Thursday, August 2, 2012

Hurricane Ernesto (2012)

Storm Active: August 1-10

On July 29, a weak low pressure center was identified southwest of the Cape Verde Islands. Some isolated showers and thunderstorms were associated with the system, and it was monitored for development. The system began to organize over the following days, though its circulation was inhibited somewhat by its proximity to the equator. The wave remained embedded in the ITCZ until July 31. However, on that date, the center shifted northward, allowing the low to organize further.

On August 1, there was enough convection accompanying the center to declare the system Tropical Depression Five. El NinĂ³-related shear from the northwest affected the system immediately, pushing dry air into the northern portion of the system. Meanwhile, strong steering currents were pushing Five westward at a fast clip, causing it to approach the Windward Islands on August 2. The circulation became more organized that day, and the confirmation of tropical storm force winds east of the center of circulation by aircraft reconnaissance resulted in the tropical depression being upgraded to Tropical Storm Ernesto.

Ernesto's initial winds were 50 mph, but its convection diminished overnight, causing it to weaken slightly as it crossed the Windward Islands early on August 3. The center reformed farther to the south later that morning, and the system began to reorganize as it entered the Caribbean. Ernesto's intensity fluctuated under marginally favorable ambient conditions, but the outflow and satellite presentation consistently improved overnight and into August 4.

As the storm moved through the central Caribbean that day, it decelerated slightly, though still bearing mostly west. Its outer bands skirted Puerto Rico and the southern Dominican Republic that evening. Over the next day, Ernesto lost some organization, its center became less well-defined, possibly due to dry air invading the cyclone. Ernesto's rapid motion also contributed to its disorganization.

On August 5, the weakened Ernesto lost any vestige of organized central convection, but still maintained low-end tropical storm intensity. It changed direction, now heading due west towards Central America.

That night, however, Ernesto continued its erratic behavior, and rapidly organized. Bursts of convection soon covered the center, and the cyclone's forward motion showed. During the morning of August 6, Ernesto quickly strengthened, and the beginnings of an eye became apparent on satellite imagery. Additionally, the system took a turn to the west-northwest.

That night, Ernesto's outer bands swept over Honduras, causing locally heavy rainfall and tropical storm force wind gusts. Dry air was evident in the interior of the northwest quadrant overnight, but the system's outflow continued to improved and the central pressure decreased into August 7.

By later that day, Ernesto finally became sufficiently organized to be upgraded to a hurricane. It continued to strengthen until that evening, reaching its peak intensity of 85 mph winds and a pressure of 980 mb just as it made landfall in the Yucatan Peninsula just north of the Mexico-Belize border at about 11:15 p.m. EDT, or 10:15 local time.

Over land, Ernesto caused localized flash flooding and heavy winds throughout the Yucatan and the neighboring parts of Central America. The system was downgraded to a tropical storm early on August 8, and continued to weaken through the morning, as it moved west toward the Bay of Campeche.

Late in the afternoon, Ernesto's center emerged over water, and the cyclone immediately began to restrengthen, despite its proximity to the Mexican coast. Its organized circulation allowed moisture to be drawn into the center, and the winds increased rapidly, bringing the system to near hurricane strength early on August 9, as torrential downpours continued over land. Under the influence of a ridge to its north, Ernesto turned west-southwest and made its final landfall in Mexico around noontime that day.

The cyclone maintained its structural integrity quite well over land, and so caused rain and tropical storm force winds through the remainder of the day and into early August 10. It was downgraded to a depression and dissipated later that morning. The remnants of Ernesto moved into the Eastern Pacific basin soon after, where they contributed to the development of Tropical Storm Hector.

Ernesto as a hurricane before landfall in Mexico.

Track of Ernesto.

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