Tropical Storm ATSANI Advisory 10月31日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI)
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 232 NM
NORTHEAST OF YAP, HAS TRACKED WEST-NORTHWESTWARD AT 15 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A VERY DISORGANIZED AND WEAK SYSTEM, WITH MODERATE
DISORGANIZED FLARING CONVECTION NEAR THE ASSESSED LOW LEVEL
CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS BASED ON THE
LOW LEVEL CIRCULATION FEATURES PRESENT IN THE EIR LOOP AND IS
PLACED WITH OVERALL POOR CONFIDENCE DUE TO THE LACK OF CONVECTIVE
ORGANIZATION. THE INITIAL INTENSITY OF 30 KTS IS PLACED WITH FAIR
CONFIDENCE BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES
OF T2.0 (30 KTS, PGTW AND RJTD) AND IS SLIGHTLY BELOW AN ADVANCED
DVORAK TECHNIQUE CURRENT INTENSITY ESTIMATE OF T2.5 (35 KTS). THE
OVERALL ENVIRONMENT IS MARGINAL FOR FURTHER DEVELOPMENT WITH HIGH
(20-25 KTS) VERTICAL WIND SHEAR AND WEAK OUTFLOW ALOFT OFFSET
SLIGHTLY BY FAVORABLE (30-31 CELSIUS) SEA SURFACE TEMPERATURES (SST).
TD ATSANI IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE OVERALL FORECAST
PHILOSOPHY.
   B. TD 23W IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD THROUGH
TAU 72 ALONG THE SOUTHWESTERN EDGE OF THE STR TO THE NORTHEAST. THE
ENVIRONMENT IS FORECAST TO REMAIN MARGINAL AS WARM (29-30 CELSIUS)
SST ARE OFFSET BY CONTINUED MODERATE TO HIGH (15-25 KTS) VWS AND
PERIODS OF CONVERGENT FLOW ALOFT. THIS MARGINAL ENVIRONMENT WILL
ALLOW FOR ONLY GRADUAL INTENSIFICATION DURING THIS TIME AND RESULT
IN AN INTENSITY OF 70 KTS BY TAU 72. THERE IS A HIGH DEGREE OF
UNCERTAINTY IN THE INTENSITY FORECAST DUE TO THE TIMING OF AN
INCOMING UPPER LEVEL TROUGH FROM THE NORTHWEST THAT WILL RESULT IN
AN EROSION AND SUBSEQUENT REPOSITIONING OF THE STEERING RIDGE. THIS
REORIENTATION MAY ALLOW FOR THE ESTABLISHMENT OF A POLEWARD OUTFLOW
CHANNEL THAT IS CURRENTLY NOT REFLECTED IN THE MODEL GUIDANCE, AND
WOULD ALLOW FOR POSSIBLE RAPID INTENSIFICATION DURING THIS TIME.
NUMERICAL MODEL TRACK GUIDANCE ALSO DIVERGES SIGNIFICANTLY WITH A
SPREAD IN ACROSS TRACK MODEL SOLUTIONS OF 301 NM AT TAU 72.
SPECIFICALLY, THE NAVGEM TRACK SOLUTION LIES SIGNIFICANTLY NORTHWARD
OF THE OTHER JTWC MULTI-MODEL CONSENSUS MEMBERS. THIS SPREAD IN
SOLUTIONS LENDS OVERALL FAIR CONFIDENCE IN THIS INITIAL PORTION OF
THE JTWC FORECAST, WHICH IS PLACED SLIGHTLY SOUTH OF THE MULTI-MODEL
CONSENSUS TO OFFSET THE NORTHWARD BIAS DUE TO THE NAVGEM TRACK.
   C. IN THE EXTENDED FORECAST, THE REORIENTATION OF THE STEERING
RIDGE DUE TO THE AFOREMENTIONED INCOMING UPPER LEVEL TROUGH WILL LEAD
TO A WESTWARD AND THEN SOUTHWESTWARD TRACK. ENVIRONMENTAL CONDITIONS
ARE FORECAST TO IMPROVE DURING THIS TIME WITH VWS DECREASING TO 5-10
KTS BY TAU 120. THIS DECREASED VWS, COUPLED WITH CONTINUED WARM SST,
WILL ALLOW FOR FURTHER, GRADUAL INTENSIFICATION TO 90 KTS BY TAU 96,
WHICH THE SYSTEM WILL MAINTAIN THROUGH THE REMAINDER OF THE FORECAST
PERIOD. NUMERICAL MODEL TRACK GUIDANCE IS IN OVERALL POOR AGREEMENT
DURING THIS TIME, LARGELY DUE TO THE EXTREME NORTHWARD BIAS OF THE
NAVGEM TRACK. THE 545 NM SPREAD IN SOLUTIONS AT TAU 120 DECREASES TO
315 NM WHEN REMOVING THE NAVGEM TRACK FROM THE TRACK GUIDANCE. THIS
SPREAD IN TRACK GUIDANCE LENDS OVERALL FAIR CONFIDENCE IN THE
REMAINDER OF THE JTWC FORECAST TRACK WHICH IS PLACED SLIGHTLY SOUTH
OF THE MULTI-MODEL CONSENSUS TO OFFSET THE NORTHWARD BIAS DUE TO THE
NAVGEM TRACK.//
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