re: TS Jerry, TS Karen & More Areas to Watch - Peak Season

There hasn't been much to talk about the last few days as we wait for a complex wave breaking event that was set off by the tropical transition of Dorian. This same wave breaking event will get influenced by Gabrielle as it moves into the high latitudes.



Eventually a surge in the trades will allow future 95L to catch up with 94L but it's unclear what that interaction will look like. Also, the wave breaking event set off by Dorian will leave a PV streamer out in front of these two waves. PV streamers enhance shear and bring down drier air from the mid latitudes.



The 18z GFS develops future 95L to the point that it has sufficient convection to fracture and eventually displace the PV streamer.



This is important since a stronger more organized system will be able to influence the PV streamer and a weaker system could encounter shear from the PV, keeping it weaker longer. The sooner a system develops the better.

As these waves move west they will encounter an increasingly favorable large scale pattern as a KW pushes into the basin.



In the chart above, time moves towards the bottom while the waves move from west to east across the equator. The blue shading is an indication of rising air, more favorable for development. So as we move later in September the Atlantic background state becomes more favorable. KW events are often associated with a burst of tropical activity.

Why is this concerning? The Day 10 Euro EPS, below, shows a stout ridge over the Eastern US. The ensemble models do show some pretty good skill out beyond Day 5 with the 500mb pattern. Also, the recent North Atlantic wave breaking and the Pacific pattern also favor an Eastern US ridge.



Now the D10 Euro EPS tracks, there is a pretty clear bifurcation in the data. A system that develops sooner and is stronger feels the trough moving out into the Atlantic sooner. This sequence would probably send a system curving off to the east of the ridge (blue circle). A weaker slower developing system probably gets trapped underneath the ridge (red circle).



Still a long ways to go. Will a system develop? How far north will it be when it develops? Timing of troughs? Strength of ridge? Too many questions to answer at this time but the large scale pattern does seem to indicate that there could be trouble after mid-month.