Friday, September 7, 2018

Hurricane Isaac (2018)

Storm Active: September 7-15

At the beginning of September, a tropical wave moved into the Atlantic. Though it was producing some showers and thunderstorms, but the disturbance remained disorganized for several days as it traveled westward. By September 5, the low had become better defined, but convection was quite limited near the center of circulation. On September 7, the disturbance was classified Tropical Depression Nine. That day, it also became nearly stationary as steering currents collapsed and it felt the pull of newly formed Tropical Depression Eight (which would become Helene) to its east. The center was nearly exposed at first due to shear, but the system's organization increased considerably on September 8. This prompted an upgrade to Tropical Storm Isaac.

The storm was very small, with tropical storm force winds extending only a few dozen miles from the center. Such storms are subject to rapid changes in intensity, and Isaac did gain strength quickly over the next day. Meanwhile, it finally picked up some forward speed toward the west. During the evening of September 9, it was upgraded to a hurricane. There was little change to the system over the next day, despite generally quite favorable conditions. The banding structure and core of Isaac struggled to improve, even with low wind shear. Soon, the satellite presentation became more ragged in appearance and the system was downgraded back to a tropical storm.

Early on September 12, an upper-level trough north of Isaac caused a sudden increase in shear on the system, quickly stripping convection away from the center. The cyclone began to rapidly weaken as a result. Nevertheless, it caused scattered heavy rains and tropical storm force winds as it passed among the Leeward Islands and entered the Caribbean during the morning of September 13. Thunderstorm activity started to make a comeback near the circulation center later that day, but the circulation itself was ill-defined and showed signs of becoming elongated. Isaac weakened to a tropical depression on September 14. Soon after, all traces of a closed circulation vanished and the storm dissipated. The remnants of Isaac brought scattered thunderstorms to Jamaica a few days later.

This image shows the small Tropical Storm Isaac moving over the open Atlantic.

Isaac dissipated shortly after entering the eastern Caribbean. This is a quite common event and this region is often referred to as a "tropical cyclone graveyard" by meteorologists.

No comments: