TC 05S(DARIAN) CAT 1 US: has been intensifying faster than forecast//Invest 93W//Invest 98B// 19/12utc

JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 05S(DARIAN).

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: FORECAST TRACK SPEEDS FOR THE TAU 72 TO TAU 120 PERIOD HAVE SLOWED FROM THE PREVIOUS WARNING CONSISTENT WITH CONSENSUS MODEL GUIDANCE. HOWEVER, THE OVERALL FORECAST PHILOSOPHY REMAINS THE SAME. FORECAST DISCUSSION: TC 05S WILL CONTINUE TO TRACK SLOWLY SOUTHEASTWARD TO POLEWARD OVER THE NEXT 24 HOURS UNDER THE CONTINUED STEERING INFLUENCE OF THE NEAR EQUATORIAL RIDGE TO THE NORTHEAST. AFTER TAU 24, A BUILDING SUBTROPICAL RIDGE TO THE SOUTH IS EXPECTED TO TAKE OVER AS THE DOMINANT STEERING MECHANISM AND PUSH TC 05S ON A GENERALLY WESTWARD TRAJECTORY THROUGH THE REMAINDER OF THE FORECAST PERIOD. CONTINUED, STEADY INTENSIFICATION THROUGH TAU 24 IS LIKELY GIVEN FAVORABLY LOW VERTICAL WIND SHEAR AND A SUPPORTIVE POLEWARD OUTFLOW PATTERN. HOWEVER, THE MAGNITUDE OF ADDITIONAL INTENSIFICATION WILL BE LIMITED AS THE SLOW-MOVING SYSTEM PASSES OVER A SHALLOW LAYER OF 26-27C WATER AND CONTENDS WITH INDUCED UPWELLING OF COOLER WATER. AFTER TAU 24, THE SYSTEM IS EXPECTED TO WEAKEN SLIGHTLY PRIMARILY DUE TO MORE RESTRICTED UPPER-LEVEL OUTFLOW AND CONTINUED PASSAGE OVER MARGINAL SEA SURFACE TEMPERATURES. A SLIGHT UPTICK IN THE INTENSITY LATE IN THE FORECAST PERIOD IS POSSIBLE AS THE SYSTEM DIPS A BIT POLEWARD AROUND THE STEERING RIDGE AND OUTFLOW AGAIN IMPROVES.

MODEL DISCUSSION: NUMERICAL MODELS REMAIN IN AGREEMENT REGARDING THE OVERALL FORECAST SCENARIO OF INITIALLY POLEWARD MOTION THROUGH TAU 24 TO 36, FOLLOWED BY A TURN TOWARD THE WEST. MODEL SPREAD IS FAIRLY LIMITED THROUGH TAU 72, BUT INCREASES THEREAFTER AS DEPICTED EVOLUTION OF THE SUBTROPICAL STEERING RIDGE VARY. IT IS TOO EARLY TO TELL WHETHER THE RIDGE WILL REMAIN SOLIDLY IN PLACE TO THE SOUTH OF TC 05S OR A BREAK WILL DEVELOP ALLOWING THE SYSTEM TO DIP FARTHER POLEWARD AFTER TAU 72 THAN CURRENTLY ANTICIPATED. THE CURRENT FORECAST TRACK LIES NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE, NEAR THE MULTIPLE MODEL CONSENSUS AND ECMWF MODEL SOLUTIONS. INTENSITY FORECAST GUIDANCE IS ALSO IN FAIR AGREEMENT FOR THE FIRST 72 HOURS OF THE FORECAST GIVEN THE FAIRLY STRAIGHTFORWARD SET OF ENVIRONMENTAL INFLUENCES. AS EXPECTED, HOWEVER, DEPICTIONS OF INTENSITY IN THE LATER TAUS VARY SIGNIFICANTLY DEPENDING ON THE MODEL-PREDICTED SYNOPTIC ENVIRONMENTS.