Tropical Storm CHABA Advisory 29 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (CHABA)
WARNING NR 04//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 21W (CHABA), LOCATED APPROXIMATELY 67 NM
NORTHWEST OF ANDERSEN AFB, HAS TRACKED WESTWARD AT 11 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
DEPICTS FLARING CONVECTION ASSOCIATED WITH TD CHABA, WITH A 281704Z
AMSU 89GHZ MICROWAVE IMAGE SHOWING THE DEEPEST CONVECTIVE CELLS
DISPLACED TO THE SOUTHEAST OF THE LOW-LEVEL CIRCULATION CENTER
(LLCC). THIS ASYMMETRIC STRUCTURE IS ALSO EVIDENT IN THE RADAR
REFLECTIVITY FROM ANDERSEN AFB. THE CURRENT POSITION IS PLACED WITH
FAIR CONFIDENCE BY AID OF THE AFOREMENTIONED IMAGERY. DVORAK
INTENSITY ESTIMATES RANGE FROM T2.5 TO T3.0 FROM ALL AGENCIES, WHICH
APPEARS TO BE TOO HIGH BASED ON OTHER OBSERVATIONAL DATA. THE
CURRENT INTENSITY IS MAINTAINED AT 30 KNOTS BASED ON THE EARLIER
281128Z PARTIAL ASCAT PASS AND THE STEADY-STATE NATURE OF THE
FLARING CONVECTION SINCE THAT TIME. TD CHABA IS LOCATED IN A
MARGINAL ENVIRONMENT WITH WARM SSTS AND LOW VERTICAL WIND SHEAR, BUT
UNDER RESTRICTED POLEWARD OUTFLOW DUE TO A TUTT CELL TO THE
NORTHEAST. TD CHABA IS TRACKING WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF A DEEP LAYERED SUB-TROPICAL RIDGE (STR) TO THE
NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. THE STR WILL CONTINUE TO STEER TD CHABA TOWARD THE WEST-
NORTHWEST WITH A GRADUAL TURN TOWARD THE NORTHWEST. SLOW
INTENSIFICATION IS FORECAST IN THE NEAR TERM, FOLLOWED BY MORE
STEADY INTENSIFICATION BEYOND TAU 24 WHEN THE TUTT CELL CURRENTLY TO
THE NORTHEAST OF TD CHABA SLIDES WESTWARD AND OPENS UP A POLEWARD
OUTFLOW CHANNEL IN ITS WAKE. WITH CONTINUED LOW VERTICAL WIND SHEAR
AND IMPROVED OUTFLOW, TD CHABA IS FORECAST TO REACH TYPHOON
INTENSITY IN THE 48 TO 72 HOUR TIME FRAME. DYNAMIC MODEL GUIDANCE
REMAINS IN GOOD AGREEMENT WITH A GENERAL WEST-NORTHWEST TO
NORTHWESTWARD TRACK THROUGH TAU 72, AND THE OFFICIAL JTWC FORECAST
TRACK IS PLACED NEAR THE MULTIMODEL CONSENSUS.
   C. IN THE EXTENDED PERIOD, DYNAMIC MODEL GUIDANCE DIVERGES
GREATLY BEYOND TAU 72, WITH THE GFS AND GFS/JGSM ENSEMBLES AT THE
RIGHT SIDE OF THE MODEL GUIDANCE ENVELOPE. SINCE THE LAST WARNING,
THE EGRR HAS SHIFTED TO THE WEST OF OKINAWA, WHEREAS THE ECMWF HAS
SHIFTED TO THE EAST. DIFFERENCES IN MODEL SOLUTIONS ARE DUE TO
DIFFERENCES IN THE FORECAST INTENSITY OF THE STR. THE OFFICIAL JTWC
FORECAST TRACK REMAINS CLOSE TO THE PREVIOUS WARNING, STAYING TO THE
LEFT OF THE MULTIMODEL CONSENSUS BEYOND TAU 72. HOWEVER, THIS MAY
NEED TO BE ADJUSTED DEPENDING ON THE EVOLUTION OF FUTURE MODEL
GUIDANCE. VERTICAL WIND SHEAR IS FORECAST TO REMAIN LOW WITH GOOD
OUTFLOW, BUT THE PRESENCE OF COOLER SSTS IN THE REGION BETWEEN
OKINAWA AND TAIWAN WILL COMPLICATE THE LONG-RANGE INTENSITY
FORECAST. THE OFFICIAL INTENSITY FORECAST LIES CLOSE TO THE
INTENSITY CONSENSUS, BUT THIS IS A CASE WHERE THE ACTUAL
INTENSIFICATION RATE OF TD CHABA WILL STRONGLY DEPEND ON ITS
EVENTUAL TRACK. THIS UNCERTAINTY LEADS TO A LOW CONFIDENCE IN BOTH
THE JTWC TRACK AND INTENSITY FORECASTS BEYOND TAU 72.//
NNNN
NNNN