(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 6.4S 76.4E,
IS NOW LOCATED NEAR 8.7S 72.3E, APPROXIMATELY 75 NM SOUTH-SOUTHWEST
OF DIEGO GARCIA. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A
DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) WITH DEVELOPING CENTRAL
CONVECTION NOW EVIDENT. A 131348Z SSMIS 91GHZ MICROWAVE IMAGE SHOWS
AN IMPROVED LLCC WITH CONVECTION ALONG THE SOUTHERN AND WESTERN
PORTION OF THE LLCC. OBSERVATIONS FROM DIEGO GARCIA SHOW DECREASING
PRESSURE OVER THE PAST 24 HOURS AS THE DISTURBANCE PASSED TO THE
SOUTH. UPPER LEVEL ANALYSIS SHOWS AN IMPROVED ENVIRONMENT WITH
DECREASING VERTICAL WIND SHEAR (10-15 KNOTS) AND GOOD DIVERGENCE
WITH AN ENHANCED POLEWARD OUTFLOW CHANNEL, EVIDENT ON WATER VAPOR
IMAGERY. SEA SURFACE TEMPERATURES ARE FAVORABLE NEAR 28 CELSIUS.
GLOBAL MODELS REMAIN MIXED WITH GFS THE MOST AGGRESSIVE SHOWING
STRONGER GRADIENT WINDS WRAPPING AROUND THE LLCC AS IT TRACKS
SOUTHWESTWARD TOWARDS MADAGASCAR. MAXIMUM SUSTAINED SURFACE WINDS
ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 1005 MB. DUE TO THE LLCC CONSOLIDATION AND
IMPROVED UPPER LEVEL ENVIRONMENT, THE POTENTIAL FOR THE DEVELOPMENT
OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS
UPGRADED TO MEDIUM.
WTXS21 PGTW 151600
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
A 210 NM RADIUS OF 8.5S 69.0E WITHIN THE NEXT 12 TO 24 HOURS.
AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL
CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO
BE 25 TO 30 KNOTS. METSAT IMAGERY AT 151200Z INDICATES THAT A
CIRCULATION CENTER IS LOCATED NEAR 8.5S 69.0E. THE SYSTEM IS
MOVING NORTHEASTWARD AT 08 KNOTS.
2. REMARKS: ANIMATED INFRARED SATELLITE IMAGERY AND A 151322Z SSMIS
91GHZ IMAGE REVEAL PERSISTENT DEEP CONVECTION AND SHALLOW BANDING
WRAPPING INTO THE LLCC. PREVIOUS ASCAT IMAGERY SHOWS 25 TO 30 KNOTS
OF WIND ON THE SOUTHWEST QUADRANT WRAPPING INTO THE SYSTEM. A RECENT
OBSERVATION ALSO SHOWS 30 KNOT WINDS APPROXIMATELY 250 NM SOUTHEAST
OF THE SYSTEM. ENVIRONMENTAL CONDITIONS HAVE IMPROVED
SLIGHTLY OVER THE PAST 24 HOURS WITH VERTICAL WIND SHEAR RELAXING
OVER THE CIRCULATION CENTER BUT STILL RELATIVELY HIGH TO THE NORTH
AND GOOD DIVERGENT OUTFLOW. SEA SURFACE TEMPERATURES ARE ALSO
FAVORABLE FOR DEVELOPMENT NEAR 28 CELSIUS. CURRENTLY THERE IS NO
DOMINANT STEERING MECHANISM AS A LONG WAVE TROUGH TO THE SOUTH HAS
SUFFICIENTLY WEAKENED THE SUBTROPICAL RIDGE (STR) PREVIOUSLY TAKING
THE DISTURBANCE ON A SOUTHWEST TRACK. GLOBAL MODELS ARE IN GOOD
AGREEMENT THAT THE DEEP-LAYERED STR WILL REESTABLISH ITSELF BY TAU
24 TO 36 STEERING THE SYSTEM ON A SOUTHWESTERN TRACK.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY
161600Z.
//
(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 5.6S 77.6E,
IS NOW LOCATED NEAR 6.4S 76.4E, APPROXIMATELY 250 NM EAST-NORTHEAST
OF DIEGO GARCIA. ANIMATED INFRARED SATELLITE IMAGERY AND A 121344Z
SSMIS 91GHZ MICROWAVE IMAGE DEPICT A BROAD AND ELONGATED LOW LEVEL
CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION IN THE
SOUTHWESTERN PERIPHERY. A PREVIOUS METOP-A 120451Z ASCAT PASS
DEPICTED WINDS OF 5-10 KNOTS ASSOCIATED WITH THE LLCC. THE CURRENT
UPPER LEVEL ENVIRONMENT IS RATHER HOSTILE, WITH HIGH VERTICAL WIND
SHEAR OF 30-50 KNOTS IN THE VICINITY, SO CONVECTIVE ORGANIZATION IS
NOT EXPECTED TO IMPROVE IN THE NEAR TERM. HOWEVER, GLOBAL MODELS
SUGGEST THE POSSIBILITY OF SOME MODEST DEVELOPMENT OF THE
DISTURBANCE AS IT TRACKS WEST-SOUTHWESTWARD, IN RESPONSE TO
SOUTHEASTERLY WINDS AT THE SURFACE THAT INDUCE A SURFACE VORTICITY
RESPONSE. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 10 TO 15
KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1007 MB.
THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE
WITHIN THE NEXT 24 HOURS REMAINS LOW.
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