Tropical Storm FRANCISCO Advisory Wed Oct 16

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (TWENTYSIX)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 26W (TWENTYSIX), LOCATED APPROXIMATELY 55 NM
SOUTHEAST OF NAVSTA GUAM, HAS TRACKED WEST-SOUTHWESTWARD AT 13 KNOTS
OVER THE PAST SIX HOURS. RECENT ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH IMPROVED CENTRALIZED DEEP CONVECTION. A 152330Z AMSU-B
MICROWAVE IMAGE REVEALS DEEPENING CONVECTION AND AN IMPROVED CURVED
BANDING FEATURE ACROSS THE SOUTHERN SEMI-CIRCLE. THE INITIAL
POSITION IS BASED ON THE MSI ANIMATION AND RADAR FROM GUAM WITH LOW
CONFIDENCE AS THE SYSTEM IS CONTINUING TO CONSOLIDATE AND MULTIPLE
CIRCULATIONS MAY BE PRESENT. A 160023Z ASCAT PASS INDICATES A
SLIGHTLY ELONGATED LLCC WITH 25 TO 30 KNOT WIND BARBS SURROUNDING
THE CENTER, JUST TO THE SOUTHEAST OF GUAM. THIS IS CONSISTENT WITH
THE INITIAL FORECAST INTENSITY, WHICH IS ASSESSED AT 25 KNOTS BASED
ON CONGRUENT DVORAK ESTIMATES FROM RJTD AND PGTW. UPPER-LEVEL
ANALYSIS INDICATES THE SYSTEM IS IN A REGION CHARACTERIZED BY WEAK
TO MODERATE (10 TO 20 KNOTS) VERTICAL WIND SHEAR (VWS) AND STRONG
UPPER-LEVEL DIVERGENCE. TD 26W IS POSITIONED WELL SOUTH OF ANY
SUBTROPICAL RIDGE (STR) AND CURRENTLY TRACKING WITH THE BACKGROUND
ENVIRONMENTAL FLOW TO THE SOUTHWEST.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 26W IS EXPECTED TO CONTINUE DEVELOPING AND TRACK SOUTHWEST
WITH THE BACKGROUND ENVIRONMENTAL FLOW FOR THE NEXT 12 HOURS. AFTER
TAU 12, AN EXTENSION OF THE STR WILL BEGIN TO BUILD-IN STEERING THE
SYSTEM WESTWARD THROUGH TAU 24 AND EVENTUALLY EVEN MORE POLEWARD IN
A NORTH-NORTHWEST DIRECTION THROUGH TAU 48. FAVORABLE SEA SURFACE
TEMPERATURES AND LOW VWS ALONG THE TRACK WILL ALLOW THE SYSTEM TO
GRADUALLY INTENSIFY, WITH THE POTENTIAL FOR RAPID INTENSIFICATION,
TO 60 KNOTS BY TAU 48. THE SUBTROPICAL STEERING RIDGE WILL BEGIN TO
BUILD-IN AFTER TAU 48 AND DIRECT TD 26W TO THE NORTHWEST AS IT
TRACKS AROUND THE SOUTHWEST PERIPHERY OF THE DEVELOPING STR. THE
SYSTEM WILL REMAIN ON THIS TRACK THROUGH TAU 72 WITH CONTINUED
FAVORABLE ENVIRONMENTAL CONDITIONS ALLOWING TD 26W TO REACH AN
INTENSITY OF 80 KNOTS. THOUGH THE OBJECTIVE AIDS ARE GROUPED FAIRLY
TIGHTLY, THE CONFIDENCE THROUGH THIS PORTION OF THE FORECAST IS
INITIALLY LOW DUE TO THE SLIGHT DISORGANIZATION OF THE SYSTEM AND
THE GENERALLY WEAK STEERING CONDITIONS.
   C. TD 26W IS FORECAST TO CONTINUE TRACKING ALONG THE SOUTHWEST
PERIPHERY OF THE SUBTROPICAL STEERING RIDGE THROUGH TAU 120.
CONTINUED FAVORABLE SSTS, LOW VWS AND THE POTENTIAL FOR DUAL CHANNEL
OUTFLOW WILL ALLOW FOR INTENSIFICATION TO 105 KNOTS BY TAU 120.
THERE IS GENERALLY GOOD AGREEMENT AMONG THE OBJECTIVE AIDS THROUGH
TAU 120, WITH ONLY SLIGHT DIFFERENCES IN TRACK SPEED AND POSITION.
DESPITE THIS, THERE IS OVERALL LOW CONFIDENCE IN THE FORECAST TRACK
DUE TO THE CURRENT DISORGANIZATION OF THE LLCC AND THE POORLY
DEFINED STEERING CONDITIONS.//
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