Update on End of October Eastern USA Storm Threat

Another day’s worth of model runs have trickled in regarding the East Coast Storm Threat to end October. So, what did our major models do?


As we jump forward to Saturday, there are already differences on the GFS between last night’s run and today’s run.

-First of all, today’s run, on the right, is a little stronger and farther southeast with TD 18.

-The lead shortwave in the central US is more progressive (as in faster and not as deep) on the 12z run than on the 0z run, due to another shortwave diving into the US on the 12z US that was not there on the 0z GFS.

As we head to Saturday evening, the differences persist. On the 12z GFS on the right, TD 18 is still a bit stronger. The 12z GFS is actually a bit more impressive with the ridging over Greenland/eastern Canada and father west with the North Atlantic Low than the 0z run, however the trough over the central US is rather flat on the 12z run, as the shortwave continues to dive into the western US and broaden out the trough.

As we head towards Sunday morning, today’s (12z) run of the GFS continues to be a bit stronger and a little farther SW with TD-18 (near Bermuda) than last night’s (0z) run of the GFS. However, the central US trough is flat and not negative tilted, again due to a shortwave digging over the Rocky Mountains. On the 12z GFS, the Gulf of Alaska low pressure is also a bit weather and a bit farther north.

And finally, the Sunday evening of the GFS image. In both model runs (last night on the left, today’s on the right), the tropical entity (TD 18) is near Bermuda and moving out to sea. The system remains stronger on the 12z GFS than the 0z GFS. On both images, the ocean low over the northern Atlantic is beginning to move east, however the 12z GFS was more aggressive in weakening the ocean low and dropping it southeast. In either case, the trough does not capture the tropical cyclone, and there is enough of an escape hatch over the northwest Atlantic for TD 18 to escape out to sea, on the GFS.

Overall thoughts on the GFS:

There were changes in many regards from last night’s GFS run to today’s run.

  1. Today’s run dropped a new shortwave into the western US on Saturday, which consequently flattened the troughing in the central US compared to the 0z. Today’s run also weakened the North Atlantic low a bit more than last night’s run. This eventually gave TD 18 a chance to escape.
  2. With regards to TD 18 itself, the 0z run was better synoptically for the system to be captured by the central US trough, however the system itself was weaker and a bit farther northeast on the model than the 12z run. The 12z run was a bit stronger and farther SW with TD 18 initially, but this time, the synoptics did not favor it being picked up by the central US trough.

Canadian Model

Last night’s Canadian model is on the left…today’s Canadian model is on the right…images are on a 12 hour interval from Saturday morning through Sunday evening. There are some interesting differences between the two runs of the model:

  1. Last night’s 0z run was very deep and sharp with the central US trough. Today’s 12z run was much broader with the trough, resulting in a later phase.
  2. Last night’s 0z run was much stronger with the NW Atlantic ridging. This resulted in a slightly farther southwest track of the tropical entity (TD 18) prior to phasing with the central US trough.
  3. Like the GFS, today’s 12z run of the Canadian model was notably weaker with the Gulf of Alaska low pressure, which resulted in less ridging in the western US and a broader trough in the central US.

Regardless, both runs of the model showed a very strong system making landfall over the Mid-Atlantic either Sunday or Monday. However, the Canadian kind of trended towards the GFS, with a broader central US trough, a weaker Gulf of Alaska Low, and a somewhat weaker block in the northern Atlantic. The model still produced an epic coastal storm, however.

European Model

When doing a similar comparison between last night’s 0z Euro run (left) and today’s 12z Euro run (right), let’s see what things can be noticed. It should be noted that Euro images are only available every 24 hours, so the comparison isn’t quite apples to apples, but it works well enough.

  1. The 12z and 0z Euro runs were very similar in how they handled the Greenland/eastern Canada ridging and the North Atlantic ocean low.
  2. Although the 12z Euro was more progressive and a bit flatter with the central US trough than the 0z run, the trough ran into the block and had no choice but to dig south and pick up the tropical entity, TD 18, and phase it into a monster storm for New England in 9 days.
  3. The 12z Euro is different than the 0z Euro with it’s handling of northern Pacific features. The 12z Euro initially weakens the northern Pacific blocking (which has been a trend 12z overall) quicker than the 0z Euro did, HOWEVER it develops a new +PNA low over the Aleutian Islands, which raises heights in the western US just soon enough to help amplify the central US trough and aid it in phasing with TD 18.

Overall thoughts on the model trends today:

  1. Today’s 12z runs, in general, did trend a little bit away from an extreme solution. Before you tell me that the European and Canadian models did have extreme solutions, they both trended flatter with the central US trough, broke down blocking the Pacific quicker, and the Canadian had a weaker North Atlantic Block today than last night.
  2. It should be noted that despite the above, both the Euro and Canadian models did still produce extremely strong east coast storms in a week or so.
  3. In general, the extreme coastal storm idea is not any more or less likely than yesterday. Small changes in the North Pacific, which is a very poorly sampled region of the world, had bigger changes downstream over the US.

It will still take a few days to conclusively say whether or not this big storm idea will come to fruition. It will still be at least Thursday when the energy that will carve out the central US trough is over the N. American sampling network, and not until Wednesday or so when we get a better idea on what blocking over the Northern Atlantic will do. The big storm solution still remains possible until some of these questions are answered, but it is still much too early to sound any kind of alarm, because things still can and will change.

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