Tropical Depression Nine Forms in Gulf of Mexico

Tropical Depression Nine has formed in the Gulf of Mexico's Bay of Campeche, and will bring dangerous heavy rains of 5 - 10 inches to Mexico's Yucatan Peninsula the next two days. Satellite loops show that TD 9 has only a small amount of heavy thunderstorms near its center, and these thunderstorms are poorly organized, due to high wind shear of 20 - 30 knots. Mexican radar out of Sabancuy showed only one spiral band associated with the storm. Dry air from Mexico flowing eastwards over the western Gulf of Mexico is slowing development, but the topography of the mountains along the southern coast of the Bay of Campeche is helping to create counter-clockwise spin for TD 9, and likely aided in its formation despite the high wind shear. Sea Surface Temperatures (SSTs) are very warm, about 29.5°C. An Air Force hurricane hunter aircraft was investigating TD 9 on Wednesday morning, and found a well-defined surface circulation, top surface winds near 35 mph, and a central pressure of 1003 mb at 8:25 am EDT.


Figure 1. MODIS satellite image of TD 9 in the Gulf of Mexico on Wednesday afternoon, October 22, 2014.


Figure 2. Mexican radar out of Sabancuy showing one spiral band associated with TD 9 at 8:30 am EDT Wednesday October 22, 2014.

Forecast for TD 9
TD 9 is expected to move eastwards into Mexico's Yucatan Peninsula on Wednesday night, and likely has time to intensify into a 45 mph tropical storm, at the strongest, before making landfall. (The next name on the tropical storm list is Hanna.) The storm will spend most of Thursday with its center over land, and is small enough that passage over land may cause it to dissipate. Once TD 9 or its remnants are over the Western Caribbean on Friday and Saturday, it will interact with a trough of low pressure connected to the large Nor'easter affecting the Northeast U.S. The 8 am EDT Wednesday run of the SHIPS model predicts that while wind shear will fall to the moderate range, 10 - 20 knots, Thursday - Saturday, the trough will inject a large amount of dry air, discouraging development. The trough of low pressure will pull out of the Western Caribbean on Saturday, and may leave behind an area of spin in the Western Caribbean that would potentially have the capability to develop into a strong tropical storm or hurricane, as predicted by many of the ensemble members of the 00Z Wednesday morning run of the GFS model. The European and UKMET models are not showing this solution, but I think we have to be concerned about the possibility of a potentially dangerous tropical cyclone in the Western Caribbean early next week. It's a complicated meteorological situation, and the long-term forecast is murky.

Jeff Masters