Tropical Depression Thirteen Forms

The National Hurricane Center (NHC) has begun issuing advisories on Tropical Depression Thirteen. Satellite imagery, scatterometer data, and ship observations this afternoon indicated that the large low pressure system located southwest of the Cabo Verde Islands has maintained a well-defined circulation and has developed enough organization to be considered a tropical depression.

The initial intensity of the depression was set at 30 knots based on scatterometer wind data of near 30 knots. The central pressure is based on reports from a ship observation during its traversal through the center of the cyclone over the past 12 hours. This depression is a large tropical cyclone with a
wind field that is more than 400 nautical miles in diameter.

The initial motion estimate was an uncertain 280/10 kt, based primarily on satellite data. The depression was located along the southern edge of a large deep-layer ridge that is forecast to steer the cyclone westward for the next 24 hours or so. After that, the cyclone should follow a west-northwestward motion through 120 hours. The official NHC forecast track lies close to the consensus model TVCN through 96 hours, and then leans toward a blend of the ECMWF, UKMET, and CMC models since the GFS dissipates the cyclone by 120 hours, a scenario that seems premature given the current large size of the cyclone.

Vertical wind shear was forecast to remain low at less than 10 knots over the cyclone for the next 48 hours. This favors steady intensification. However, mid-level moisture is only expected to be marginal during this time with humidity values around 60 percent or less. The drier air along with the large size of the cyclone are expected to temper the development process, and this was reflected by the slower-than-average intensification rate.

All in all, while the storm may become the next named tropical system Lisa, it appears likely to remain well out in the open Atlantic.

-Brian-

Category: Tropical