ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM Hurricane Simon Discussion Number 21 NWS National Hurricane Center Miami FL EP202026 800 AM MST Mon Oct 12 2026 Simon's interaction with the coast of Mexico has made it a very compact hurricane. The satellite presentation this morning consists of a very small central dense overcast with a warm spot in the center which still appears to be a small eye. The convection is also very electrically active, with substantial lightning occurring in the eastern eyewall. A 1110 UTC GPM microwave pass showed that Simon's inner core remains intact, though with the eye open on the northwest side. This structure is consistent with some mid-level easterly shear that appears to be undercutting the outflow layer, looking at some area-average soundings from the HAFS-A/B initialization this morning. Satellite intensity estimates have a large range this morning, as low as CI 4.1/67 kt from the UW-CIMSS ADT, or as high as CI 5.5/102 kt from the latest subjective Dvorak fix. The initial intensity is lowered slightly to 95 kt for this advisory, favoring a blend of the latest SATCON (100 kt) and D-MINT (85-90 kt) estimates. Based on satellite images, Simon continues to move very slowly to the northwest, with an estimated motion of 315 degrees at 3 kt. This very slow motion is the result of competing steering influences from a distant mid-level ridge centered over the Texas Gulf coast, and another weaker mid-level ridge placed southwest of Simon over the eastern Pacific. In general the steering imparted by the ridge to the northwest should be a little stronger, and thus Simon is expected to maintain a very slow northwestward motion over the next 24-36 h. After that period, a large trough with an embedded short-wave is expected to amplify and move into the southwestern United States, and this trough is expected to extend far enough southward to impart a little more westerly flow that should ultimately turn Simon to the north-northeast in the 48-72 hour time frame. With that said, the track guidance is not at all in agreement on how quickly this turn will occur. The latest 06 UTC GFS and HAFS-A/B runs almost immediately move Simon northward and then north-northeast, resulting in a much faster landfall back in mainland Mexico. By contrast, the 06 UTC ECMWF run shows a short-term westward track that meanders offshore to the southeast of the Baja California Peninsula before it turns northward and moves up into the Gulf of California. The ensemble guidance is also all over the place, resembling a squashed spider with substantial spread from the southwest to northeast direction. The latest NHC track forecast has been shifted westward and is quite a bit slower, following the latest trends in the track guidance. However, this track is not nearly as slow or as far west as the latest Google DeepMind ensemble mean (GDMI) or its newer Weather Next Model (WN3I). Given the large spread in solutions, this remains a low confidence track forecast. Based on the earlier microwave images, Simon still appears to have a small inner core, and that is an important consideration to take into account in the forecast over the next few days. While the hurricane appears to be currently dealing with some mid-level easterly shear and that may result in a little more short-term weakening, this shear is expected to subside over the next 24 h as Simon traverses very warm 30-31 C sea-surface temperatures. In fact, the latest HMON and HAFS-A/B runs show the small core of Simon recovering and re-intensifying back into a major hurricane later this week. Thus, the latest NHC intensity forecast starts to show some restrengthening after 24 h. Small storms like Simon can also be prone to rapid changes in intensity, both up or down, which makes the intensity forecast also more uncertain than usual. This forecast is initially close to the middle of the guidance but ends up on the higher side after 48 h. R…

WDPN33 PGTW 121500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 031// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 31.4N 148.6E INITIAL INTENSITY: 80 KTS GEOGRAPHIC REFERENCE: 503 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 18 KTS SIGNIFICANT WAVE HEIGHT: 38 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: THE CONVECTIVE STRUCTURE OF TYPHOON (TY) 27W HAS SIGNIFICANTLY DEGRADED OVER THE PAST SIX HOURS. THE EYE IS NO LONGER EVIDENT IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY. INSTEAD, A RAGGED CENTRAL DENSE OVERCAST (CDO) IS DISPLACED FROM THE LOW-LEVEL CIRCULATION CENTER (LLCC), INDICATING AN INCREASINGLY VERTICALLY TILTED VORTEX. THIS TILT IS EVIDENT IN A COMPARISON OF THE 120816Z WSF-M MWI 89 GHZ AND 37 GHZ IMAGES, WHICH REVEAL A NORTHEASTWARD DISPLACEMENT WITH HEIGHT. THE SYSTEM IS STRADDLING THE 26-DEGREE CELSIUS ISOTHERM, AND SOUTHWESTERLY VERTICAL WIND SHEAR (VWS) HAS INCREASED TO 20-30 KTS. EQUATORWARD OUTFLOW IS RESTRICTED, WHILE TY 27W IS PHASING WITH THE RIGHT-FRONT ENTRANCE REGION OF A JET STREAK, LEADING TO STRONG POLEWARD OUTFLOW. OVERALL, THE ENVIRONMENT IS HIGHLY UNFAVORABLE. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE, HEDGED SOUTHWEST OF THE UPPER-LEVEL CIRCULATION CENTER AND EXTRAPOLATED FROM A 121111Z ASCAT-B IMAGE. WITH THE SIGNIFICANTLY DETERIORATED CONVECTIVE SIGNATURE IN EIR, THE INITIAL INTENSITY HAS BEEN LOWERED TO 80 KTS WITH MEDIUM CONFIDENCE, SUPPORTED BY THE STEADILY DECREASING SUBJECTIVE AND OBJECTIVE ESTIMATES RANGING FROM 77 KTS TO 92 KTS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: NORTHWESTERN FLANK OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED NEAR 28N 164E AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS RJTD: T5.0 - 90 KTS RCTP: T4.5 - 77 KTS CIMSS ADT: 82 KTS AT 121140Z CIMSS AIDT: 92 KTS AT 121140Z CIMSS D-MINT: 82 KTS AT 120818Z CIMSS D-PRINT: 77 KTS AT 121140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE VWS: 20-30 KTS SST: 25-26 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED FROM 72 HOURS TO 60 HOURS. FORECAST DISCUSSION: TY 27W IS NOW TRAVELING NORTH-NORTHEASTWARD AT 18 KTS ALONG THE NORTHWESTERN PERIPHERY OF A STR. THE SYSTEM WILL CONTINUE TO ACCELERATE AS IT BECOMES INCREASINGLY EMBEDDED IN DEEP-LAYER WESTERLY FLOW. THE ENHANCED POLEWARD OUTFLOW IS NOT SUFFICIENT TO OFFSET THE HIGHLY DETRIMENTAL EFFECTS OF VWS AND MARGINAL SEA SURFACE TEMPERATURES (SST). SHEAR WILL INCREASE TO 35-45 KTS BY TAU 24 AND 45-55 KTS BY TAU 48, WHILE THE SST WILL DROP BELOW 25 DEGREES CELSIUS NEAR TAU 12. THESE HOSTILE CONDITIONS WILL MAINTAIN A STEADY TO RAPID WEAKENING TREND THROUGH TAU 24. TY 27W WILL GRADUALLY ENTER THE BAROCLINIC ZONE, BEGIN EXTRATROPICAL TRANSITION (ETT) AT TAU 48, AND COMPLETE ETT BY TAU 60. AS THIS OCCURS, THE RATE OF WEAKENING WILL SLOW AS THE SYSTEM BROADENS OUT AND ACQUIRES FRONTAL CHARACTERISTICS. MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN EXCELLENT AGREEMENT, WITH A CROSS-TRACK SPREAD OF 70 NM AT TAU 24 AND 110 NM AT TAU 48. NAVGEM AND ECMWF ARE THE MOST POLEWARD MODELS, WITH NAVGEM BEING THE FASTEST. DESPITE THESE MODEST DIFFERENCES, THE ALONG-TRACK SPREAD IS MINIMAL, AND THE REMAINING GUIDANCE MEMBERS ARE TIGHTLY CLUSTERED. THE JTWC FORECAST TRACK HAS SHIFTED BY APPROXIMATELY 10 NM THROUGH TAU 60, REPRESENTING A NEARLY UNCHANGED TRACK COMPARED TO THE PREVIOUS FORECAST. THE TRACK IS POSITIONED WITH HIGH CONFIDENCE ALONG A BLEND OF THE MULTI-MODEL CONSENSUS AND GOOGLE DEEPMIND. DEEPMIND HAS CONSISTENTLY DEPICTED RAP…

WDPN31 PGTW 121500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.1N 149.1E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 317 NM NORTHEAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 11 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS PERSISTENT DEEP CONVECTION CONFINED TO THE SOUTHERN PERIPHERY OF THE COMPACT LOW-LEVEL CIRCULATION CENTER (LLCC). OVER THE PAST SIX HOURS, THE LOW-LEVEL CLOUD LINES ALONG THE EASTERN SIDE HAVE ACCELERATED, SUGGESTING IMPROVED LOW-LEVEL ROTATION. A 121108Z ASCAT-B PASS REVEALS AN OBLONG, CLOSED WIND FIELD WITH A PATCH OF 25-30 KT WINDS IN THE SOUTHERN SEMICIRCLE. TROPICAL DEPRESSION (TD) 28W HAS BECOME BETTER ORGANIZED WHILE TRAVERSING WARM SEA SURFACE TEMPERATURES (SST) OF 28-29 DEGREES CELSIUS IN AN OTHERWISE MARGINAL ENVIRONMENT OF DRY AIR AND NORTHERLY VERTICAL WIND SHEAR (VWS) OF 15-20 KTS, LARGELY ASSOCIATED WITH A TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT) JUST TO THE WEST. BASED ON THE SLIGHT IMPROVEMENT IN STORM STRUCTURE AND THE SCATTEROMETER DATA, THE INITIAL INTENSITY IS RAISED TO 30 KTS WITH HIGH CONFIDENCE. THE INITIAL POSITION IS ALSO PLACED WITH HIGH CONFIDENCE BASED ON EXTRAPOLATION OF THE ASCAT-B DATA AND THE PARTIALLY EXPOSED LLCC IN SHORTWAVE IR IMAGERY. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED NEAR 28N 165E AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.0 - 25 KTS CIMSS ADT: 33 KTS AT 121140Z CIMSS AIDT: 27 KTS AT 121140Z CIMSS D-MINT: 28 KTS AT 121150Z CIMSS D-PRINT: 31 KTS AT 121140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 15-20 KTS SST: 28-29 CELSIUS OUTFLOW: WEAK EQUATORWARD OTHER FACTORS: EXTENSIVE DRY AIR ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TD 28W WILL CONTINUE TO TRACK GENERALLY NORTHWESTWARD ALONG THE SOUTHWESTERN FLANK OF A LOW- TO MID-LEVEL STR. SIGNIFICANT INTENSIFICATION APPEARS UNLIKELY. MARGINAL ENVIRONMENTAL CONDITIONS, CONSISTING OF EXTENSIVE DRY AIR AND MODERATE VWS, WILL PERSIST AND LIMIT FURTHER DEVELOPMENT. CONCURRENTLY, THE TUTT WILL PASS OVER THE SYSTEM DURING THE NEXT 12-24 HOURS. THIS MAY SUPPRESS VERTICAL MOTION AND LIMIT UPPER-LEVEL OUTFLOW. IF THE SYSTEM PERSISTS PAST TAU 36, THE SHALLOW VORTEX WILL APPROACH A SHEAR LINE ORIENTED FROM THE SOUTHWEST TO THE NORTHEAST. THIS FEATURE WILL DISRUPT THE LOW-LEVEL CIRCULATION, CAUSING TD 28W TO DEGENERATE INTO A TROUGH. THE SYSTEM COULD DISSIPATE BEFORE TAU 48. MODEL DISCUSSION: TRACK GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT, WITH THE CROSS-TRACK SPREAD DECREASING FROM 65 NM LAST CYCLE TO 30 NM THIS CYCLE AT TAU 24. THE ALONG-TRACK SPREAD IS ALSO LOW. BOTH THE DYNAMICAL AND AI MODELS ARE CLUSTERED WITHIN THE TIGHT GUIDANCE ENVELOPE. THE JTWC FORECAST TRACK IS POSITIONED WITH HIGH CONFIDENCE ALONG THE NORTHERN SIDE OF THE ENVELOPE, ALIGNING WITH THE DEEPMIND, ECMWF, AND GFS SOLUTIONS. MODEST SPREAD EXISTS AMONG THE INTENSITY AIDS. COAMPS-TC DEPICTS ADDITIONAL INTENSIFICATION TO 35 KTS BY TAU 12, FOLLOWED BY A SLOW WEAKENING TREND. DEEPMIND, HAFS-A, AND GFS HOLD THE INTENSITY THROUGH TAU 12, FOLLOWED BY GRADUAL WEAKENING. THE JTWC INTENSITY FORECAST REFLECTS THE LATTER SCENARIO WITH HIGH CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH INTENSITY 00-7…