Very small TC 08S(BATSIRAI) under-went a very rapid intensifcation span// Invest 91W is Medium// Invest 97P, 27/15utc

JTWC IS ISSUING 12HOURLY WARNINGS ON TC 08S(BATSIRAI) AND 3HOURLY SATELLITE BULLETINS ON 08S AND INVEST 91W.

27/14UTC.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: DUE TO THE RAPID INTENSIFICATION PHASE, THERE ARE MAJOR CHANGES IN THE JTWC INTENSITY FORECAST. FORECAST DISCUSSION: TC 08S IS FORECAST TO TRACK WEST-SOUTHWESTWARD THROUGH 48H ALONG THE NORTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR). AFTER 48H, A MIDLATITUDE SHORTWAVE TROUGH WILL WEAKEN THE STR, WHICH WILL LEAD TO A SLIGHT DECREASE IN FORWARD MOTION. TC 08S IS EXPECTED TO WEAKEN STEADILY THROUGH 36H BUT SHOULD REINTENSIFY AS POLEWARD OUTFLOW IMPROVES FROM 48H TO 72H. AFTER 72H, TC 08S WILL TURN WESTWARD TO WEST-NORTHWESTWARD AS IT TRANSITIONS TO THE STEERING INFLUENCE OF A WESTERN STR BUILDING TO THE SOUTHWEST AFTER THE MIDLATITUDE SHORTWAVE TROUGH PROPAGATES EASTWARD. UPPER-LEVEL CONDITIONS ARE EXPECTED TO DEGRADE WITH INCREASING VERTICAL WIND SHEAR (20 TO 25 KNOTS) AND WEAK DIFFLUENCE ALOFT THUS STEADY WEAKENING IS ANTICIPATED.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TC 08S HAS RAPIDLY INTENSIFIED (55 KNOTS) OVER THE PAST 12 HOURS, INCREASING FROM 35 KNOTS AT 270000Z TO THE INITIAL INTENSITY OF 90 KNOTS/CAT 2 US AT 271200Z. THE SYSTEM IS CLASSIFIED AS A VERY SMALL SYSTEM WITH A SMALL CENTRAL DENSE OVERCAST FEATURE. TC 08S DEVELOPED AN EYE AT ABOUT 270900Z AND MAINTAINED A SMALL (13KM) ROUND EYE AT 271200Z, WHICH LED TO A MAJOR JUMP IN DVORAK ESTIMATES FROM T2.5-3.0 (35-45 KNOTS) AT 270600Z TO THE CURRENT DVORAK ESTIMATES RANGING FROM T5.0-T5.5 (90-102 KNOTS). THIS RAPID INCREASE IS TYPICAL OF VERY SMALL SYSTEMS. CURRENTLY, ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A GRADUAL WEAKENING TREND AND LOSS OF THE EYE FEATURE SINCE 271200Z. A 271311Z SSMIS 91GHZ IMAGE INDICATES A SMALL CORE OF CENTRAL CONVECTION WITH SPIRAL BANDING OVER THE SOUTHERN SEMICIRCLE. UPPER-LEVEL ANALYSIS INDICATES A VERY FAVORABLE ENVIRONMENT WITH STRONG RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH 48H WITH A 150KM SPREAD IN SOLUTIONS AT 48H. AFTER 48H, THE NUMERICAL MODELS DIVERGE SIGNIFICANTLY WITH LARGE SPREAD AND HIGH UNCERTAINTY. NAVGEM AND AFUM ARE OUTLIERS INDICATING A SOUTHWARD TRACK, WHICH IS ASSESSED AS UNLIKELY, HOWEVER, THE REMAINING GUIDANCE SHOWS SOLUTIONS TRACKING SOUTHEAST OF LA REUNION TO NORTH OF LA REUNION. THE 270600Z ECMWF ENSEMBLE (EPS) ALSO INDICATES A LARGE SPREAD IN ENSEMBLE SOLUTIONS. THERE IS A LARGE DEGREE OF UNCERTAINTY IN THE JTWC INTENSITY FORECAST DUE TO THE VERY SMALL SYSTEM SIZE AND POTENTIAL FOR RAPID INTENSITY CHANGES.

THE AREA OF CONVECTION (INVEST 91W) PREVIOUSLY LOCATED NEAR 8.4N 121.4E IS NOW LOCATED NEAR 9.4N 115.4E, APPROXIMATELY 370 KM WEST OF PUERTO PRINCESA, PHILIPPINES. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS LOW-LEVEL CLOUD LINES WRAPPING INTO A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) WITH FLARING BURSTS OF DEEP CONVECTION OVER THE SYSTEM. A 270441Z GMI 37GHZ MICROWAVE IMAGE SHOWS FRAGMENTED, FORMATIVE CONVECTIVE BANDS OVER THE SOUTHERN AND NORTHERN SEMICIRCLES WITH A RAGGED, ILL-DEFINED LLCC. HOWEVER, A 270221Z ASCAT-B IMAGE SHOWS A DEFINED CIRCULATION WITH 15-20 KNOT WINDS OVER THE NORTHERN SEMCIRCLE AND 5-10 KNOT WESTERLIES OVER THE SOUTHERN SEMICIRCLE. UPPER-LEVEL CONDITIONS ARE MARGINALLY-FAVORABLE WITH MODERATE TO HIGH (20-25 KNOTS) VERTICAL WIND SHEAR OFFSET BY STRONG DIFFLUENCE ALOFT. SEA SURFACE TEMPERATURES ARE CONDUCIVE AT 28-30C. GLOBAL MODELS INDICATE NO SIGNIFICANT DEVELOPMENT AS THE SYSTEM TRACKS SLOWLY POLEWARD, HOWEVER, THERE IS SOME POTENTIAL FOR A WEAK TROPICAL DEPRESSION TO FORM ADJACENT TO A NORTHEAST SURGE EVENT. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1005 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.

GLOBAL MODELS INDICATE NO SIGNIFICANT DEVELOPMENT AS THE SYSTEM TRACKS SLOWLY POLEWARD, HOWEVER, THERE IS SOME POTENTIAL FOR A WEAK TROPICAL DEPRESSION TO FORM ADJACENT TO A NORTHEAST SURGE EVENT.