13B.4 The Life-Cycle of Tropical Storm Erin (2007): Genesis, Postlandfall Reintensification, and Widespread Heavy Rain

Thursday, 4 June 2009: 9:45 AM
Grand Ballroom West (DoubleTree Hotel & EMC - Downtown, Omaha)
Thomas J. Galarneau Jr., NCAR, Boulder, CO; and L. F. Bosart and R. S. Schumacher

Tropical Storm (TS) Erin originated from a mesoscale disturbance that formed along the western tip of Cuba on 12-13 August 2007. This incipient disturbance became organized in association with an outbreak of deep moist convection (DMC) within a westward-moving African easterly wave. Erin intensified to TS strength over the Gulf of Mexico on 15 August, and subsequently made landfall along the Texas coast at 1200 UTC 16 August with attendant surface winds near 15-20 m sƒ{1. Although weak at the time of landfall, TS Erin made an impact on the daily weather from Texas to the northern Great Plains - including an unprecedented inland reintensification to TS strength three days after landfall - and to the eastern United States during the postlandfall period of 16-22 August. The aim of this presentation will be to assess the relevant physical and dynamical mechanisms contributing to TS Erin's genesis over the Gulf of Mexico and subsequent inland reintensification over Oklahoma.

Overnight on 19 August 2007 the remnant of Erin reintensified as it moved northeastward across west-central Oklahoma, producing sustained TS force (> 17.5 m sƒ{1) surface winds and a swath of heavy rainfall (> 200 mm). Observations suggest that reintensification of the remnant Erin disturbance began as a band of DMC formed along the southern flank of Erin. This band of DMC, with embedded intense convective cores, originated along a weak surface wind shift boundary where low-level frontogenetical forcing near the western edge of a southerly feed of deep tropical moisture was present. As these intense convective cores, likely associated with small-scale cyclonic vorticity anomalies, moved westward relative to Erin and axisymmetrized around the main cyclonic circulation, Erin intensified to minimal TS strength and developed characteristics of a warm core tropical disturbance.

Along with reintensifying to TS strength over Oklahoma on 19 August, TS Erin was noteworthy for: (1) producing widespread rainfall > 150 mm over the Texas hill country during 17-18 August, (2) contributing deep tropical moisture (precipitable water values > 50 mm) to a predecessor rain event (local rainfall totals > 250 mm) over the southern Great Lakes region on 19 August, (3) producing heavy rainfall > 150 mm over Missouri on 19-20 August and Kentucky on 20-21 August, and (4) triggering a severe weather outbreak over North Carolina and Virginia on 21-22 August.

- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner