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Tropical Storm IRWIN


ZCZC MIATCDEP1 ALL
TTAA00 KNHC DDHHMM
 
TROPICAL STORM IRWIN DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
200 PM PDT TUE OCT 11 2011
 
A BALL OF COLD-TOPPED CONVECTION HAS PERSISTED NEAR THE ESTIMATED
CENTER OF IRWIN FOR A WHILE NOW...WITH VISIBLE SATELLITE
IMAGERY INDICATING SOME INCREASE IN THE ORGANIZATION OF BANDING
FEATURES IN THE LAST FEW HOURS.  DVORAK INTENSITY ESTIMATES HAVE
INCREASED TO 35 KT AND 45 KT FROM SAB AND TAFB...RESPECTIVELY.
GIVEN THAT A 1650 UTC ASCAT OVERPASS SHOWED A FEW 35 KT WIND
VECTORS...THE INITIAL INTENSITY IS RAISED TO 40 KT.
 
EVEN THOUGH IRWIN HAS MADE A COMEBACK...ITS LONGER-TERM FUTURE IS
NOT AS PROMISING. THE REJUVENATED APPEARANCE OF IRWIN COINCIDES
WITH ITS DEPARTURE FROM A NEARBY STRATOCUMULUS FIELD AND ASSOCIATED
STABLE AIR MASS.  WITH ONLY MODERATE SHEAR FORECAST DURING THE NEXT
DAY OR SO...THERE IS SOME LIKELIHOOD OF SHORT-TERM INTENSIFICATION
AND THE INTENSITY GUIDANCE REFLECTS THIS. THE CYCLONE IS THEN
EXPECTED TO ENTER A HIGH SHEAR ENVIRONMENT DUE TO STRONG LOW-LEVEL
WESTERLY FLOW AND EASTERLIES ALOFT IN 2 TO 5 DAYS.  THIS PROLONGED
EXPOSURE TO SHEAR WILL PROBABLY CAUSE IRWIN TO WEAKEN AND THE
CYCLONE IS EXPECTED TO DEGENERATE TO A REMNANT LOW BY AROUND DAY 4.
THE OFFICIAL INTENSITY FORECAST IS BASICALLY IN LINE WITH THE
STATISTICAL AND INTENSITY CONSENSUS AIDS AND HIGHER THAN THE
PREVIOUS ONE THROUGH 48 HOURS TO ACCOUNT FOR CURRENT TRENDS. 
BEYOND THAT TIME...IT IS ESSENTIALLY THE SAME.
 
THE CENTER APPEARS TO BE FARTHER SOUTH RELATIVE TO THE PREVIOUS
ESTIMATE...AND IT IS UNKNOWN WHETHER THIS REPRESENTS A REFORMATION
OF THE CENTER OR AN ACTUAL MOVEMENT. THE LATEST FIXES YIELD A
LONGER-TERM MOTION OF 095/05.  THE INTERACTION OF IRWIN AND A
MID-TROPOSPHERIC LOW SOUTHWEST OF BAJA CALIFORNIA SHOULD RESULT IN
A BRIEF TURN TOWARD THE EAST-NORTHEAST OR NORTHEAST WITH AN
INCREASE IN FORWARD SPEED DURING THE NEXT DAY OR TWO. THE GUIDANCE
THEN DEPICTS IRWIN BEING PULLED EASTWARD AND THEN SOUTHEASTWARD
INTO A BROAD MONSOON-TYPE FLOW TO THE SOUTH OF MEXICO.  AFTER
BECOMING A REMNANT LOW...MOST OF THE GLOBAL MODELS TURN THE SYSTEM
BACK TO THE WEST AS A LOW-LEVEL RIDGE BUILDS TO THE NORTH. THE
OFFICIAL FORECAST HAS BEEN MODIFIED TO INDICATE THIS SCENARIO AND
IS NEAR BUT GENERALLY A LITTLE FASTER THAN THE PREVIOUS ONE BETWEEN
24-72 HOURS...TO THE RIGHT OF THE MULTI-MODEL CONSENSUS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  11/2100Z 14.9N 114.2W   40 KT  45 MPH
 12H  12/0600Z 15.2N 113.1W   45 KT  50 MPH
 24H  12/1800Z 16.1N 110.9W   50 KT  60 MPH
 36H  13/0600Z 17.1N 108.9W   40 KT  45 MPH
 48H  13/1800Z 17.3N 107.0W   35 KT  40 MPH
 72H  14/1800Z 16.7N 104.5W   30 KT  35 MPH
 96H  15/1800Z 16.0N 105.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  16/1800Z 15.5N 106.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER KIMBERLAIN
 
NNNN


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Page last modified: Tuesday, 17-Jul-2012 13:44:20 UTC