TD 27W: forecast to reach Typhoon/CAT 4 by 72hours//Invest 94W: forecast significant deepening over the Andaman Sea,29/15utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TD 27W.

3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TD 27W IS FORECAST TO TRACK WEST-NORTHWESTWARD THROUGH 36H UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE(STR) POSITIONED TO THE NORTH. AFTER 36H, A DEEP MIDLATITUDE TROUGH IS FORECAST TO DIG INTO THE EAST CHINA SEA, WHICH WILL WEAKEN THE STR AND REALIGN THE STR TO A MORE POLEWARD CONFIGURATION. AS THE SYSTEM TURNS MORE POLEWARD BETWEEN 36H TO 48H IT IS EXPECTED TO SLOW AS IT ENCOUNTERS A STRONG NORTHEAST SURGE EVENT. THEN GRADUALLY ACCELERATE NORTH-NORTHEASTWARD AS THE SURGE EVENT WEAKENS BY 72H. RAPID INTENSIFICATION IS ANTICIPATED AFTER 48H DUE TO STRONG POLEWARD OUTFLOW INTO THE AFOREMENTION MIDLATITUDE TROUGH. THE SYSTEM SHOULD PEAK AT 115 KNOTS/CAT 4 BY 72H DUE TO VERY FAVORABLE ENVIRONMENTAL CONDITIONS. AFTER 72H, TD 27W WILL TRACK NORTH-NORTHEASTWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE STR THROUGH 120H. AFTER 72H, STEADY WEAKENING WILL OCCUR AS VERTICAL WIND SHEAR INCREASES TO 25 TO 30 KNOTS.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH IMPROVED CONVECTIVE BANDING WRAPPING INTO A RAGGED LOW-LEVEL CIRCULATION CENTER. UNFORTUNATELY, THERE IS NO USEFUL MICROWAVE IMAGERY OR SCATTEROMETRY IMAGERY AVAILABLE, THEREFORE, THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE AND IS HEDGED ABOVE THE PGTW AND KNES DVORAK ESTIMATES. WITH THE EXCEPTION OF THE EASTERN QUADRANT, OUTFLOW IS VIGOROUS WITH POLEWARD OUTFLOW ENHANCED BY STRONG WESTERLY FLOW TO THE NORTH. ADDITIONALLY, VERTICAL WIND SHEAR IS LOW.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH 72H WITH THE EXCEPTION OF NAVGEM, THE SOLE OUTLIER, WHICH TRACKS THE SYSTEM WESTWARD THEN SLOWLY NORTH-NORTHWESTWARD. AFTER 72H, THERE IS A HIGH DEGREE OF UNCERTAINTY (LOW CONFIDENCE) IN THE JTWC FORECAST TRACK. SEVERAL MODELS (GFS, GFS ENSEMBLE MEAN, UKMET ENSEMBLE MEAN) INDICATE THE SYSTEM WILL SLOW AND STALL AS A LOW-LEVEL RIDGE BUILDS TO THE NORTH AND A FRONTAL SYSTEM RAPIDLY PUSHES EASTWARD. THE GFS ENSEMBLE (GEFS) SHOWS A BIFURCATION WITH THE BULK OF THE SOLUTIONS STALLING AND TRACKING TOWARD AND OVER THE PHILIPPINES AFTER 120H. THE ECMWF DETERMINISTIC SOLUTION DEPICTS A RAPID NORTH-NORTHEASTWARD TRACK AND IS THE FASTEST MODEL AT THIS TIME. THE ECMWF ENSEMBLE AT 290600Z, HOWEVER, SHOWS ONLY A FEW SOLUTIONS WITH A SIMILAR FAST POLEWARD TRACK. THE BULK OF THE EPS SOLUTIONS ARE STALLING AND SLOWING BETWEEN 21N AND 24N. THE ECMWF DETERMINISTIC SOLUTION APPEARS UNLIKELY DUE TO THE BUILDING RIDGE TO THE NORTH AND LACK OF A FRONTAL SYSTEM SO THE JTWC FORECAST FAVORS THE GFS DETERMINISTIC MODEL SOLUTION AT THIS TIME.

HIGH, VERY FAVORABLE OCEAN HEAT CONTENT VALUES.

THE AREA OF CONVECTION (INVEST 94W) PREVIOUSLY LOCATED NEAR 7.9N 106.0E IS NOW LOCATED NEAR 7.9N 105.2E, APPROXIMATELY 355 KM SOUTHWEST OF HO CHI MINH, VIETNAM. ANIMATED MULTISPECTRAL SATELLITE IMAGERY REVEALS A BROAD BUT SLOWLY CONSOLIDATING LLC. A 290012Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS IMPROVED DEEP CONVECTIVE BANDING OVER THE SOUTHERN SEMICIRCLE. A 290240Z ASCAT-B IMAGE SHOWS A DEFINED, ELONGATED CIRCULATION WITH 20-25 KNOT WINDS OVER THE EASTERN QUADRANT. UPPER-LEVEL ANALYSIS INDICATES THAT THE SYSTEM IS IN A MARGINALLY FAVORABLE ENVIRONMENT DEFINED BY LOW TO MODERATE VWS AND GOOD POLEWARD OUTFLOW. ADDITIONALLY, WARM (29-30C) SEA SURFACE TEMPERATURES ARE CONDUCIVE FOR DEVELOPMENT. THE BULK OF THE GLOBAL MODELS ARE IN GENERAL AGREEMENT REGARDING THE WESTWARD TRACK OF 94W ACROSS THE STRAIT OF MALACCA INTO THE BAY OF BENGAL WITH SIGNIFICANT DEVELOPMENT IN THE ANDAMAN SEA. THE ECMWF DETERMINISTIC MODEL, HOWEVER, INDICATES SLOWER DEVELOPMENT AND A WEAKER SYSTEM. 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 REMAINS MEDIUM.

THE BULK OF THE GLOBAL MODELS ARE IN GENERAL AGREEMENT REGARDING THE WESTWARD TRACK OF 94W ACROSS THE STRAIT OF MALACCA INTO THE BAY OF BENGAL WITH SIGNIFICANT DEVELOPMENT IN THE ANDAMAN SEA. THE ECMWF DETERMINISTIC MODEL, HOWEVER, INDICATES SLOWER DEVELOPMENT AND A WEAKER SYSTEM.