher in one. If all the ensemble members still showed close to the same thing, then even if the model got something off at the start, there is still more confidence that something would move a certain way for example. Of course they aren't going to show the exact same thing, but that difference is what is important. I don't know if just the initial conditions are changed in each and/or the same changes are always made. I don't know enough about it. But when they differ greatly, it indicates that if something was off, perhaps just in the initial conditions of the model, the path could vary greatly. Or the strength could vary greatly. Maybe something doesn't even develop. Again, I don't know the changes that are made, but let's say one ensemble member had winds that were weaker and/or in a slightly different direction than another member. If both members still did about the same thing, that difference doesn't matter as much. But if they diverge greatly, then it matters greatly. Models aren't perfect. They aren't going to get the initial conditions exactly right. Something like weather balloons help in this. If a forecaster saw that the ensemble members are all over the place, then knowing what the conditions are and will be are very important because if something is slightly different that what they might expect, the path and/or intensity could vary, perhaps greatly. When the NHC for example looks at other models and a lot show the same thing, that gives them confidence that the storm might do that. When they are spread out, there is more uncertainty and the path and intensity are more uncertain. Again, I don't know a lot about ensemble members, that's just what I like to look at. So in looking at those two links I mentioned for that one run, you can see the spread in the ensemble members compared to the main GFS. As you go out in time the ensemble members are likely to get a lot more spread out. Other models have ensemble members too. The Euro members like that are not on that site. They do have the Euro ensemble, which is the EPS (Ensemble Prediction System), but not that imagery with separate ensemble members. The Canadian model does. That is GEPS (Global Ensemble Prediction System) on that site. About that one: https://en.wikipedia.org/wiki/Global_Environmental_Multiscale_Model#Ensemble_model And current link to the Canadian ensembles individual member pressures: https://www.tropicaltidbits.com/analysis/models/?model=gem-ens®ion=watl&pkg=lowlocs Canadian model isn't know for being as good for tropical cyclones though. Maybe they've made changes though. In Jeff Masters blog from Monday he said this: "About 20% of the members of the 0Z Monday GFS ensemble forecast were giving support to a tropical depression spinning up in the northeastern Gulf of Mexico early next week." I don't know what site he uses for imagery, but here is that GFS ensemble (GEFS) run at Tropical Tidbits: https://www.tropicaltidbits.com/analysis/models/?model=gfs-ens®ion=watl&pkg=lowlocs&runtime=2019081200&fh=204 I didn't quite see that much in the model imagery at Tropical Tidbits for that run. But I will point out the current runs of the GEFS: https://www.tropicaltidbits.com/analysis/models/?model=gfs-ens®ion=watl&pkg=lowlocs Do show a lot more lows in the Gulf starting in about a week. (not meaning more than one actual low, just many ensemble members showing a low of some sort) So while the main GFS doesn't show much, the GEFS is indicating more of a possibility of some kind of possible low developing. I'm not sure how reliable the pressure are, but most seem low. Most have a 0 as the first number. Again, 05 would be 1005mb. In the 18Z run on August 14th I see only one of the members with something stronger, as low as 82 on the image, which would be 982mb. When looking at ensemble members I wouldn't give weight to something like one. But I wanted to point it out just to kind of see how they work. So you can see that looking at just the main GFS doesn't tell the whole story, but until the GFS itself gets more onto something consistently, as well at the Euro, I wouldn't be too concerned, just aware that there is a possibility. |