Tropical Storm PHANFONE Advisory Mon Sep 29

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY
305 NM NORTH-NORTHEAST OF CHUUK, HAS TRACKED WEST-NORTHWESTWARD AT
18 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE (EIR) IMAGERY DEPICTS BROAD CONVECTION WITH AN ILL-DEFINED
LOW-LEVEL CIRCULATION CENTER (LLCC). A 281818Z SSMIS AND 281450Z
AMSR2 IMAGE REVEAL FORMATIVE BROAD BANDING AROUND THE LLCC, HOWEVER,
THE SYSTEM IS STILL IN ITS INFANCY AND NOT WELL CONSOLIDATED. THIS
LEADS TO A LOW CONFIDENCE IN ITS INITIAL POSITION. THE INITIAL
INTENSITY IS ASSESSED AT 25 KNOTS BASED ON AN AVERAGE OF THE DVORAK
CURRENT INTENSITY ESTIMATES FROM ALL AGENCIES. THERE IS A FAVORABLE
UPPER-LEVEL ENVIRONMENT DUE TO LOW (5 TO 10 KNOTS) OF VERTICAL WIND
SHEAR (VWS) AND GOOD POLEWARD PROVIDED BY A TUTT TO THE NORTHEAST OF
THE SYSTEM AND EQUATORWARD OUTFLOW. TD 18W IS TRACKING TO THE
NORTHEAST ALONG THE SOUTHERN PERIPHERY OF THE DOMINANT SUBTROPICAL
RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 18W WILL CONTINUE TO TRACK ALONG THE SOUTHWESTERN EDGE OF
THE STR THROUGH THE NEXT 72 HOURS. MODELS ARE IN GOOD AGREEMENT WITH
THE SYSTEM TRACKING TO THE NORTHEAST OVER THE NEXT 48 HOURS THROUGH
THE NORTHERN PORTION OF THE MARIANA ISLANDS. ADDITIONALLY, EXPECT
THE UPPER-LEVEL ENVIRONMENT TO IMPROVE AS A SMALL TUTT CELL TO THE
NORTHWEST OF THE SYSTEM DISSIPATES, LIMITING THE VWS, AND THE
NORTHEASTERN TUTT CONTINUES TO PROVIDE A GOOD POLEWARD OUTFLOW
CHANNEL. ADDITIONALLY, LARGE OCEAN HEAT ENERGY CONTENT COMBINED WITH
THE AFOREMENTIONED ENHANCING UPPER-LEVEL ENVIRONMENT MAY POTENTIALLY
ALLOW TD 18W TO BECOME TYPHOON STRENGTH BY TAU 72. THE SPREAD IN THE
MODELS BECOME MORE SIGNIFICANT NEAR TAU 72, WITH A DISPARITY OF
ABOUT 250NM.
   C. IN THE EXTENDED FORECAST, THERE IS MODERATE DISAGREEMENT IN
MODELS WITH REGARD TO THE STRENGTH OF THE STR AND WHERE TD 18W
BEGINS TO TURN INTO THE BREAK IN THE RIDGE, OR EVEN IF A BREAK
DEVELOPS. HWRF IS THE WESTERN, MORE FLAT OUTLIER WHILE GFDN AND
COAMPS-TC (BOTH NAVGEM AND GFS) DEPICT THE EASTERN, MORE NORTHERN
SCENARIO. DUE TO THE SPREAD OF OVER 450NM IN BY TAU 120, THE JTWC
TRACK CLOSELY RESEMBLES THE MULTI-MODEL CONSENSUS WITH OVERALL LOW
CONFIDENCE IN THE FORECAST TRACK.//
NNNN
NNNN