WWJP73 RJTD 180600 IMPORTANT WARNING FOR YOKOHAMA NAVTEX AREA 180600UTC ISSUED AT 180900UTC WARNING(DENSE FOG) EASTERN SEA OFF SANRIKU, WESTERN SEA OFF SANRIKU, NORTHERN SEA OFF KANTO, SOUTHERN SEA OFF KANTO, EASTERN SEA OFF TOKAI, SOUTHERN SEA OFF TOKAI POOR VIS 0.3 MILES OR LESS IN PLACES NXT WARNING WILL BE ISSUED BEFORE 181500UTC =