WWJP71 RJTD 171800 IMPORTANT WARNING FOR NAHA NAVTEX AREA 171800UTC ISSUED AT 172100UTC PRESSURE GRADIENT IS STEEP WARNING(NEAR GALE) SEA SOUTH OF OKINAWA WARNING(DENSE FOG) SOUTHERN PART OF EAST CHINA SEA POOR VIS 0.3 MILES OR LESS IN PLACES NXT WARNING WILL BE ISSUED BEFORE 180300UTC =