Monday, July 17, 2017

Tropical Storm Don (2017)

Storm Active: July 17-18

A mid-July tropical wave crossed westward from the coast of Africa to more than half-way across the tropical Atlantic without generating much thunderstorm activity. However, on July 16, the system began to organize, despite the proximity of dry air. A low pressure center formed shortly afterward, even as convection remained quite limited. During the afternoon of July 17, a curved band developed about the center and the circulation became better-defined. As a result, the low was upgraded to Tropical Storm Don about 500 miles east of the Windward Islands.

Over the next day, Don moved quickly toward the west. It strengthened briefly as a central dense overcast appeared, but increasing shear reversed this slight intensification as quickly as it had occurred. By midday on July 18, Don's disorganized thunderstorm activity was moving over the Windward Islands. That evening, before the system passed over the islands, Don lost its circulation center in the face of strong shear and dissipated. Scattered gale force winds and heavy rain did continue, however, as its remnants entered the Caribbean.

Tropical Storm Don was only a small cyclone for its brief existence, forming as it did on the edge of a dry air mass with limited moisture supply.

Don existed for less than two days before succumbing to high wind shear as it entered the Caribbean Sea.

Thursday, July 6, 2017

Tropical Depression Four (2017)

Storm Active: July 5-7

At the beginning of July, a tropical wave located southwest of the Cape Verde Islands began to organize. The system was moving rather slowly for its latitude over the next several days, allowing it to began circulating more easily than it otherwise would. Slowing development, however, was its interaction with the intertropical convergence zone (ITCZ). Even though this interaction generated a great deal of convection, the disturbance needed to separate from the ITCZ to initiate development. On July 4, the system began to veer toward the west-northwest and gain some latitude. The next day, it acquired a circular area of strong thunderstorms near its center and became Tropical Depression Four over the open tropical Atlantic.

Shortly afterward, however, the system began to feel the effects of a Saharan dry air encroaching from the north and east. On July 6, the depression continued to the west-northwest, but its thunderstorm activity slowly declined as it entrained dry air. In addition, the cyclone increased in forward speed, making it difficult for the circulation to persist. It did not persist long, in fact: the system lost a closed circulation and dissipated during the afternoon of July 7, far from any land.

The above image shows Tropical Depression Four over the open Atlantic.

The short-lived tropical depression fell victim to a large dry air mass quickly after formation.