TC 20S(GAMANE) making landfall north of VOHEMAR/MADAGASCAR at CAT 2 US// 3 Week TC Formation Probability// 2703utc

JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 20S

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE 20S APPROACHING THE COAST OF NORTHWESTERN MADAGASCAR IN THE VICINITY OF AMPISIKANANA WITHIN A COMPETING STEERING ENVIRONMENT BETWEEN NEAR EQUATORIAL RIDGES (NER) TO THE NORTH AND EAST AND A SUBTROPICAL RIDGE TO THE SOUTH. THE SYSTEM HAS CONTINUED TO RAPIDLY INTENSIFY OVER THE LAST SIX HOURS, REVEALING A RAGGED CLOUD-FILLED EYE ON EIR. A 270013Z SSMIS 89GHZ MICROWAVE IMAGE DEPICTS A CRISP MICROWAVE EYE STRUCTURE WITH WELL-DEFINED CLOUD BANDING WRAPPING INTO THE VORTEX. AN ANTICYCLONE ALOFT PERSISTS AS THE SUBTROPICAL JET TO THE SOUTH HAS CONTINUED TO ENHANCE STRONG POLEWARD OUTFLOW AND FAVOR INTENSIFICATION. VERTICAL WIND SHEAR (VWS) REMAINS MINIMAL AT 0-5KTS AND SEA SURFACE TEMPERATURES CONTINUE TO FUEL A STRONG MOIST HEAT ENGINE. THE INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE BASED ON THE MICROWAVE IMAGERY PREVIOUSLY MENTIONED AND ANIMATED EIR DEPICTING A RAGGED EYE. THE INITIAL INTENSITY WAS ASSESSED WITH MEDIUM CONFIDENCE BASED ON EARLIER 261754Z ULTRA-HIGH RESOLUTION METOP-B SCATTEROMETRY DATA CONVEYING ELEVATED WIND SPEEDS OF 80-85KTS, AND THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: TC 20S HAS CONTINUED TO RAPIDLY INTENSIFY OVER THE LAST 12 HOURS, SO NEAR-TERM INTENSITIES ARE SET A BIT HIGHER THAN THE PREVIOUS FORECAST. FORECAST DISCUSSION: TC 20S IS FORECAST TO MAKE LANDFALL ON THE COAST OF MADAGASCAR WITHIN THE NEXT 12 HOURS AS IT REMAINS IN A COMPETING STEERING ENVIRONMENT. ONCE IT MAKES LANDFALL, THE SYSTEM IS ANTICIPATED TO ROUND THE WESTERN EDGE OF A NER TO THE EAST, INTERACTING WITH THE MOUNTAINOUS TERRAIN OF NORTHERN MADAGASCAR BEFORE BEGINNING TO CURVE TO THE SOUTHEAST BETWEEN TAU 24 AND 36, CONTINUING TO RIDE THE WESTERN PERIPHERY OF THE EASTERN NER. THE SYSTEM IS ANTICIPATED TO CONTINUE ON A SOUTHEASTERLY TRACK THROUGH THE END OF THE FORECAST PERIOD. PRIOR TO MAKING LANDFALL, THE SYSTEM IS EXPECTED TO REACH A PEAK INTENSITY ABOVE 90KTS BETWEEN TAU 0 AND TAU 12. ONCE TC 20S MAKES LANDFALL, MOIST INFLOW WILL BE RESTRICTED AND THE WESTERN PORTION OF THE SYSTEM WILL INTERACT WITH THE MOUNTAINOUS TOPOGRAPHY OF NORTHERN MADAGASCAR, INITIATING WEAKENING THROUGH THE FIRST 48 HOURS BEFORE THE SYSTEM COMES BACK OUT OVER WATER. VWS IS FORECAST TO INCREASE TO 20-25KTS BY THAT TIME, PREVENTING REINTENSIFICATION. THE SYSTEM WILL UNDERGO SUBTROPICAL TRANSITION AS IT INTERACTS WITH A CUTOFF LOW TO THE SOUTHWEST IN THE EXTENDED FORECAST PERIOD.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE HAS SOME DISAGREEMENT IN THE NEAR-TERM WITH RESPECT TO HOW FAR TC 20S WILL MOVE INTO MADAGASCAR AFTER LANDFALL. THE CROSS-TRACK ERROR AT TAU 24 IS 100NM. ADDITIONALLY, THERE APPEARS TO BE DISAGREEMENT IN HOW QUICKLY THE SYSTEM WILL TRANSIT TO THE SOUTHEAST, LIKELY DUE TO DIFFERENCES IN MODEL INTERPRETATION HOW THE NER TO THE EAST WILL RECEDE TOWARDS THE CENTRAL INDIAN OCEAN. THE INTENSITY MODEL GUIDANCE IS IN AGREEMENT THAT THE SYSTEM WILL WEAKEN OVER THE COURSE OF THE FIRST 48 HOURS, BUT THERE IS SOME DISAGREEMENT REGARDING THE RATE OF WEAKENING THEREAFTER, ALTHOUGH MOST OF THE GUIDANCE KEEPS THE SYSTEM INTENSITY ABOVE 35KTS THROUGH THE FORECAST PERIOD.

MICROWAVE IMAGE DEPICTS A CRISP MICROWAVE EYE STRUCTURE WITH WELL-DEFINED CLOUD BANDING WRAPPING INTO THE VORTEX.

GTH Outlook Discussion Last Updated - 03/26/24 Valid - 04/03/24 - 04/16/24 A robust Madden Julian Oscillation (MJO) signal has circumnavigated the globe during the past month and now resides across the Western Hemisphere (phase 1), with a well defined wave-1 asymmetry pattern in the global upper-level velocity potential field. This MJO event has led to significant upwelling across the Equatorial Pacific resulting in SSTs continuing to decrease, along with an increase of below-normal subsurface temperatures, reflective of a weakening El Nino. The MJO is forecast to return to the Indian Ocean by early April, with the CFS, GEFS, and ECMWF ensembles indicating a continued eastward propagation toward the Maritime Continent and far Western Pacific by week-3. Ensemble variability increases in the models, with some individual members weakening the MJO into the RMM-based unit circle, although others maintain a higher amplitude into mid-April. Uncertainty in the RMM-based forecast can be attributed to the 120-day mean removal which includes the +IOD event this past fall, and the uncertainty regarding the transition out of El Nino. The only tropical cyclone (TC) formation in the past week was Gamane on 3/26 just to the northeast of Madagascar. During week-2, enhanced TC development chances (20 percent or greater) are forecast to shift toward the eastern Indian Ocean and along the northern coast of Australia. Higher probabilities were considered due to MJO composites, but uncertainty in the MJO strength along with generally weak signals for TC development in the dynamical guidance supported keeping probabilities low. By week-3, dynamical guidance depicts increased signals for TC formation near and along the northern coast of Australia, and decreasing chances over the eastern Indian Ocean as more suppressed convection builds in the wake of the MJO. However, only 20 percent or greater probabilities for TC formation are indicated across the northern Australia coast as the diminishing seasonal climatology by week-3 precludes higher probabilities.