Songda was an exceptionally powerful typhoon last week, when it menaced the Philippines, Taiwan and Okinawa.

At the height of its life cycle on May 26, Songda held super-typhoon status with top winds being 161 mph. This speed is within the fold of Category 5 Atlantic hurricanes.

NASA image of Typhoon Songda off northern Philippines, taken May 27, 2011.

The question thus arises: How abnormal is a super-typhoon during the month of May?

Only a small fraction the entire year’s western Pacific named storms ever gain super-typhoon status. The last storm to do so was Megi during October 2010. Megi was one of the most powerful tropical cyclones ever measured.

The last super-typhoon to form during a month of May actually happened recently. During May of 2008, Typhoon Rammasun had 155-mph highest 1-minute average sustained winds, according to the Joint Typhoon Warning Center (JTWC).

According to Wikipedia, the during the period from 1959-2005, an average of 31.6 named storms occurred yearly, of which 1.4 happened in the month of May.

The Japan Meteorological Administration (JMA) states that 25.6 named storms happened yearly during the period from 1951 through 2010. The month of May had an average of 1.1 storms.

Both references show that July through October have historically been top months for tropical cyclones, accounting for well over half of the annual tally, in the western Pacific basin.

JTWC defines “super-typhoon” as a typhoon having maximum sustained 1-minute surface winds of at least 130 knots, or 150 mph. This would thus be equivalent to a Category 5 or strong Category 4 major Atlantic hurricane.

As of Monday, May 30, Songda no longer existed as a named tropical cyclone. It has become an “extra-tropical”, or mid-latitude, storm sweeping eastward off the eastern coast of Japan.