FLHurricane.com: TD#7 Forecast Lounge

Some thoughts on 97L:
97L has found itself tucked up under some very impressive divergent flow aloft as the day has progressed. All quadrants showing anticyclonic motion, encouraging strong up-welling restoring force, lending to on-going eruption of intense convection all along a perceived trough axis that extends west to east from the Islands to ~ 300 nautical miles E. Given to the big oceanic heat content and that divergent field aloft, and considering the apparent absence of inhibitory dry air and/or SAL contamination ... TPC's electing to bump the hash region to solid medium seems almost an understatement. Currently 40% for the first 24 hours, and 50% over the next 5 days.

Having said that, the modeling et al has not been very committed to 97L. The CMC (Canadian global model) was (of course) the only g-based model that had been developing 97L. However, now the HWRF (tropical NAM/WRF model...) is also developing a small TC, taking it to between Fl and the lower Bahamas by 126 hours.

What I find intriguing is that the recent run of the experimental Roundy Probabilities product shows that right around day 5, there is a fairly large region of positive anomaly for development, situated right in that general area.

It should also be noted that the Madden-Julian Oscillation has been flagging this first two weeks of September as a more favorable arena compared to the suppressive nature of the overall circulation that had dominated much of the summer through August.

Should a TC evolve from 97L:

A shallower system may take a more westerly track through the Caribbean. One note about that; climatologically, systems tend to have a tough time getting their act together in the far eastern Caribbean sea. The reason for that has to do with systems tending to get entangled in the monsoonal exchange between NE South America and the adjacent region of the southwest Atlantic Basin. Downward vertical motion from land-based intense convection tends to compensate/mute the upward vertical motion associated/necessary with/for developing TCs. That can be overcome; the in situ circulation does not at this time appear to be taking on that longer term tendency, so we'll see...

Contrasting, a system that develops in earnest would likely tap the deeper layer steering field, and that would likely mean a more polar-ward position out in time.

John (Typhoon Tip)

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