申論題

2. 請參下列NAVTEX所收到英文通知,並回答問題
ZCZC IB72
090520 UTC JUL 24
WWJP73 RJTD 090000
IMPORTANT WARNING FOR YOKOHAMA NAVTEX AREA
090000UTC ISSUED AT 090300UTС
WARNING (DENSE FOG) EASTERN SEA OFF SANRIKU, WESTERN SEA OFF
SANRIKU, NORTHERN SEA OFF KANTO POOR VISIBILITY 0.3 MILES OR LESS
IN PLACES
NEXT WARNING WILL BE ISSUED BEFORE 090900UTC
NNNN

2.3 信文中「NNNN」所代表之意義與功能為何? (5分)