1. TROPICAL CYCLONE 17P (IRIS) WARNING NR 020
01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
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WARNING POSITION:
040000Z --- NEAR 19.3S 150.4E
MOVEMENT PAST SIX HOURS - 150 DEGREES AT 04 KTS
POSITION ACCURATE TO WITHIN 040 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 050 KT WINDS - 055 NM NORTHEAST QUADRANT
065 NM SOUTHEAST QUADRANT
050 NM SOUTHWEST QUADRANT
040 NM NORTHWEST QUADRANT
RADIUS OF 034 KT WINDS - 110 NM NORTHEAST QUADRANT
155 NM SOUTHEAST QUADRANT
130 NM SOUTHWEST QUADRANT
090 NM NORTHWEST QUADRANT
REPEAT POSIT: 19.3S 150.4E
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FORECASTS:
12 HRS, VALID AT:
041200Z --- 19.6S 150.8E
MAX SUSTAINED WINDS - 050 KT, GUSTS 065 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 050 KT WINDS - 035 NM NORTHEAST QUADRANT
035 NM SOUTHEAST QUADRANT
045 NM SOUTHWEST QUADRANT
040 NM NORTHWEST QUADRANT
RADIUS OF 034 KT WINDS - 115 NM NORTHEAST QUADRANT
135 NM SOUTHEAST QUADRANT
135 NM SOUTHWEST QUADRANT
095 NM NORTHWEST QUADRANT
VECTOR TO 24 HR POSIT: 090 DEG/ 01 KTS
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24 HRS, VALID AT:
050000Z --- 19.6S 151.0E
MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT
140 NM SOUTHEAST QUADRANT
140 NM SOUTHWEST QUADRANT
075 NM NORTHWEST QUADRANT
VECTOR TO 36 HR POSIT: 155 DEG/ 01 KTS
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36 HRS, VALID AT:
051200Z --- 19.8S 151.1E
MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 075 NM NORTHEAST QUADRANT
150 NM SOUTHEAST QUADRANT
150 NM SOUTHWEST QUADRANT
080 NM NORTHWEST QUADRANT
VECTOR TO 48 HR POSIT: 270 DEG/ 01 KTS
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EXTENDED OUTLOOK:
48 HRS, VALID AT:
060000Z --- 19.8S 150.9E
MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 065 NM NORTHEAST QUADRANT
135 NM SOUTHEAST QUADRANT
105 NM SOUTHWEST QUADRANT
060 NM NORTHWEST QUADRANT
VECTOR TO 72 HR POSIT: 310 DEG/ 01 KTS
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72 HRS, VALID AT:
070000Z --- 19.5S 150.5E
MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT
115 NM SOUTHEAST QUADRANT
080 NM SOUTHWEST QUADRANT
030 NM NORTHWEST QUADRANT
VECTOR TO 96 HR POSIT: 300 DEG/ 02 KTS
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LONG RANGE OUTLOOK:
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96 HRS, VALID AT:
080000Z --- 19.2S 149.9E
MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
---
REMARKS:
040300Z POSITION NEAR 19.4S 150.5E.
TROPICAL CYCLONE 17P (IRIS), LOCATED APPROXIMATELY 299 NM EAST-
SOUTHEAST OF CAIRNS, AUSTRALIA, HAS TRACKED SOUTH-SOUTHEASTWARD
AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY SHOWS DIMINISHING CONVECTIVE BANDING WRAPPING INTO
THE CENTER, PARTIALLY COVERING THE LOW LEVEL CIRCULATION CENTER
(LLCC). THE INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE BASED ON
THE MSI LOOP AND 00Z PGTW FIX, SUPPORTED BY A 032010Z SSMIS 37GHZ
MICROWAVE IMAGE SHOWING A PARTIALLY CLOSED LOW REFLECTIVITY DIMPLE
AT THE CENTER. THE INITIAL INTENSITY IS BASED ON A 032249Z ASCAT
PASS REVEALING SEVERAL 50 KT WINDS BARBS CLOSE TO THE CENTER, AND IS
SUPPORTED BY A 46 KT SUSTAINED OBSERVATION FROM 68NM AWAY, IMPLYING
HIGHER WINDS CLOSER TO THE CENTER. THE INTENSITY AGREES WITH THE
PGTW CURRENT INTENSITY (CI) ESTIMATE OF T3.5 (55 KTS) AND IS
SLIGHTLY ABOVE THE KNES CI OF T3.0 (45 KTS). UPPER LEVEL ANALYSIS
INDICATES TC 17P IS IN AN AREA OF MODERATE TO HIGH (15-25 KT)
VERTICAL WIND SHEAR (VWS) AND THERE IS CONVERGENCE ALOFT TO THE
NORTHWEST, BOTH OF WHICH ARE SUPPRESSING CONVECTION. THESE
UNFAVORABLE INFLUENCES ARE SOMEWHAT OFFSET BY A POLEWARD OUTFLOW
CHANNEL. ALONG-TRACK SSTS REMAIN FAVORABLE AT 27C. TC 17P HAS BEGUN
TO INGEST DRY AIR FROM THE WEST, DIMINISHING ITS CONVECTIVE
SIGNATURE BUT NOT YET LEADING TO WEAKENING. TC IRIS IS TRACKING
ALONG THE SOUTHWEST PERIPHERY OF THE NEAR EQUATORIAL RIDGE EXTENSION
TO THE NORTHEAST, AND IS EXPECTED TO CONTINUE TO THE SOUTHEAST ON
THIS TRACK UNTIL TAU 36 AND GRADUALLY WEAKEN DUE TO DRY AIR
ENTRAINMENT AND INCREASING VWS. AT TAU 36, A DEEP TROUGH MOVES INTO
THE AREA FROM THE WEST, INCREASING VERTICAL WIND SHEAR FURTHER, AND
THE NEAR EQUATORIAL RIDGE TO THE NORTHEAST RECEDES, LEADING TO A
QUASISTATIONARY PERIOD. AS TC 17P DEGRADES, IT WILL BECOME SUBJECT
TO MID-LAYER AND SHALLOW STEERING FLOW FROM THE TROUGH, AND TC 17P
IS FORECAST TO MOVE TO THE NORTHWEST. AVAILABLE NUMERICAL MODEL
GUIDANCE IS SIGNIFICANTLY SPREAD AND TRIFURCATED AFTER TAU 24, WITH
COAMPS AND NAVGEM SOLUTIONS TRACKING TC 17P OVER OCEAN TO THE EAST,
MANY MODELS INCLUDING GFS AND ECMWF EXECUTING A LOOP AND MOVING TC
17P EITHER NORTH OR NORTH-NORTHEASTWARD, AND THE WESTERN OUTLIER
HWRF PREDICTING A LOOP AND THEN WESTWARD TRACK. IN LIGHT OF THIS,
THERE IS OVERALL LOW CONFIDENCE IN THE JTWC TRACK FORECAST THAT IS
LAID SLIGHTLY SLOWER AND WESTWARD OF MODEL CONSENSUS TO OFFSET THE
EASTWARD OUTLYING TRACKS. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 040000Z
IS 14 FEET. NEXT WARNINGS AT 040900Z, 041500Z, 042100Z AND 050300Z.
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