Wednesday, the ghost of Hurricane Barbara, sapped of its strength by cool waters, approached Hawaii with some of its moisture intact. Flash flood watches were posted around Hilo.
The coolness of the seas that saps the wind strength of eastern Pacific hurricanes can be traced to salty water. The ocean south and east of Hawaii is a desert, with little rain to dilute surface waters. Also, seawater continually evaporates under sunshine, leaving salt behind. As a result, surface waters are salty and dense, causing them to sink. In compensation, cooler water rises to the surface from below.