typhoon_tip
(Meteorologist)
Mon Aug 23 2010 03:14 AM
Re: Tropical Depression Six Upgraded to Tropical Storm Danielle

Danielle has strengthened to a 50mph tropical storm this evening.

I have noticed that the deep convective cloud pattern has taken on much more cyclonic banding more centroid to the apparent CDO or CDO-like feature that rather abruptly exploded 3 hours ago. It is not uncommon for early developing TCs to have center jumps toward regions where UVM is persisting (the reasons can get complicated).

In any case, what appeared to be a deep plume of convection perhaps displaced slightly W of the llv circulation axis earlier this evening has become more collocated with the on-going rigorous and persistent CDO of CDO-like feature.

Also, the TC is moving more W by WNW and this forward motion is a negative vector against the incursion of ENE shear, such that storm relative shear has dropped off. That is similar to sticking your hand out a window while driving at 10 mph, with a wind at your tale of 20mph - you only experience a wind differential of 10mph. The same arithmetic applies in the atmosphere, such that a TC moving W at 10 mph with easterly shear of 20mph, only experiences 10 mph of bulk shear; which is not sufficient enough in most cases to prevent strengthening.

Any deep layer convection in that vicinity would be compelled to move more W given the surrounding environmental flow. When the convection erupted closer to the center of circulation earlier this evening, the center was pulled W and is now being guided again by a better coupled lower and middle atmospheric dynamic, both of which are then guided by the mid-level steering.

John



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