Tuesday, June 16, 2015

Tropical Storm Bill (2015)

Storm Active: June 15-20

On June 12, disorganized thunderstorms began to appear in the northwestern Caribbean and the neighboring areas of Belize and the Yucatan Peninsula. The trough of low pressure associated with the activity moved northwest over the Yucatan Peninsula the following day and deepened, producing a well-defined arc of convection extending into the Gulf of Mexico. By June 14, the disturbance was generating gale-force winds but had not yet acquired a well-defined circulation. Vigorous storm activity continued as the system moved into the Gulf. Atmospheric conditions improved in the vicinity of the disturbance on June 15 and it became more concentrated. Since tropical storm force winds were already occurring on the eastern side of the circulation, the system was designated Tropical Storm Bill late on June 15.

Through the morning of June 16, an area of high pressure over the southeastern United States steered Bill quickly towards the coast of Texas. The storm experienced slight strengthening, reaching its peak intensity of 60 mph winds and a central pressure of 997 mb before making landfall in the central Texas coast just before noon (local time). Bill weakened over land but maintained a well-defined circulation that was very prominent on radar imagery. The system turned northward that night and continued to bring flooding rains to Texas and Oklahoma as it moved inland and weakened to a tropical depression on June 17.

Tropical Depression Bill weakened only gradually over the next few days, maintaining its identity remarkably well even hundreds of miles inland. It turned slowly toward the east, moving through Oklahoma and Arkansas on June 18 and into Kentucky and Missouri the following day. 3 to 6 inches of rain were recorded along the first states in Bill's path and totals from 2 to 4 inches continued over a wide swath around the center over the east-central United States. On June 20, Bill finally became post-tropical and began to produce severe thunderstorm activity across the mid-Atlantic region as it interacted with a frontal boundary.

The above image shows Tropical Storm Bill just after landfall in Texas.

Despite spending less than two days over water as a tropical cyclone, Bill persisted far inland. This was in part due to the wet soil along its path (there had been a good deal of rain before Bill) that provided moisture to fuel the cyclone's circulation. This phenomenon is also known as the "brown ocean effect."