Nea Post, the 15-year-old Huntington Beach amateur who plays piano at night after an afternoon of surfing, was in tune with the waves again Thursday. Just before the incoming tide began making the sea discordant, Post won her second-round trials heat to advance to today's main event against Australian pro Pam Burridge. . . . Jolene Smith, runner-up to Post Wednesday, also won her heat Thursday to advance to the main event, which happens to include her fourth-seeded twin sister, Jorja. . . . Tournament officials are still hoping that Hurricane Hillary, raging 461 nautical miles west-southwest of Cabo San Lucas near the tip of Baja, Calif., will increase the size of the waves in time for Saturday's finals. Most of the waves so far have been three- to four-footers with occasional peak sets reaching five and six feet. The National Weather Service in San Diego says Hillary, which is supposed to weaken Saturday morning, might have a slight effect on the surf of south-facing beaches. Huntington Beach faces west. However, the pull of the full moon will generate the highest tide of the year at 9:16 p.m. Saturday and could increase the size of waves. . . . Quarterfinals for seeded women and those who managed to rise through the trials, begin at 7 a.m. today. . . . Round two of the men's main event will begin about noon.