Is the gap closing.....

[dixiebreeze]

Thanks for the explanation and graphics DS.

[WxGuy1]

No, I don't think the gap is closing. While the GFS is no longer forecasting a massive cut-off low meandering like it had been previously, it is still showing very strong southwesterly flow aloft downstream of the ridge axis across the western Atlantic. For example, LOOK HERE for the 250mb wind forecast for Wednesday. Yes, that's a large area of >100kt 250mb flow east of North Carolina, so any storm in that area will get sheared to bits given that low-level flow is much weaker. There is a very sizeable swath of southerly flow south of the main jet streak as well, so I find it very highly unlikely that Florence will not get kicked out to sea. The only real possibility of that not occurring, IMO, is if it stays south far enough to avoid the strongest southwesterly flow aloft. I think that would require Florence to move much slower than forecast (and much slower than is currently occurring).

At it's current pace, and with the NHC forecast, Florence will be entering the downstream portion of the trough by the time the trough really begins to intensify. In other words, Florence is forecast to move northward / be recurved by the upper-level trough (it's almost to the size of being a long-wave trough) before the trough is even near it's peak intensity. To lend support to the GFS, the ECMWF forecast shows a very similar solution, with the trough a little more continuous (upstream - downstream) and perhaps a little farther south.

Now, I do think Florence could become a gargantuan-sized cyclone as it begins to head NW and N (and eventually NE). It should be nicely positioned in the region of strong ageostrophic curvature divergence aloft near the inflection point of the trough to it' west and the ridge axis to its east. The models are picking up on this, showing a monstrous storm bythe middle of next week. Fortunately, this storm should be a very long ways east of the US coast, though it's western portions may glance coastal Maine as it accelerates rapidly north-northeastward and transitions to an extratropical cyclone.

The strength of the surface ridging (a very large 1024mb high) behind the upperlevel trough supports the intensity of this trough (e.g. temps in the low-mid 40s possible across most of the northeastern US by Wednesday morning (see HERE).

I always caution strongly against looking at forecast paths beyond 72 hours, but this storm's path will be dictated by very large, synoptic patterns for which models have a pretty good handle. Most of the time, the global models can forecast the synoptic, upper-level features pretty well out to 5-6 days. Yes, the specifics may not be there, but the general idea of a strong upper-level trough moving off the eastward seaboard, with a strong surface ridge nosing through the eastern US behind the trough axis seems plausible and is within the forecast capability (esp since there's decent agreement among different global models).

Now, after this trough pulls away, it looks like the east coast will be open fully for business. The GFS is showing a gigantic upper-level cutoff low parking itself over the western 1/2 of the country. Strong ridging aloft is progged to build back into the eastern US. I would be much more concerned about landfalling storms after the end of next week given this pattern. Of course, this is now 8+ days out, so a big grain of salt is necessary.

[gatorcane]

That is some trough let me tell you. Maybe the models are overexaggerating it?!??

[storms in NC]

JIMO here I think it will miss the trough . The trough is moving at a good rate of speed and TSF I think is to low for the turn out to sea so fast as the NHC has it. It will come close to the eastern seaboard and dump rain and big swells on the coast line. I don't think a hit will happen but as big as this is to be rain for the eastern seaboard.But I could eat crow too LOL