ADULT ACHIEVEMENTS    Local adults traveled to compete in national events the last couple of months and collected some impressive results.    Bob Meyerdierks finished fourth in the men's 80-and-over USTA Clay Court Nationals in Virginia Beach and won the doubles with New York's Anthony Franco. James McKay teamed with Bonita Springs' Leonard Burge to place second. George McCabe was third in 75 singles and runnerup in doubles with Charles Nelson of Georgia.    Jeff Winkler reached the quarterfinal round in the 50 singles and doubles (with Richard Barrett of Alabama) in the USTA National Grass Court Championships in Philadelphia. Jeff Davis and Kevin Manning both played to the round of 16, as did Mark Wagner in the 45.    In the men's 65 USTA National Grass Court Championships in New Jersey, No. 5 Ralph Howe reached the round of 16 in singles and was second in doubles with  Robert McKenna of New York.    Marc Mazo finished to second in singles and doubles (with Jared Florian of Bradenton) in the USTA Men's 60 Grass Court National Championships in New York. Bill Christensen reached the round of 16 in the singles and Ralph Howe played to the quarterfinal round in the doubles with Pete Bostwick of New York. JUNIORS SHINE     Among the champions in last month's Seminole Super Series Challenge were area singles players Julia Sikorski in the girls 16, topseed Alexander Saltiel boys 16 and topseed Garrett Betsarakis 18 and doubles teams Emily Dvorak and Katherine Pyne of Bradenton in girls 18 and Adam Ambrozy and Christian Rincon of Lutz in boys 16.    Amy Lowther was runnerup in girls 16 singles, as was Agatha Ambrozy and Julia Sikorski in girls 18.    Kimberly Herrock won the girls 14 title in the Lake Cane Labor Day Super Series, and Aaron Carey teamed with Tampa's Vasil Kirkov to win the boys 12 doubles title.    Amy Lowther won the girls 16 title in the Super Series at the St. Petersburg Tennis Center. Finishing second were Garrett Betsarakis in the boys 18 and Miles Holvoet in the 16.    Fall Junior Rookie winners at East Lake Woodlands included girls 12 topseed Shannon Wagner, girls 14 Jordan Botsch, boys 16 Zachary Gardner and boys 14 Jacob Freifeld.    Capturing titles in the Clearwater Local Fall Championships were second seeds Jessica Stefan in the girls 12 and Natalie Boruk the 16, Anastasia Nefedova 18, topseed Dilan Scargle boys 10 and Juan Munoz 14. Runnersup included Laurel Wanger in girls 10, Ava Sowell 12, Cailynn Madsen 14, Coley Hungate boys 10 and Martyna Lukosiunas 14.