Tropical weather analysis - August 12, 2011

By: KoritheMan , 6:01 AM GMT on August 12, 2011

Invest 92L

A tropical wave located between the Cape Verde Islands and the Lesser Antilles ("92L") has become less organized over the last 24 hours, and the prospects of it developing in the near-term appear to be diminishing. A low-level circulation is pretty much impossible to detect on shortwave infrared imagery, and convection near the suspected center (13.3N 35.1W as of 2:00 PM EDT Thursday) is nonexistent.

Figure 1. Latest infrared satellite image of Invest 92L, courtesy of NOAA's Satellite Services Division (SSD).

A secondary area of vorticity exists within the convective mass displaced to the northwest of the previous coordinates, but this is primarily mid-level. It appears that 92L's lack of organization can be attributed to dry air intrusion and moderate easterly shear, as derived from total precipitable water animations from CIMSS as well as satellite-derived high cloud motions.

The biggest hurdle to 92L organizing further is the dry air. Aside from that, conditions still appear conducive for development, and we will need to monitor this area in subsequent days as it gets farther west.

Interests in the Leeward Islands should monitor the progress of this system over the next several days.

It could still pose a long-range threat to the US east coast.

Invest 93L

A strong tropical wave located about 275 miles south-southwest of the southern Cape Verde Islands ("93L") continues to produce showers and thunderstorms. This activity currently remains within the confines of the western end of the wave axis due to easterly shear. Nevertheless, upper-level winds should begin improving over the next day or so, and remain within the favorable range throughout the forecast period (five days).

Figure 2. Latest infrared satellite image of Invest 93L, courtesy of RAMMB satellite division.

This system appears to be relatively insulated from the ambient subsidence that 92L is dealing with. This is not an uncommon occurrence in this part of the Atlantic during the Cape Verde season, where one wave paves the way for another.

Despite the tenacious nature of 93L, synoptic data suggests that this system lacks significant lower cyclonic turning. This, along with the easterly shear, should keep development gradual.

Having said all of that, I do anticipate that 93L will eventually become a tropical depression, likely on Sunday or Monday.

Interests in the Leeward Islands and Puerto Rico should monitor the progress of this system in subsequent days.

Like with 92L, this one could also pose a long-range threat to the US east coast, but it is far too early to speculate about either right now. Just sit back and relax. Things will change.

However, it is worth noting that the trough depicted in the models, while vigorous, is also short-lived. This is a similar situation we saw with Don, where he missed the trough due to it lifting out too quickly. Additionally, last year's flurry of recurves was triggered, at least partially, by large, powerful, and slow-moving Danielle. Such powerful hurricanes can act to reinforce a preexisting weakness within the ridge, thereby paving the way for recurvature of a subsequent storm following a similar trajectory.

Assuming 92L does not significantly develop in the coming days, or stays relatively weak, it might allow for 93L to come farther west since it will not be able to amplify the ridge much.

Again, we have plenty of time to watch this.


There are two additional disturbances at the present time. One is located in the central Atlantic about 800 miles northeast of the northern Leeward Islands, and the other is located about 250 miles west-northwest of Bermuda. Environmental conditions appear conducive for both of these systems to undergo additional development over the next few days.

The former may eventually pose a threat to land, given that it is forecast to move west-southwest by the NHC, but this is speculative at this juncture. The latter is no threat to land other than perhaps Atlantic Canada, and it should become absorbed by a frontal zone over the next day or two. Thus, if it is going to develop, it needs to hurry.

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3. scott39
6:48 AM GMT on August 12, 2011
Thank you! Always enjoy reading your synopsis.
Member Since: June 13, 2009 Posts: 0 Comments: 7253
1. MiamiHurricanes09
6:13 AM GMT on August 12, 2011
Thanks for the great update Kori. Always appreciated.
Member Since: September 2, 2009 Posts: 131 Comments: 21517

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