2012 Atlantic Hurricane Season Birdseye Discussion #94A (Special Update)

By: NCHurricane2009 , 7:23 AM GMT on September 02, 2012

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...SEPTEMBER 2 2012...3:30 AM EDT...
Subtropical disturbance Invest 99-L forms well to the northeast of Tropical Storm Leslie in the open eastern Atlantic. While this may seem a feature that has popped up from nowhere...here are a few prior statements on this blog tracking the disturbance's origin:

Paragraph P4...mid-latitudes discussion...discussion #94...statement on cut-off upper vortex near the Azores and surface trough diving southward

Paragraph P4...mid-latitudes discussion...discussion #93...statement on cut-off upper vortex near the Azores and surface 1021 mb frontal low.

Paragraph P3...mid-latitudes discussion...discussion #92...statement on cut-off upper vortex forming near the Azores from Atlantic high seas upper trough...and statement on surface 1017 mb frontal low moving into the Azores.

Paragraph P2...mid-latitudes
discussion...discussion #91...statement on 1010 mb surface frontal low heading toward Azores suppored by Atlantic high seas upper trough.


Paragraph P2...mid-latitudes discussion...discussion #90...statement on 1018 mb surface frontal low in north-central Atlantic supported by NW Atlantic shortwave upper trough merging with parent high seas upper trough.

Paragraph P2...mid-latitudes discussion...discussion #89...statement on 1020 mb surface frontal low north of Bermuda supported by NW Atlantic shorwave upper trough

Paragraph P2...mid-latitudes discussion...discussion #88...statement on new 1019 mb surface frontal low north of Bermuda supported by NW Atlantic shortwave upper trough originating from parent upper trough moving into Atlantic high seas.

My most recent prognosis on this disturbance in paragraph P4 of discussion #94 was that the surface trough was dissipating...and the upper vortex was diving southward about the upper ridge cell inflated by Kirk and Leslie's outflow. Moreover...the upper vortex was merging with an inverted upper trough near the Cape Verde Islands mentioned in paragraph P6 of that discussion. As such...I had seen this disturbance as something insignificant...and planned in future discussions to move it into the tropical belt section as merely an upper vortex embedded in the upper ridge described in paragraph P6.

Now with this disturbance being upgraded to Invest 99-L and given a 20% chance of subtropical or tropical cyclone formation on the 2 AM EDT NHC outlook...I am re-assessing the situation. For my next full discussion...I am deciding whether to keep this upper vortex and surface trough in its own mid-latitudes paragraph...or better yet provide its own special feature section. Satellite imagery suggests the t-storms of the surface trough are aided by the intrinsic cold temps of the upper vortex. As the surface trough and upper vortex continue southward in tandem...the system is moving over increasingly warm waters that creates an increased surface to upper air temp contrast with respect to the upper vortex's cold air...hence increasing the system's instability necessary for subtropical or tropical cyclone formation. My action on this system in my next full discussion will be dependent on if the t-storm activity continues to improve on satellite displays.

Return to full discussion #94 for my latest assessment on the rest of the Atlantic tropics.

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