A typhoon appears to have had a sex change. After tropical depression Cass hit southeastern China last month, David was the next name on the alphabetical list for western North Pacific tropical cyclones. But instead Typhoon Oliwa has swirled into the region. An Observatory spokesman said Oliwa had formed east of the International Date Line and had kept the name assigned on the list for the central North Pacific basin. He said Oliwa had crossed the Date Line on September 4 and had been moving westward. 'It is expected to turn gradually to the northwest in the next few days, with Japan being the most likely landfall.' He said it was rare for a central Pacific cyclone to venture so deep into the western North Pacific basin. The last time was in 1986.