November 1, 2020
Yesterday Invest 96L became TD 29 and then Tropical Storm Eta. This year now ties 2005 with the record for highest number of named storms in the Atlantic on record. You can see the official track for Eta below. Eta is no threat to the US, but we do need to watch the area where Eta makes landfall late this week for something new to develop.
Levi Cowan does an excellent job explaining the situation with Eta and what the models are showing. If you have 13 minutes I recommend you watch his video from last night here: https://www.youtube.com/watch?v=9tVcZGOkD70
If all you're concerned about is Eta you can forego reading the rest of this email. I spend the rest of it explaining what I was seeing yesterday, talking about the possibility for development late this week, and talking about models a bit.
Looking at this morning's model runs, it seems like the GFS really was the odd man out yesterday. The GFS now brings Eta into Central America on Monday and no longer shows it stalling and then coming north. What is interesting is that both the Euro and GFS ensembles as well as some of the spaghetti models still show tracks to the north as shown below.
Spaghetti:
Euro Ensembles:
GFS Ensembles:
So what are these tracks to the north? Some of them are forecasts for Eta, although likely erroneous, but most are showing something else. What Levi explained last night is that Eta is part of a larger broad circulation in the western Caribbean. These tracks back to the north are picking up on the idea that this broad circulation might spit out another storm and send it off to the north late this week. This new storm could be what is left over from Eta after landfall or something else, but either way there's a fairly strong hint that something may develop. Last night's run of the Euro shows this idea well. This was confusing me a bit yesterday and I thought it would be informative to show you a few models. The first animation below is the vorticity product at 850mb, which is the large scale spin in the atmosphere at about 5,000ft. It is my go-to product to look for tropical cyclone development. The large circular orange and red areas are storms. You can see Eta make landfall and then something else come north. Ensembles can be confusing to look at, after a time it is really hard to tell if you're tracking the same storm or something new. The second animation below is the "spaghettios" product from the Euro ensemble model, the EPS. It is showing the locations of low pressure systems from 51 different members. After showing Eta going ashore you can easily see how it quickly becomes difficult to track what is going on and it is impossible to tell if it brings what is left of Eta back north or something new. Either way it is still very informative and you can get an idea how well the operational Euro, the first animation, is doing if it is in fairly good agreement with the general trend you see in the ensembles. Ensembles also help you sniff out things that the operational models aren't showing. Many times this year both the GFS and Euro failed to show development but the majority of their ensembles did, especially with the GFS. This was telling us that we should not be trusting the operational models, especially when we had a robust tropical wave entering an area where conditions were ripe for development. Please, ignore anything out beyond 120 hours, models are fairly unreliable past 5 days for forecasting although you can use the longer term maps to get an idea of what may be possible.
Hopefully that long explanation was informative or at least interesting. I think we can feel good that Eta isn't going to come north in the short term but we need to watch and see what happens towards the end of the week regarding the possibility for new development.
Unless something changes significantly I'll probably wait until midweek to send out another update. Have a great Sunday.
Chris
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