
WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (NORU) WARNING NR 61//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON 07W (NORU), LOCATED APPROXIMATELY 213 NM NORTHEAST OF
KADENA AB, HAS TRACKED NORTHWESTWARD AT 03 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY AND RADAR
IMAGERY INDICATE THAT TY 07W IS CONTINUING TO RE-INTENSIFY.
CONVECTIVE STRUCTURE IS GRADUALLY IMPROVING, AND THE ONCE-RAGGED
EYE IS BEGINNING TO CONSOLIDATE WITH GREATER SYMMETRY AND TIGHTER
HORIZONTAL BRIGHTNESS TEMPERATURE GRADIENT IN THE INNER EYEWALL. A
041751Z SSMI 85GHZ MICROWAVE IMAGE DEPICTS THE MOST INTENSE
CONVECTION IN THE SOUTHEASTERN QUADRANT OF THE SYSTEM WRAPPING
AROUND A LARGE MICROWAVE EYE WITH AN EASTERN RADIUS OF
APPROXIMATELY 30 NM. THE INITIAL POSITION IS PLACED WITH GOOD
CONFIDENCE, WITH THE CENTER OF THE EYE CLEARLY DEPICTED IN JMA
RADAR WITH SOME MESOSCALE VORTICES ROTATING AROUND THE INNER
PERIPHERY OF THE EYEWALL. THE INITIAL INTENSITY IS SET AT 80 KNOTS
BASED ON MULTI-AGENCY DVORAK ESTIMATES OF T4.5 AND THE CURRENT
TREND OF IMPROVEMENT IN CONVECTIVE STRUCTURE. YAKUSHIMA,
APPROXIMATELY 70 NM TO THE NORTH OF THE CENTER, HAS OBSERVED
STEADILY INCREASING WINDS TO 35 KNOTS SUSTAINED WITH GUSTS TO 59
KNOTS, WITH CORRESPONDING PRESSURE FALLS OF ABOUT 1 MB PER HOUR. TY
07W HAS SLOWED ITS FORWARD MOTION AS DEEP-LAYER STEERING BEGINS TO
WEAKEN AROUND THE SOUTHWEST PERIPHERY OF THE SUBTROPICAL RIDGE
(STR).
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST TRACK PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, BUT THE PEAK INTENSITY FORECAST HAS
BEEN INCREASED TO 100 KNOTS AT TAU 24 TO CAPTURE THE INCREASINGLY
FAVORABLE ENVIRONMENTAL CONDITIONS THAT ARE SUPPORTING THE CURRENT
RE-INTENSIFICATION PHASE.
B. TY 07W IS FORECAST TO INTENSIFY TO 100 KNOTS OVER THE NEXT
24 HOURS AS IT RECURVES TO THE NORTH, WITH IMPROVING POLEWARD
OUTFLOW AHEAD OF AN APPROACHING MID-LATITUDE SHORTWAVE TROUGH.
VERTICAL WIND SHEAR IS FORECAST TO DECREASE OVER THE SYSTEM IN THE
NEAR TERM AS THE STEERING RIDGE PUSHES OFF TO THE EAST AHEAD OF THE
TROUGH, ACQUIRING A MERIDIONAL ORIENTATION AND SUBSEQUENTLY DRIVING
TY 07W NORTH-NORTHEASTWARD INTO THE SEA OF JAPAN. PRIOR TO LANDFALL
IN KYUSHU AROUND TAU 36, TY 07W WILL TRAVERSE WARM WATERS WITH SEA-
SURFACE TEMPERATURES EXCEEDING 31C AND HIGH OCEAN HEAT CONTENT.
GIVEN THE FAVORABLE UPPER-TROPOSPHERIC AND OCEANIC CONDITIONS, A
BRIEF PERIOD OF RAPID INTENSIFICATION IS A POSSIBILITY AS THE
SYSTEM MAKES ITS SLOW, POLEWARD TURN. THE GFS HAS BEEN THE MOST
AGGRESSIVE, WITH THE 12Z RUN SUGGESTING SIGNIFICANT PRESSURE FALLS
TO 908 MB BY TAU 36. HOWEVER, THIS APPEARS TO BE A CONSISTENT LOW
BIAS IN THE GFS, RELATED TO THE SYSTEM BEING AT HIGHER-LATITUDE.
THE HWRF, ECMWF AND OTHER MODELS SUGGESTING A MORE MODEST
INTENSIFICATION RATE. BUT GIVEN THE FAVORABLE ENVIRONMENTAL
CONDITIONS, THE OFFICIAL FORECAST IS INCREASED SLIGHTLY FROM THE
LAST WARNING CYCLE TO CAPTURE THE POSSIBILITY OF MORE RAPID
INTENSIFICATION. AFTER THIS PERIOD OF INTENSIFICATION IS COMPLETE,
INCREASING VERTICAL WIND SHEAR ASSOCIATED WITH THE SHORTWAVE TROUGH
ALONG WITH LAND INTERACTION WITH SOUTHERN JAPAN WILL WEAKEN THE
SYSTEM.
C. AFTER TAU 72, TY 07W IS FORECAST TO TRACK NORTH-
NORTHEASTWARD, STEERED BY THE MERIDIONALLY-ORIENTED SUBTROPICAL
RIDGE AXIS TO THE EAST OF JAPAN. THE MID-LATITUDE SHORTWAVE TROUGH
IS FORECAST TO AMPLIFY OVER THE KOREAN PENINSULA, WITH THE RIGHT-
ENTRANCE REGION OF AN INTENSIFYING JET STREAK SITUATED ALONG AND
AHEAD OF THE FORECAST TRACK OF TY 07W. BAROCLINIC DYNAMICS,
INCLUDING AGEOSTROPHIC JET STREAK FORCING, WILL INITIATE EXTRA-
TROPICAL TRANSITION (ETT) OF THE SYSTEM. TY 07W IS FORECAST TO
COMPLETE ETT BY TAU 96. NUMERICAL MODEL GUIDANCE IS IN GOOD
AGREEMENT WITH THE FORECAST TRACK, BUT GIVEN THE RECENT DECREASE IN
FORWARD MOTION IN RESPONSE TO WEAKER ENVIRONMENTAL STEERING FLOW,
THE FORECAST TRACK IS PLACED JUST SLIGHTLY BEHIND THE MULTI-MODEL
CONSENSUS. OVERALL, THERE IS GOOD CONFIDENCE IN THE JTWC FORECAST
TRACK.//
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