Radius of outermost closed isobar

The radius of outermost closed isobar (ROCI) is one of the quantities used to determine the size of a tropical cyclone.

It is determined by measuring the radii from the center of the storm to its outermost closed isobar in four quadrants, which is then averaged to come up with a scalar value.

[3] Previously, a database was created to determine ROCI values for the western north Pacific Ocean in 1972, using data from 1945 to 1968.

[4] Another database with additional ROCI information is currently being modified at the Hydrometeorological Prediction Center for use in matching ongoing tropical cyclones to past systems for the purposes of finding rainfall analogs to an ongoing event,[5] which has fairly continuous data running back to 1959 for the north Atlantic Ocean.

[6] Tropical cyclones tend to be smaller during the mid-summer, and largest in October in the Northern Hemisphere.