Tropical Storm Erin (2007) - Meteorological History

Meteorological History

On August 9, an area of convection developed just south of Jamaica in association with a trough of low pressure. The system tracked west-northwestward, and by August 10 consisted of a broad surface trough with minimal shower activity. Convection increased on August 11, and by August 12 the interaction between a tropical wave and an upper-level low in the area resulted in a large area of disorganized thunderstorms extending from the western Caribbean Sea into the central Bahamas. Upper-level winds gradually became more beneficial for development, and on August 13 a broad low pressure area formed about 90 miles (145 km) north-northeast of Cancún, Quintana Roo. Late on August 14, a Hurricane Hunters flight into the system reported a small circulation center, but at the time was not well-defined enough to result in the initiation of tropical cyclone advisories. However, deep convection was maintained near the increasingly organizing center, and at 0300 UTC on August 15 the National Hurricane Center classified it as Tropical Depression Five about 425 miles (685 km) southeast of Brownsville, Texas.

In the overnight hours after formation, the storm was disorganized with a ragged and ill-defined center of circulation. Located to the south of a mid to upper-level ridge over the southern United States, the system tracked to the west-northwest through an environment conducive for further strengthening; an upper-level anticyclone developed over the central Gulf of Mexico, and sea surface temperatures along its track were warm. The cloud pattern became better organized, maintaining a large area of convection with curved rainbands and well-established outflow. Based on reports from Hurricane Hunters, the National Hurricane Center upgraded the depression to Tropical Storm Erin at 1530 UTC on August 15 about 250 miles (400 km) east of Brownsville, Texas. As it continued northwestward, Erin remained disorganized and failed to strengthen beyond minimal tropical storm status. At 1200 UTC on August 16 the cyclone made landfall near Lamar, Texas as it weakened to tropical depression status. Three hours later, the National Hurricane Center ceased issuing advisories on Erin as warning responsibility was transferred to the Hydrometeorological Prediction Center.

Drifting northwestward through Texas, Tropical Depression Erin maintained an area of convection near the center, with its widespread but scattered rainbands dropping moderate to heavy precipitation. By August 17, the winds decreased to 20 mph (30 km/h), with higher gusts. The system turned to the north-northeast on August 18, while heavy bands of thunderstorms continued to rotate around the center of Erin. Early on August 19 after entering Oklahoma, the remnants of Erin suddenly re-intensified to maximum sustained winds of 60 mph (95 km/h) a short distance west of Oklahoma City. The Norman, Oklahoma National Weather Service remarked the intensification " in what amounts to an inland tropical storm;" at 0930 UTC the system presented an eye-like feature and a spiral rainband, and produced wind gusts of over 80 mph (130 km/h). However, a few hours later, the depression began weakening again, and late on August 19 Erin weakened significantly as the circulation dissipated over northeastern Oklahoma. Despite displaying tropical characteristics, the National Hurricane Center determined the system was not a tropical cyclone over Oklahoma, and classified it as a "low". The low continued into southeastern Kansas before dissipating, feeding moisture northward toward a frontal system extending from the Midwestern United States through the Mid-Atlantic States. Its remnant mid-level circulation then moved eastward across Missouri, Kentucky, and Virginia before losing identity as it moved out into the Atlantic Ocean.