Tropical Storm LEKIMA Advisory 8月9日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 10W (LEKIMA) WARNING NR 20//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 10W (LEKIMA), LOCATED APPROXIMATELY 183 NM WEST-
SOUTHWEST OF KADENA AB, HAS TRACKED NORTH-NORTHWESTWARD AT 11 KNOTS
(KTS) OVER THE PAST SIX HOURS. A 10 NM ROUND EYE IN ANIMATED
ENHANCED INFRARED SATELLITE PROVIDES HIGH CONFIDENCE IN THE INITIAL
POSITION. DESPITE THE EYE REMAINING SMALL AND ROUND, THE SURROUNDING
CONVECTION HAS BECOME ASYMMETRIC WITH SOME EROSION ON THE NORTHERN
SIDE. ADDITIONALLY, THE SIX-HOUR ANIMATION REVEALS THE EYE MADE A
TEMPORARY DEVIATION NORTHWARD BEFORE SETTLING BACK ONTO A
NORTHWESTWARD TRACK. THE INITIAL INTENSITY OF 120 KTS IS SLIGHTLY
BELOW CURRENT INTENSITY ESTIMATES FROM PGTW AND RJTD OF T6.5 (130
KTS). THE REASONS FOR HOLDING THE MAXIMUM WIND SPEED BELOW THE
DVORAK CURRENT INTENSITIES ARE LOWER FINAL T NUMBERS IN BOTH
AGENCIES DVORAK REPORTS AND MAXIMUM REPORTED SUSTAINED WINDS AT
MIYAKO-JIMA OF 45 KTS AS THE SYSTEM PASSED ABOUT 30 NM TO THE WEST
OF THE STATION. ALTHOUGH THE ENVIRONMENT HAS GOOD POLEWARD OUTFLOW,
FAIR EQUATORWARD OUTFLOW, LOW (10-15 KT) VERTICAL WIND SHEAR (VWS),
AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURE IS FAVORABLE, IT
HAS BECOME SLIGHTLY LESS FAVORABLE OVER THE PAST SIX HOURS. TY 10W
IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF A SUBTROPICAL RIDGE
(STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE. HOWEVER, THE TEMPORARY
NORTHWARD MOTION OF THE SYSTEM HAS SHIFTED THE TRACK EAST. THIS
SHIFT IS EXPECTED TO KEEP TY 10W NEAR THE COAST OF CHINA, INSTEAD OF
BRINGING IT INLAND, AND THE FORECAST HAS BEEN EXTENDED TO 120 HOURS
AGAIN.
   B. THROUGH TAU 24, TY 10W WILL CONTINUE ON ITS CURRENT
NORTHWESTWARD TRACK UNDER THE INFLUENCE OF THE STR. AFTER TAU 24,
THE TRACK WILL SHIFT MORE NORTHWARD AS THE STR REORIENTS AND RECEDES
SLIGHTLY EAST. TY 10W SHOULD MAKE LANDFALL ABOUT 140 NM SOUTH OF
SHANGHAI, CHINA. THE SYSTEM SHOULD PASS NEAR SHANGHAI ON A NORTHWARD
TRACK AROUND TAU 48 AND EMERGE OVER THE YELLOW SEA ON A NORTH-
NORTHWESTWARD TRACK PRIOR TO TAU 72. LAND INTERACTION IS EXPECTED TO
WEAKEN THE SYSTEM TO 50 KNOTS BY TAU 72; HOWEVER, THE INTENSITY
FORECAST IS VERY UNCERTAIN BECAUSE SMALL SHIFTS IN THE TRACK COULD
HAVE SIGNIFICANT IMPACT ON THE AMOUNT OF WEAKENING. NUMERICAL MODEL
TRACK GUIDANCE IS IN FAIR AGREEMENT, LENDING TO FAIR CONFIDENCE IN
THE JTWC TRACK FORECAST THROUGH TAU 72.
   C. BETWEEN TAU 72 AND 96, TY 10W WILL CONTINUE TRACKING NORTH-
NORTHWESTWARD. AFTER TAU 96, THE SYSTEM WILL ROUND THE STR AXIS AND
START TO RECURVE. HIGH VWS AND LAND INTERACTION ARE EXPECTED TO
CONTINUE WEAKENING THE SYSTEM, HOWEVER UNCERTAINTY IN THE INTENSITY
REMAINS VERY HIGH DUE TO UNCERTAINTY IN THE AMOUNT OF LAND
INTERACTION. NUMERICAL MODEL SPREAD INCREASES SIGNIFICANTLY AS
SEVERAL MODELS (ECMWF, GALWEM, UKMET) FOLLOW THE RECURVE SCENARIO
WHILE THE OTHERS SHOW THE SYSTEM DISSIPATING OVER CHINA. THE JTWC
TRACK FORECAST FAVORS THE RECURVE SCENARIO WITH LOW CONFIDENCE DUE
TO MODEL SPREAD EXCEEDING 400 NM AT TAU 120.//
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