TC 18S forecast to reach CAT 1 US within 48H//TC 19P(MEGAN) remnants over-land // 3 Week TC Formation Probability//2003utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 18S. 3 HOURLY SATELLITE BULLETINS ARE STILL ISSUED ON THE OVER-LAND REMNANTS OF TC 19P

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS REDEVELOPMENT OF WELL DEFINED SPIRAL BANDING WRAPPING INTO A CONSOLIDATING MASS OF DEEP CONVECTION, WITH HOT TOWERS CONCENTRATING OVER THE SUSPECTED AREA OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE BYU HIGH RESOLUTION ENHANCEMENT OF THE 191426Z ASCAT-C PASS INDICATED 30 KT MAXIMUM WINDS, HOWEVER, THE WESTERN PERIPHERY WAS NOT COMPLETELY IN THE FOOTPRINT. A 191814Z AMSR2 37V PASS REVEALED A WELL DEFINED LOW LEVEL CENTER FEATURE, WITH GENERALLY SYMMETRIC BANDING. COMPARISON WITH THE 89 GHZ CHANNEL INDICATES THERE IS A NORTH-SOUTH TILT IN THE VORTEX, HOWEVER, THE DEGREE OF TILT HAS BEEN GRADUALLY DECREASING. COMBINED WITH THE IMPROVED CONVECTIVE CORE IN THE MSI, VERTICAL WIND SHEAR (VWS) IS ASSESSED TO BE DECREASING, OR TC 18S IS BEGINNING TO SUCCESSFULLY PUSH BACK AGAINST THE ENVIRONMENTAL SHEAR. A RARE SUBSEQUENT STRING OF GOOD-COVERAGE SSMIS AND COWVR PASSES PROVIDES A TIME SERIES OF DEVELOPMENT AND LENDS GOOD CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY WAS ASSESSED AT 35 KTS, BASED ON DVORAK T2.5 FINAL-T ESTIMATES FROM ALL REPORTING AGENCIES, AND IS SUPPORTED BY CIMSS ADT, AIDT, AND DPRINT. POLEWARD OUTFLOW IS BEING MODERATELY ENHANCED BY A JET TO THE SOUTHEAST, AND SSTS ARE A FAVORABLE 27 TO 28 DEGREES CELSIUS. THE PRIMARY LIMITING FACTOR AT THIS TIME IS THE LACK OF A SOURCE OF MID-LEVEL MOISTURE. GFS AND ECMWF ANALYSES INDICATES TC 18S IS NEARLY SURROUNDED BY DRY AIR, HOWEVER, A POCKET OF DEEP CENTRAL MOISTURE IS PREVENTING DRIER AIR FROM PENETRATING THE CORE.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: RESUMING JTWC WARNINGS BASED ON ANALYSIS OF ALL AVAILABLE DATA INDICATING TC 18S HAS REACHED 35 KNOT WARNING CRITERIA. FORECAST DISCUSSION: TC 18S IS FORECAST TO TRACK WESTWARD THROUGH TAU 48 UNDER THE INFLUENCE OF THE STEERING RIDGE TO THE SOUTH. INTENSIFICATION IS EXPECTED TO BE GRADUAL OVER THE FIRST 24 HOURS AS THE VORTEX ALIGNMENT CONTINUES TO IMPROVE, AND PERSISTENT CONVECTION ENHANCES THE MOISTURE IN THE IMMEDIATE VICINITY OF THE LLCC, ALTHOUGH DRY AIR IS EXPECTED TO REMAIN ENTRENCHED AROUND THE PERIPHERY. AFTER 24 HOURS, MODELS ARE INDICATING A PERIOD OF STRONG DEEPENING, NEARING RAPID INTENSIFICATION PACE, AS VWS SHOULD REMAIN FAVORABLE. PEAK INTENSITY WAS SET AT 75 KNOTS, WHICH HELD BELOW THE AGGRESSIVE MESOSCALE MODELS, GIVEN THAT AVAILABLE MOISTURE SHOULD REMAIN A LIMITING FACTOR. BEYOND TAU 48, THE TRACK WILL TRANSITION TO SOUTHWESTWARD, AS A WEAKNESS DEVELOPS IN THE STR. AFTER TAU 72, THE SYSTEM WILL BEGIN FEELING THE EFFECTS OF INCREASED VWS DUE TO AN APPROACHING UPPER LEVEL JET. ADDITIONALLY, SSTS WILL DROP BELOW 26 DEGREES CELSIUS. VWS WILL CONTINUE TO INCREASE THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. THE FIVE DAY FORECAST INTENSITY IS SET AT 35 KTS, HOWEVER, DISSIPATION MAY OCCUR SOONER DUE TO THE HIGHLY UNFAVORABLE ENVIRONMENT ANTICIPATED BY THAT TIME.

MODEL DISCUSSION: MODEL GUIDANCE IS SOMEWHAT LIMITED FOR THIS FIRST ROUND OF REGENERATED WARNINGS. HOWEVER, GFS, GEFS, AND HAFS ARE IN TIGHT AGREEMENT, AND ALTHOUGH FASTER THAN THE ECWMF AND ITS ENSEMBLE, THE TRACK PATTERNS ARE GENERALLY THE SAME. GIVEN THE LIMITED MODELS, 0-72 HOUR TRACK CONFIDENCE IS ASSESSED AS MEDIUM, AND THE EXTENDED TRACK CONFIDENCE IS SET TO LOW. THESE ASSESSMENTS SHOULD IMPROVE IF MODEL AGREEMENT CONTINUES TO BE OBSERVED. INTENSITY CONFIDENCE IS SET TO LOW, WHILE ASSESSING IF THIS CURRENT ROUND OF IMPROVEMENT CAN SUSTAIN ITSELF FOR MORE THAN 6 HOURS.

GTH Outlook Discussion Last Updated - 03/19/24 Valid - 03/27/24 - 04/09/24 A robust MJO event continues to unfold, with the enhanced convective phase now crossing the Western Pacific. During the past week or so, widespread enhanced convection overspread the eastern Indian Ocean and western Maritime Continent, which is a departure from the weakening ENSO base state. Dynamical models are in good agreement with tight ensemble clustering that strong MJO activity continues to propagate eastward from the Western Pacific and into Western Hemisphere over the next two weeks, though it should be noted that the forecasted phase speed is on the fast end of the MJO frequency range . As the suppressed phase of the MJO is moving into the Maritime Continent, this tends to suppress tropical cyclone (TC) activity in the Australia and South Pacific regions, which have been active recently. One TC formed over the last week. On March 15 TC Megan formed in the Gulf of Carpentaria. It intensified quickly, reaching category 3 strength, and came ashore into northern Australia on March 18. The Joint Typhoon Warning Center (JTWC) expects Megan to dissipate in the next day or so, but indicate that the system will be closely monitored for signs of regeneration. Consensus among the model ensembles depicts the MJO in phases 8 and 1 during week-2, which would slightly favor TC genesis in the southwest Indian Ocean. This is also supported by the ECMWF extended range TC genesis forecast, so a slight risk (>20% probability) for TC genesis is posted east of Madagascar. The MJO in phase 8 or 1 tends to suppress TC activity for the Australia and South Pacific regions, which have been quite active lately. Model solutions diverge by week-3 but generally still indicate eastward propagation of the MJO signal into the Indian Ocean, which would once again begin to favor TC genesis off the northwest coast of Australia for week-3.