1 P4.6 DOCUMENTATION OF THE OVERLAND REINTENSIFICATION OF TROPICAL STORM ERIN OVER OKLAHOMA, AUGUST 18, 2007 John P. Monteverdi* San Francisco State University, San Francisco, CA Roger Edwards Storm Prediction Center, Norman, OK 1. INTRODUCTION During the evening hours of 18 August 2007 to the early morning hours of the 19 th , Tropical Depression Erin dramatically reintensified over Oklahoma, after having apparently dissipated (Fig. 1) over west Texas and eastern New Mexico. The remnants of Erin reintensified about 500 mi (~800 km) in linear distance from landfall, after traveling approximately 700 mi (~1100 km) on a curving overland path. Maximum sustained winds of nearly 90 km h -1 (with gusts to over 120 km h -1 ) were recorded by the Oklahoma mesonet (Fig. 2). In addition, 24 h rainfall totals 4 to 8 inches (102-203 mm) of rain were common over most of central Oklahoma (Fig. 3). The storm yielded a cluster of severe thunderstorm events, including tornado and convective wind gust reports (Fig. 4 and Table 1). During its transit across Oklahoma, Erin developed warm core characteristics, and showed a radar and satellite evolution consistent with that of nascent tropical cyclones. Nevertheless, this storm was never reclassified a tropical storm by the National Hurricane Center, chiefly because the reintensification did not take place over the ocean. Figure 1. Track of Erin’s center at 6 h intervals (black symbols) and forecast of 12 h positions after 12 UTC 18 August 2007 (Source: U.S. Navy). *Corresponding author address: Prof. John P. Monteverdi, Dept of Geosciences, San Francisco State University, 1600 Holloway Avenue, San Francisco CA 94132; e-mail: montever@sfsu.edu Previous studies (e.g., Bassill and Morgan 2006) have shown that when surface conditions over the continent are favorable, reformation of a tropical system can take place. However, documentation of such redevelopment has been sparse. This study documents this remarkable redevelopment of a tropical system over land. Figure 2. Oklahoma Mesonet meteograms from Watonga and Ft. Cobb, OK, showing sharp pressure fall and strong wind shift between 1000 and 1300 UTC (0300 to 0600 CDT) as eye of redeveloped Erin passed. Note wind gusts between 70 and 80 mph (31-36 m s -1 ) at both locations. Figure 3. Total rainfall (inches) observed by Oklahoma Mesonet, 0000 UTC 18 to 0000 UTC 19 August 2007.