Monday, August 26, 2013

Tropical Storm Fernand (2013)

Storm Active: August 25-26

On August 23, thunderstorm activity increased markedly in association with a tropical wave situated over the western Caribbean sea, just east of the Yucatan Peninsula. Over the next day, the system brought significant rainfall to the peninsula and to other parts of Central America as it moved west-northwestward. Late on August 24, a low pressure center was identified along the tropical wave, and despite still being over land, the disturbance became more organized.

The low emerged into the Bay of Campeche on August 25, allowing the warm ocean water to fuel the development of convection near the center of circulation. By the afternoon, the convection had developed prominent banding features, meriting the upgrade of the disturbance into Tropical Depression Six. As the cyclone formed, it was already in a stage of rapid development, and aircraft data indicated that Six had strengthened into Tropical Storm Fernand just two hours after its initial designation. In addition, however, the same data suggested that the center had reformed farther south, and the track adjustment reduced Fernand's time over open water. Therefore, even as a concentrated inner core of very cold cloud tops developed, bringing Fernand to its peak intensity of 50 mph winds and a pressure of 1001 mb, the tropical storm swiftly made landfall in Mexico very early on August 26. By late that afternoon, Fernand had dissipated.

In the above image, Tropical Storm Fernand was in the midst of rapid development, though this process was quelled almost immediately by interaction with land.

Fernand was a very short-lived system, persisting as a tropical cyclone for little over a day.

Thursday, August 15, 2013

Tropical Storm Erin (2013)

Storm Active: August 14-18

A strong tropical wave and associated low pressure system moved off of the African coast on August 13 and immediately began to organize. The next day, convection concentrated near the center as the system began to pass south of the Cape Verde Islands, bringing showers and some windy conditions. By the evening of August 14, the disturbance was sufficiently organized to be classified as Tropical Depression Five. At first, the highest winds were not situated over the center of circulation, but organization continued as the system tracked west-northwest, and by the morning of August 15, Five had strengthened into Tropical Storm Erin.

During that day, Erin was already struggling with the atmospheric dry air still present in that region of the Atlantic, fluctuating between periods of strong convection and nearly none at all. Meanwhile the cyclone turned slightly toward the northwest into a weakness in a ridge to its north, and entered a region of somewhat cooler waters. On August 16, wind shear out of the southwest increased also, driving convection off to the east of Erin's center, and the system was downgraded to a tropical depression. Late that night, however, a burst of convection reappeared, and satellite data suggested that Erin had restrengthened into a tropical storm.

Erin's new status was not to last, though, as the hostile conditions again tore away the cloud cover over the system's center of circulation on August 17. By that evening, the center also showed signs of elongation, and Erin was again downgraded to a tropical depression. The cyclone continued to degenerate on August 18, and became a remnant low that afternoon. The remnant low dissipated over the open Atlantic by August 20.

The image above shows Erin shortly after being named. The cyclone achieved only minimal tropical storm status.

A weakness in the subtropical ridge to its north allowed Erin to move northwestward into cooler water and very hostile atmospheric conditions. These conditions promptly dissipated the system.