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August 2012

TD 7 not a Significant Threat for Now; Atlantic Becoming Active

   Posted by Levi at 2:12pm on August 10, 2012

TD 7 has formed out in the central Atlantic, a bit farther north than Ernesto, but will be similar to Ernesto in many ways. Right now thunderstorm activity is limited to mostly SW of the center, and the center itself is mostly exposed. Dry air is impinging upon the system from the north, and the circulation is a bit elongated SW to NE. TD 7 is also embedded in a large-scale inverted-V wave signature, which is partially responsible for the elongation, and is resulting in a less robust circulation than what Ernesto had at this longitude. The short-term track will follow in Ernesto’s footsteps into the Caribbean, possibly a bit farther north, and the system will likely struggle for the next several days with dry air, wind shear, and fast trade winds making it difficult to maintain a closed circulation. Such conditions are prevalent often in the central Atlantic and central-eastern Caribbean during El Nino years such as this one.

I’ve decided to experiment with drawing my own forecast tracks to make my ideas more coherent. Below is my first attempt. My track closely follows the current NHC track on the southern side of the model guidance envelope, based on the previous poleward bias that the models had with Ernesto, and tend to have with weak central Atlantic systems in general. This track is also based on the premise that TD 7 will remain weak and get whisked along quickly westward by the trade winds, with little opportunity to strengthen and move poleward. While TD 7 may get named Gordon before reaching the Caribbean, strengthening of any kind will be hard to come by, and TD 7 could dissipate in the central Caribbean.

In the long-range, TD 7’s remnants may retain a mid-level signature and move towards central America and the western Gulf of Mexico into a potential opening in the ridge to the north. The CMC and GFS ensembles show TD 7’s mid-level wave structure taking this path in 7-10 days. Given the pattern this year favoring development farther west and north, it is possible that a former TD 7 getting into this region could pose a development threat down the road, though it is too far away to know at this time. In general, a southeasterly 500mb flow out of the Caribbean towards Texas indicates that tropical moisture will be advecting northward, and could be something to watch in the long range.

Elsewhere, a vigorous tropical wave has moved off of Africa and is moving across the Cape Verde islands bringing rare tropical rains to that area. Due to its northerly latitude, recurvature in to the middle of the Atlantic seems to be the likely future for this system, with no threat to land. Also due to its latitude, dry air is quickly choking the circulation, and development, if any, will be slow to occur, and the system will have to get significantly farther west and north if it is to have a chance at development.

We shall see what happens!