Threat for Home-grown Development in the Western Gulf next Week

   Posted by Levi at 5:08pm on August 16, 2012

The deep tropics are quiet today. Tropical Storm Gordon has formed way up in the northern Atlantic, and may threaten the Azores as likely a tropical storm in a few days, but could become a hurricane before that time. Overall, he is not a significant threat, but illustrates again how storms this year are waiting to develop and strengthen until they are well north of the tropics.

Of interest in the near-term are the remnants of tropical depression 7, which are currently over central America. Last week I flagged these remnants as a potential redevelopment issue in the western Gulf of Mexico due to the robust mid-level wave signature that has remained with the system despite the dissipation of the surface circulation. A weakness in the ridge over the western gulf due to a trough digging into the south-central U.S. over the next few days will be drawing TD7’s remnants northwestward along the coastline of the western gulf. This trough is forecasted to take its sweet time in leaving the scene, and will cause the pattern to remain rather stagnant for the next 6-8 days or so. An old frontal boundary will be dropping down over the northern gulf during this time in association with the upper trough, and could provide a focus of convergence to allow redevelopment of low pressure very near the Mexican coastline.

The evolution of a pattern where an upper trough is moving eastward to the northeast of a tropical disturbance can be favorable for development because of the high pressure that develops on the back (western) side of the upper trough, promoting surface convergence and piling up of air near the tropical disturbance. Dry air off the continent can initially be an issue for the disturbance in this situation, but as the upper trough gradually moves on, the surface high pressure also moves eastward, and eventually opens up a moist southeasterly flow into the disturbance, making dry air less of an issue and igniting significant convection due to the still existing low-level convergence. I illustrate in the video above how this happens on last night’s 0z ECMWF run.

Overall, development chances will largely be modulated by proximity to land, whether TD 7’s remnants bury themselves in Mexico or end up 50-100 miles off the coast. With this system having the opportunity to spend several days near the coast with 30C SSTs in the western gulf, tropical development could eventually occur. The models are only showing hints of development right now due to the uncertainty of land interaction, but they were showing nothing last week, and have slowly started coming around to the idea that this could potentially develop in our back yard next week. Regardless of development, this pattern favors a rain event coming to the northern Mexican and Texas coastlines, possibly Louisiana as well, as this tropical moisture surge interacts with the old frontal boundary that will be draping itself across the northern gulf.

We shall see what happens!

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