Reintensification of Tropical Storm Erin (2007) over Oklahoma

On 12 August 2007, a mesoscale region of low-level cyclonic vorticity organized along the western tip of Cuba in association with deep, moist convection (DMC). This antecedent mesoscale region of DMC and associated low-level cyclonic vorticity subsequently organized and intensified into Tropical Storm (TS) Erin over the Gulf of Mexico on 15 August. TS Erin made landfall along the Texas coast at 1200 UTC 16 August with attendant surface winds near 15–20 m s-1. Although weak at the time of landfall, TS Erin made an impact on the daily weather from Texas to the northern Great Plains, and to the eastern United States during the postlandfall period of 16–22 August. In particular, TS Erin was noteworthy for: (1) producing widespread rainfall > 150 mm over the Texas hill country during 17–18 August, (2) briefly reintensifying to TS strength over western and central Oklahoma on 19 August, (3) contributing deep tropical moisture (precipitable water values > 50 mm) to a widespread heavy rain event (local rainfall totals > 250 mm) over the southern Great Lakes region on 19 August, (4) producing heavy rainfall > 150 mm over Missouri on 19 August and Kentucky on 20–21 August, and (5) triggering a severe weather outbreak over North Carolina and Virginia on 21–22 August.

The purpose of this presentation is to examine the brief reintensification of TS Erin to TS strength during 0000–1200 UTC 19 August over western and central Oklahoma. The results suggest that reintensification occurred as intense DMC formed in conjunction with a weak surface boundary south and east of Erin's circulation center where low-level frontogenetical forcing was maximized along the western edge of a tropical moisture feed. The intense DMC became better organized as the environmental 850–200 hPa northwesterly wind shear increased to > 25 m s-1 after 0300 UTC east of TS Erin in conjunction with the passage of an upper-level trough over southern Kansas. Intense convective cores associated with this organized DMC were advected westward relative to Erin, and wrapped into the center of the low-level cyclonic circulation. Axisymmetrization of the intense convective cores, and attendant low-level cyclonic vorticity maxima, contributed to the development of an intense low-level warm core (below 500 hPa) vortex. This reintensification process resulted in widespread sustained surface winds > 15 m s-1, with gusts > 30 m s-1, over western and central Oklahoma during 0500–1000 UTC.