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August 2012

94L to Gradually Develop, Lesser Antilles Threatened First

   Posted by Levi at 3:10pm on August 19, 2012

Hurricane Gordon continues to move northeastward and will scrape the southern Azores as it weakens below hurricane status during the next few days.

The remnants of Helene officially dissipated well inland over Mexico as per the NHC yesterday. However, this morning we see the remnant rotation in the low-mid levels directly above Tampico, Mexico, right on the coastline of the western gulf. This small disturbance still poses a threat to try to redevelop over the water as it gets drawn north by an upper-level trough, represented by a frontal boundary that is pushing towards the northern gulf waters. Model support for redevelopment has waned since yesterday, but Texas and North Mexico should not ignore Helene’s remnants yet. Even if redevelopment does occur, the only change in the weather for the TX/MX coastlines will be slightly heavier rainfall than they are already getting. Louisiana will also be getting in on pulses of tropical rain over the next few days.

The big story continues to be Invest 94L in the eastern Atlantic. The system’s organization has changed little since yesterday, and as expected it should take its time in developing during the next few days. Dry air to the north is getting entrained and is hampering the development of deep convection, and the main center is competing with a rather large envelope of low pressure to the south and southwest within the ITCZ/monsoon trough. The global models, specifically the GFS and ECMWF, are starting to pick up on the slower rate of development of 94L due to the time needed to consolidate a circulation within such a large area of low pressure, and both of these models have actually ceased to show significant strengthening of 94L before reaching the Antilles islands, at which point it becomes entangled with Hispaniola and Cuba on both models and never strengthens again. These jumpy changes in intensity forecasts are typical of models when they are struggling with resolving the development of a tropical system within a large area of low pressure, and until solid development occurs, I think they will continue to struggle a bit with how to handle 94L. My intensity forecast is unchanged from yesterday, and I think 94L should get named Isaac before reaching the northern Antilles Islands in about 4 days. Folks there and in Puerto Rico should expect a strengthening tropical storm on their doorstep as a good possibility by that time. Thereafter, land interaction will largely determine the intensity, and the track is not nailed down well enough yet to know exactly how that will unfold.

The track forecast continues to look threatening for not only the northeastern Caribbean Islands but also the eastern United States. The pattern itself over North America and the north Atlantic is a classic for an east coast hurricane threat. The question is just whether a storm will be in the correct position to take advantage of it. 94L may very well be, as long as it doesn’t bomb out into a hurricane quickly, in which case it would recurve out to sea, likely between the eastern seaboard and Bermuda. The slow development of the storm now is bad news for the U.S. later, as slower development means a farther west and south track. While the global model solutions are currently erratic, due to their recognition of the struggles that 94L will face during its development, my long-range track has been nudged slightly to the southwest, but the forecast is largely an update of yesterday’s.

We shall see what happens!