TD 25W intensifying next 48h//23W(NESAT) dissipating//Invest 93W//Invest 92B up-graded,intensifying next 72h//19E(ROSLYN)//21/09utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON 25W. 3HOURLY SATELLITE BULLETINS WERE DISCONTINUED AT 21/0530UTC ON THE REMNANTS OF 23W(NESAT).

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT TD 25W CONTINUES TO SLOWLY CONSOLIDATE BUT HAS YET TO COMMENCE SIGNIFICANT INTENSIFICATION. ANALYSIS OF THE LOW-LEVEL CLOUD LINES EXPOSED TO THE EAST OF THE CENTRAL DENSE OVERCAST (CDO) SUGGESTS THE LOW LEVEL CIRCULATION CENTER (LLCC) IS ON THE EASTERN SIDE OF THE CDO WHICH EXTENDS WESTWARD INTO THE LUZON STRAIT. SURFACE WINDS AT BASCO AND ITBAYAT ARE FROM THE NORTH AT AROUND 16-20 KNOTS, INDICATING THE SURFACE CIRCULATION REMAINS TO THEIR EAST. 21523Z AMSR2 COLORIZED 89GHZ AND 36GHZ MICROWAVE IMAGERY IS NOT CLEAR-CUT BUT DOES SHOW SOME SHALLOW SPIRAL BANDS WRAPPING INTO AN OBSCURED LLCC, WITH DEEP CONVECTION TO THE WEST. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AMSR2 MICROWAVE IMAGE. THE INITIAL INTENSITY REMAINS SET AT 30 KNOTS WITH HIGH CONFIDENCE, ON THE HIGHER END OF THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES, BUT BELOW THE MAJORITY OF THE OBJECTIVE INTENSITY ESTIMATES. THE 210523Z AMSR2 WINDSPEED PRODUCT SHOWED A LOPSIDED WIND FIELD WITH LIGHT WINDS TO THE EAST AND 25-30 KNOT WINDS TO THE WEST, PROVIDING ADDITIONAL CONFIDENCE TO THE INITIAL INTENSITY. THE SYSTEM IS MOVING AT A FAIR CLIP TOWARDS THE WEST ALONG THE SOUTHERN SIDE OF A LARGE SUBTROPICAL RIDGE (STR). UPPER-LEVEL ANALYSIS REVEALS A WEAK, MESOSCALE ANTICYCLONE HAS DEVELOPED DIRECTLY OVER OR SLIGHTLY NORTHEAST OF THE SYSTEM, PROVIDING FOR LOW VWS BUT RELATIVELY WEAK UPPER-LEVEL OUTFLOW. SSTS ARE HIGH, BUT OHC IS LOW THROUGH THE LUZON STRAIT, OFFSETTING THE OTHERWISE FAVORABLE CONDITIONS.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THE SYSTEM IS EXPECTED TO CONTINUE TRACKING WEST OF THE NEXT 24 TO 36 HOURS AS THE RIDGE COMPLEX TO THE NORTH REMAINS FIRMLY ENTRENCHED. FORWARD SPEED WILL SLOW A BIT TOWARDS TAU 36 AS A BUILDING STR CENTERED OVER THE CHINA-VIETNAM BORDER WILL TAKE OVER AS THE PRIMARY STEERING INFLUENCE. BY TAU 48, TD 25W WILL BE ON A SOUTHWESTWARD TRAJECTORY THAT WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST. TD 25W CONTINUES TO CONSOLIDATE BUT AT A SLOW PACE. PRESSURES REMAIN FAIRLY HIGH AT BASCO AND ITBAYAT (AROUND 1010 MB), MEANING THAT TD 25W HAS AN EXTREMELY SMALL INNER CORE, AND IS THUS MORE SUSCEPTIBLE TO SMALL-SCALE INFLUENCES, SUCH AS ENTRAINMENT OF RELATIVELY STABLE AIR INTO THE WESTERN SIDE OF THE SYSTEM, WHICH WILL CONTINUE TO AFFECT THE INNER STRUCTURE FOR THE NEXT 12 HOURS OR SO. THUS INTENSIFICATION IS EXPECTED TO BE SLOW, AROUND 10 KNOTS PER DAY, DUE TO THE COMPETING AND OFFSETTING INFLUENCES OF LOW VWS, WEAK UPPER-LEVEL OUTFLOW AND ENTRAINMENT OF RELATIVELY MORE STABLE AIR IN THE WESTERN PERIPHERY. THE PEAK INTENSITY HAS BEEN LOWERED TO 50 KNOTS, EXPECTED TO BE REACHED BY TAU 48. THEREAFTER, CONVERGENT FLOW ALOFT CAUSED BY THE ASYMMETRIC POSITIONING OF THE 200MB ANTICYCLONE TO THE NORTH OF THE SYSTEM, COMBINED WITH A MODEST INCREASE IN EASTERLY SHEAR, WILL COMBINE TO SMOTHER THE SYSTEM AND LEAD TO RAPID WEAKENING AFTER TAU 72. BUT THE END OF THE FORECAST THE SYSTEM IS EXPECTED TO BE NEAR LANDFALL NEAR DA NANG, VIETNAM, AS A WEAK TROPICAL DEPRESSION.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN VERY GOOD AGREEMENT, PARTICULARLY THROUGH TAU 96. THE SOLE EXCEPTION IS THE GALWEM, WHICH TURNS THE SYSTEM NORTH AT TAU 24, MAKES LANDFALL OVER CENTRAL TAIWAN AND THEN PERFORMS A HIGHLY UNLIKELY CLOCKWISE LOOP ENDING AT THE SOUTHERN TIP OF TAIWAN BY TAU 120. THE REMAINDER OF THE CONSENSUS MEMBERS ARE ENCASED WITHIN A VERY SMALL ENVELOPE, WHICH GRADUALLY EXPANDS TO JUST 50NM AT TAU 72. SPREAD INCREASES TO 190NM AT TAU 120 AS THE SYSTEM RAPIDLY WEAKENS AND THE MODELS BEGIN TO LOSE LOCK ON THE VORTEX. THE GEFS AND ECENS ENSEMBLES ARE IN TIGHT AGREEMENT HOWEVER WITH THE DETERMINISTIC MEAN, AND THUS PROVIDE HIGH CONFIDENCE TO THE JTWC FORECAST TO TAU 72, AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IN OVERALL BETTER AGREEMENT THAN THE PREVIOUS RUN, WITH ALL BUT THE COTC MODEL AGREEING ON A INTENSIFICATION TO 50 KNOTS FOLLOWED BY A FAIRLY RAPID WEAKENING THROUGH THE END OF THE FORECAST. THE HWRF INTERESTINGLY INCREASES THE INTENSITY TO 50 KNOTS BY TAU 12 THEN WEAKENS RAPIDLY THROUGH TAU 120 THOUGH THE OTHER MODELS PEAK BETWEEN TAU 36 AND TAU 48. THE JTWC FORECAST LIES AMONGST THE TIGHTEST GROUPING OF MODELS, JUST A SHADE ABOVE THE CONSENSUS MEAN WITH HIGH CONFIDENCE.

THE AREA OF CONVECTION (INVEST 92B) PREVIOUSLY LOCATED NEAR 10.3N 96.7E IS NOW LOCATED NEAR 10.9N 95.0E, APPROXIMATELY 141 NM EAST- SOUTHEAST OF PORT BLAIR, ANDAMAN ISLANDS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A PERSISTENT, BROAD ELONGATED DISTURBANCE IN THE SOUTHEASTERN REGION OF THE ANDAMAN SEA. THE SYSTEM IS EXHIBITING FRAGMENTED DEEP CONVECTION, WHICH IS OBSCURING A SLOWLY CONSOLIDATING LOW LEVEL CIRCULATION CENTER (LLCC). AN EARLIER 202303Z SSMIS MICROWAVE IMAGE REVEALS SHALLOW BANDING WRAPPING INTO AN ELONGATED LLCC POSITIONED ALONG THE SOUTHWESTERN EDGE OF A CURVED FRAGMENTED CONVECTIVE BAND. EARLIER SCATTEROMETRY DATA INDICATED AN ELONGATED LLCC WITH WIND SPEEDS UP TO 15-20 KTS ALONG THE NORTHEASTERN PERIPHERY OF THE CIRCULATION. CURRENTLY, UPPER LEVEL ANALYSIS INDICATES INVEST 92B IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE (10-15 KTS) VERTICAL WIND SHEARS (VWS), MODERATE EQUATORWARD OUTFLOW, AND WARM SEA SURFACE TEMPERATURES (27-28C). GLOBAL MODELS ARE IN GOOD AGREEMENT THAT 92B WILL CONTINUE TO TRACK GENERALLY NORTHWESTWARD AND THEN NORTHWARD, WHILE STEADILY INTENSIFYING AS THE ENVIRONMENT CONDITIONS BECOME MORE CONDUCIVE FOR FURTHER DEVELOPMENT. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1006 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.

GLOBAL MODELS ARE IN GOOD AGREEMENT THAT 92B WILL CONTINUE TO TRACK GENERALLY NORTHWESTWARD AND THEN NORTHWARD, WHILE STEADILY INTENSIFYING AS THE ENVIRONMENT CONDITIONS BECOME MORE CONDUCIVE FOR FURTHER DEVELOPMENT.

Tropical Storm Roslyn Discussion Number 6 NWS National Hurricane Center Miami FL EP192022 400 AM CDT Fri Oct 21 2022 Roslyn's structure has evolved since the previous advisory. A more distinct core of deep convection appears to be developing, and infrared satellite images have even shown hints of an eye feature during the past few hours. An elongated convective band now extends around the northeastern and southeastern quadrants of the circulation. Based on consensus Dvorak estimates of T3.5 from TAFB and SAB, and a CI number of 3.4 from the UW-CIMSS ADT, Roslyn is now estimated to have maximum winds of 55 kt. Recent scatterometer data and conventional satellite images indicate that Roslyn's center is a bit to the northeast of where it was estimated to be last evening, and the initial motion is west-northwestward, or 300/6 kt. The track forecast reasoning has not changed. Roslyn is expected to recurve around the western edge of a mid-level area of high pressure that will migrate eastward across Mexico during the next couple of days. In 2 to 3 days, Roslyn and its remnants are then expected to accelerate north-northeastward in the flow ahead of an approaching deep-layer mid-latitude trough. With the exception of the UKMET model (which is a western outlier), there is very little cross-track spread among the other track models, and most of the differences are in the forward speeds after 36 hours. The biggest change in this forecast package is that with the northeastward adjustment of Roslyn's center, the entire official track forecast has been shifted east of the previous prediction, and lies close to the updated TVCE and HCCA consensus aids. If Roslyn is indeed developing a better-defined core, environmental conditions could support rapid intensification (RI). The SHIPS RI indices are now showing a 50 to 60 percent chance of a 30-kt increase in intensity over the next 24 hours, and the HWRF, COAMPS-TC, and HCCA consensus aids are all showing RI. RI is therefore now explicitly forecast, and Roslyn should reach hurricane strength later today. In 36 to 48 hours, an increase in southwesterly shear could induce some weakening, but regardless, Roslyn is expected to reach the coast of west-central Mexico as a hurricane. Rapid weakening is expected after landfall, and although the official forecast shows a remnant low over northern Mexico in 72 hours for continuity, Roslyn is likely to have dissipated by that time. Given the relocation of Roslyn's center and the updates to the forecast, hurricane and tropical storm warnings are now in effect for portions of the west-central coast of Mexico. Hurricane watches have also been extended northward along the coast.