WDPN31 PGTW 052100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (OMAIS) WARNING NR
06//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 07W (OMAIS), LOCATED APPROXIMATELY 808 NM SOUTH-
SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 14 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS DEEP CONVECTION BEGINNING TO WRAP MORE SYMMETRICALLY
AROUND THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 051849Z SSMIS
91GHZ MICROWAVE IMAGE DEPICTS DEEP CONVECTION PERSISTING TO THE
NORTHEAST AND SOUTHEAST WITH CONVECTIVE CELLS DEVELOPING NEAR THE
LLCC. DESPITE THE LARGE WIND FIELD, THE CONVECTIVE STRUCTURE OF 07W
HAS BECOME MORE LIKE A TRADITIONAL TROPICAL CYCLONE, SO DVORAK
INTENSITY ESTIMATES HAVE INCREASED TO T3.5 FROM PGTW AND KNES. THE
CURRENT INTENSITY IS SUBSEQUENTLY ASSESSED AT 55 KNOTS. BOTH THE
INFRARED AND MICROWAVE REPRESENTATION SUGGEST THAT 07W CONTINUES TO
GRADUALLY INTENSIFY AS A LARGE TROPICAL CYCLONE WITH A BROAD WIND
FIELD, WITH THE RADIUS OF GALE-FORCE WINDS MAXIMIZING TO THE EAST OF
THE CIRCULATION. CONFIDENCE IN THE CURRENT POSITION HAS INCREASED
GIVEN THE MORE SYMMETRIC REPRESENTATION IN SATELLITE IMAGERY.
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE WITH LOW VERTICAL WIND
SHEAR AND EXCELLENT RADIAL OUTFLOW EXCEPT IN THE NORTHWEST QUADRANT,
WHERE OUTFLOW IS SOMEWHAT RESTRICTED DUE TO THE PRESENCE OF A WEAK
UPPER-TROPOSPHERIC TROUGH. TS 07W IS TRACKING POLEWARD ALONG THE
WESTERN PERIPHERY OF THE NEAR-EQUATORIAL RIDGE (NER) POSITIONED TO
THE EAST AND SOUTHEAST.
3. FORECAST REASONING.
A. NO CHANGES TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TS 07W IS FORECAST TO TRACK POLEWARD ALONG THE WESTERN
PERIPHERY OF THE NER THROUGH TAU 24 TO 36, AFTER WHICH THE STEERING
INFLUENCE WILL TRANSITION TO THAT OF THE SUBTROPICAL RIDGE (STR). A
SLIGHT TURN TO THE NORTH-NORTHWEST IS EXPECTED AS THE STR BRIEFLY
BUILDS TO THE EAST OF 07W. DYNAMIC MODEL GUIDANCE IS IN TIGHT
AGREEMENT THROUGH TAU 72. TS 07W IS FORECAST TO INTENSIFY TO A PEAK
INTENSITY OF 75 KNOTS BY TAU 36 UNDER FAVORABLE ENVIRONMENTAL
CONDITIONS. IT SHOULD MAINTAIN THIS INTENSITY UNTIL IT ROUNDS THE
STR AXIS BEFORE TAU 72. LIMITING FACTORS THAT MAY INHIBIT MORE RAPID
INTENSIFICATION ARE THE LARGE SIZE OF THE CIRCULATION AS WELL AS THE
RESTRICTED OUTFLOW TO THE NORTHWEST THAT IS FORECAST TO PERSIST.
GIVEN THE MORE FAVORABLE OUTFLOW TO THE EAST AND THE CORRESPONDING
ENHANCEMENT OF THE SECONDARY VERTICAL CIRCULATION ASSOCIATED WITH
07W, CONVECTION IS EXPECTED TO REMAIN MORE INTENSE TO THE EAST OF
THE VORTEX AND THE FORECAST WIND RADII ARE SUBSEQUENTLY GREATER IN
THE NORTHEAST AND SOUTHEASTERN QUADRANTS. HOWEVER, GALE-FORCE GUSTS
MAY STILL BE A POSSIBILITY ALONG PORTIONS OF THE COAST OF JAPAN
GIVEN THE TIGHT HORIZONTAL PRESSURE GRADIENT THAT MAY EXIST AS 07W
PASSES TO THE EAST.
C. IN THE EXTENDED TAUS, 07W IS FORECAST TO TRACK TOWARD A
WEAKNESS IN THE STR AND SHOULD BEGIN TO INTERACT WITH A MIDLATITUDE
SHORTWAVE TROUGH NEAR TAU 72. IT IS FORECAST TO BEGIN EXTRATROPICAL
TRANSITION AROUND TAU 96 AND COMPLETE THE TRANSITION BY TAU 120
AFTER INTERACTING WITH A BAROCLINIC ZONE NORTHEAST OF JAPAN AT THAT
TIME. OVERALL, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK
DUE TO IMPROVED CONFIDENCE IN THE CURRENT POSITION AND THE TIGHT
AGREEMENT OF DYNAMIC GUIDANCE.//
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