WTIO21 PGTW 280930 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE FORMATION ALERT// RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 055 NM EITHER SIDE OF A LINE FROM 21.3N 88.9E TO 22.9N 87.5E WITHIN THE NEXT 00 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO BE 28 TO 33 KNOTS. METSAT IMAGERY AT 280600Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 21.3N 88.9E. THE SYSTEM IS MOVING NORTHWESTWARD AT 07 KNOTS. 2. REMARKS: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT INVEST 98B CONTINUES TO RAPIDLY CONSOLIDATE, WITH BANDS OF DEEP CONVECTION NOW WRAPPING INTO A WELL-DEFINED CENTER JUST OFFSHORE SOUTH OF KOLKATA, INDIA. ANIMATED RADAR DATA FROM INDIA INDICATES THE PRESENCE OF A WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) WITH MODERATE TO STRONG CONVECTIVE BANDS, PARTICULARLY ON THE SOUTHEAST SIDE, WRAPPING INTO AND AROUND THE LLCC. SIMILARLY AT 280726Z AMSR2 89 GHZ MICROWAVE IMAGE SHOWS DEVELOPMENTAL BANDING WRAPPING INTO THE CENTER DEFINED BY A LOW EMISSIVITY REGION. A PREVIOUS 280246Z ASCAT-B AND 280314Z ASCAT-C PASS INDICATED 30-35 KNOT WINDS WITH SOME HIGHER WINDS UNDER DEEP CONVECTION IN THE EASTERN SEMICIRCLE, THOUGH WINDS IN THE REMAINDER OF THE CIRCULATION WERE 25 KNOTS OR LESS. THE ENVIRONMENT IS FAVORABLE FOR DEVELOPMENT, WITH AN ANTICYCLONE ALOFT JUST TO THE NORTHEAST PROVIDING GOOD RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR. SSTS REMAIN VERY WARM. WHILE THE SYSTEM IS CURRENTLY MOVING ONSHORE, IT WILL DO SO OVER A REGION OF SWAMPY GROUND IN A RIVER DELTA. THUS INTENSIFICATION OVER LAND IS A DISTINCT POSSIBILITY. NUMERICAL MODEL GUIDANCE IS CURRENTLY LIMITED, BUT GENERALLY AGREES ON SLOW BUT STEADY NORTHWEST MOVEMENT OVER THE NEXT 24 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 28 TO 33 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 998 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS HIGH. 3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 290930Z. // NNNN