Hawaii's unemployment rate fell to a seasonally adjusted 4.3 percent in August, the lowest level in more than five years.  The State Department of Labor and Industrial relations reported today that the August rate was down from 4.5 percent in July. However, the department said data showed that along with the decline in unemployment the overall labor force shrank, suggesting some of those searching for a job simply quit looking. Hawaii's August unemployment rate compared with a 7.3 percent rate nationally.