1. TROPICAL CYCLONE 17P (IRIS) WARNING NR 022
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:
041200Z --- NEAR 19.5S 151.4E
MOVEMENT PAST SIX HOURS - 120 DEGREES AT 04 KTS
POSITION ACCURATE TO WITHIN 020 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
155 NM SOUTHEAST QUADRANT
135 NM SOUTHWEST QUADRANT
115 NM NORTHWEST QUADRANT
REPEAT POSIT: 19.5S 151.4E
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FORECASTS:
12 HRS, VALID AT:
050000Z --- 19.7S 151.9E
MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 065 NM NORTHEAST QUADRANT
145 NM SOUTHEAST QUADRANT
130 NM SOUTHWEST QUADRANT
070 NM NORTHWEST QUADRANT
VECTOR TO 24 HR POSIT: 090 DEG/ 00 KTS
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24 HRS, VALID AT:
051200Z --- 19.7S 152.0E
MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 035 NM NORTHEAST QUADRANT
135 NM SOUTHEAST QUADRANT
140 NM SOUTHWEST QUADRANT
065 NM NORTHWEST QUADRANT
VECTOR TO 36 HR POSIT: 315 DEG/ 01 KTS
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36 HRS, VALID AT:
060000Z --- 19.6S 151.9E
MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 045 NM NORTHEAST QUADRANT
110 NM SOUTHEAST QUADRANT
080 NM SOUTHWEST QUADRANT
090 NM NORTHWEST QUADRANT
VECTOR TO 48 HR POSIT: 305 DEG/ 03 KTS
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EXTENDED OUTLOOK:
48 HRS, VALID AT:
061200Z --- 19.2S 151.3E
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 - 050 NM NORTHEAST QUADRANT
090 NM SOUTHEAST QUADRANT
095 NM SOUTHWEST QUADRANT
055 NM NORTHWEST QUADRANT
VECTOR TO 72 HR POSIT: 335 DEG/ 03 KTS
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72 HRS, VALID AT:
071200Z --- 18.1S 150.7E
MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
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REMARKS:
041500Z POSITION NEAR 19.6S 151.5E.
TROPICAL CYCLONE (TC) 17P (IRIS), LOCATED APPROXIMATELY 355 NM EAST-
SOUTHEAST OF CAIRNS, AUSTRALIA, HAS TRACKED EAST-SOUTHEASTWARD AT 04
KNOTS OVER THE PAST SIX HOURS. ANIMATED EIR SATELLITE IMAGERY SHOWS A
BROAD BUT PARTLY-EXPOSED LLC WITH THE CENTRAL CONVECTION NOW WEAKER
AND DISPLACED MORE SOUTHWARD. THE INITIAL POSITION IS PLACED WITH
MODERATE CONFIDENCE BASED ON EXTRAPOLATION FROM LOW CLOUD BANDS
FEEDING INTO AN OBSCURED LLCC. THE BROAD LLC AND STARKLY DISPLACED
CONVECTION ARE MATCHED IN THE 040843Z COLORIZED 91 GHZ SSMIS
MICROWAVE PASS. THE INITIAL INTENSITY IS BASED ON AN OVERALL
ASSESSMENT OF AGENCY DVORAK ESTIMATES FROM PGTW (T3.0), KNES (T2.5),
AND ABRF (T3.0) THAT ARE VALIDATED BY A 041118Z PARTIAL ASCAT PASS
SHOWING A FEW 45-KNOT WIND BARBS ALONG THE WESTERN FLANK, AND
REFLECTS THE WEAKENED STATE OF TC 17P. UPPER LEVEL ANALYSIS INDICATES
THAT THE CYCLONE IS IN AN AREA OF MODERATE (15-20 KNOT) VWS THAT IS
MOSTLY OFFSET BY AN EXCELLENT POLEWARD OUTFLOW. ALONG-TRACK SSTS AT
29C ARE ALSO CONDUCIVE. THE SYSTEM IS TRACKING SLOWLY BUT IMMINENTLY
INTO A COL ALONG THE SOUTHWESTERN PERIPHERY OF A WEAKENING NER TO THE
NORTHEAST. IRIS IS EXPECTED TO ENTER INTO A QUASI-STATIONARY (QS)
STATE IN THE COL BETWEEN THE NER AND THE STR TO THE SOUTHWEST. DURING
THIS PHASE, THE CYCLONE WILL SLOWLY RECURVE NORTHWESTWARD AS THE STR
EVENTUALLY DOMINATES AS THE PRIMARY STEERING MECHANISM. TC 17P IS
FORECAST TO GRADUALLY WEAKEN AS VWS INCREASES IN THE NEAR TERM AND IN
ADDITION, A MID-LATITUDE TROUGH APPROACHING FROM THE SOUTHWEST WILL
CAUSE SUBSIDENCE AND FURTHER ERODE THE ASSOCIATED CONVECTION.
AVAILABLE NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT
WITH THE EVENTUAL U-TURN EQUATORWARD BUT WITH NOTABLE DIFFERENCES IN
TRACK SPEED. NAVGEM IS NOW THE SOLE EASTWARD OUTLIER. IN VIEW OF
THIS, AND GIVEN THE UNCERTAINTY OF A QS STATE, THERE IS OVERALL LOW
CONFIDENCE IN THE JTWC TRACK FORECAST THAT IS LAID JUST SLIGHTLY
SLOWER AND A BIT WESTWARD OF MODEL CONSENSUS TO OFFSET THE EASTWARD
PULL OF NAVGEM. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 041200Z IS 13
FEET. NEXT WARNINGS AT 042100Z, 050300Z, 050900Z AND 051500Z.
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