Tropical Storm Leslie Encounters Dry Air, May Keep It Weak Enough To Miss First Trough

Lots of dry air lies in path of Leslie. Will keep it from intensifying in a big way, may also allow it to track further west (Courtesy of NOAA)

Tropical Storm Leslie is being closely watched by the US East Coast residents, especially after what we’ve seen with Hurricane Isaac. There remains a lot of uncertaintly with Leslie , same old story right? but as of now, I do believe there is probably no more than a 30% chance that Leslie will impact the US. That thinking is based on the fact we have a much stronger Azores high over the eastern Atlantic and a weaker Bermuda high with a trough over the western Atlantic. With already a northerly component to the track (WNW), this would suggest a recurve and threat to Bermuda and possibly the Canadian Maritimes.

Same old story, There’s lots of dry air ahead of Leslie

However, remember what I’ve been saying for some time now. The weaker a system is within the tropics, the further west it can go and with a lot of dry air in Leslie’s path, just like with Isaac, this may keep the system weak enough to not get grabbed by the trough to the NNW.

In fact, while the dry air keeps Leslie weak enough to continue riding the low level easterlies, pushing it further west.. once the first trough pushes east over the next 5 days, an area of weak steering winds develops into mid next week as a new trough re-establishes itself over the Central US and until it treks east, the steering flow over the western Atlantic will become nearly nonexistant and that may allow time for the atmosphere to pave out a new future track for Leslie.

All in all, a US landfall unfortunately cannot be ruled out and with a high concentration of dry air ahead of the system which can be clearly seen on the water vapor image at the top, a weaker system would certainly keep it tracking more west than north which would mean it misses the first trough and then a period of several days with little movement.

The secondary trough which develops over the US could be a problem for the East Coast as this may manage to pull Leslie WNW just as it begins to intensify perhaps to a Cat 1, 2 hurricane early next week. Models are pretty solid on this storm intensifying to potentially a Cat 3 but by then, is it too late to catch a steering flow out.

The latest GFS run pushes Leslie beyond 75W and then draws it due north, missing the New England coast by a smaller margin that you would feel comfortable with if you lived on Cape Cod, taking it into Nova Scota as a strong 955mb hurricane. Probably at Cat 2 intensity.

There is too many variables just now to determine a track but the dry air, like we saw with Isaac may be a problem once again for the US as this could keep Leslie, like Isaac weak enough for a further west track and a track which means the recurve is too late!

Here’s what the latest ECMWF and GFS charts show. Note the ECMWF keeps it well east of North America but GFS is much more threatening!

The GFS has a much stronger hurricane and takes it up into Nova Scotia but it’s not till Thursday Sept 13!



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