navigable semicircle

navigable semicircle

[′nav·i·gə·bəl ′sem·i‚sər·kəl]
(meteorology)
That half of a cyclonic storm area in which the rotary and progressive motions of the storm tend to counteract each other, and the winds are in such a direction as to blow a vessel away from the storm track.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.