ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IRWIN DISCUSSION NUMBER 27 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 PM PDT WED OCT 12 2011 CONVECTION ASSOCIATED WITH IRWIN HAS DECREASED THIS AFTERNOON...WITH THE LOW-LEVEL CENTER EXPOSED TO THE EAST OF A SMALL AREA OF SHOWERS OR THUNDERSTORMS. AN ASCAT OVERPASS AT 1630 UTC SHOWED SEVERAL 35 KT WIND BARBS SOUTH OF THE CENTER...AND BASED ON THIS IRWIN REMAINS A TROPICAL STORM FOR THIS ADVISORY. THE SCATTEROMETER DATA WAS ALSO USED TO REVISE THE INITIAL AND FORECAST WIND RADII. THE INITIAL MOTION IS NOW 060/15. WATER VAPOR IMAGERY INDICATES AN UPPER-LEVEL LOW NEAR 19N117W...WHICH IS LIKELY HELPING TO STEER THE CYCLONE EAST-NORTHEASTWARD. AFTER 12-24 HOURS...THE DYNAMICAL MODELS FORECAST A MID/UPPER-LEVEL RIDGE TO BUILD NORTH OF THE TROPICAL CYCLONE. AT THE SAME TIME...IRWIN IS FORECAST TO ENCOUNTER LOW-LEVEL WESTERLY FLOW ASSOCIATED WITH A MONSOON-TYPE CIRCULATION DEVELOPING TO THE EAST. THESE FACTORS SHOULD CAUSE IRWIN TO TURN EASTWARD AND THEN SOUTHEASTWARD FROM 24-48 HOURS WITH A DECREASE IN FORWARD SPEED. AFTER THAT...THE RIDGE TO THE NORTH IS FORECAST TO BECOME THE DOMINANT STEERING INFLUENCE...CAUSING IRWIN TO TURN WESTWARD TO COMPLETE A LOOP OR HAIRPIN TURN. THE NEW FORECAST TRACK IS FASTER THAN AND NORTH OF THE PREVIOUS TRACK DURING THE FIRST 48 HOURS BASED MAINLY ON THE INITIAL POSITION AND MOTION. AFTER 48 HOURS IT LIES JUST NORTH OF THE PREVIOUS FORECAST. THE NEW TRACK IS NEAR THE CENTER OF THE TRACK GUIDANCE ENVELOPE. EASTERLY SHEAR IS LIKELY TO CONTINUE THROUGH THE FORECAST PERIOD DUE TO THE UPPER-LEVEL ANTICYCLONE ASSOCIATED WITH JOVA...TROPICAL DEPRESSION TWELVE-E...AND THE DEVELOPING MONSOON CIRCULATION. THE INTENSITY GUIDANCE SHOWS IRWIN SLOWLY WEAKENING THROUGH 48 HOURS... AND SO DOES THE INTENSITY FORECAST. THE INTENSITY FORECAST IS PROBLEMATIC AFTER 48 HOURS DUE TO UNCERTAINTIES IN THE FORECAST UPPER-LEVEL WINDS. DUE TO THE THIS...OFFICIAL FORECAST MAINTAINS THE PREVIOUS SCENARIO OF HAVING IRWIN DEGENERATE TO A REMNANT LOW BY 96 HOURS. HOWEVER... SEVERAL OF THE INTENSITY GUIDANCE MODELS SHOW IRWIN RE-INTENSIFYING AS IT MOVES WESTWARD...AND LATER FORECASTS MAY HAVE TO BE NUDGED IN THAT DIRECTION IF THE MODEL TRENDS CONTINUE. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 16.9N 109.4W 35 KT 40 MPH 12H 13/0600Z 17.7N 107.7W 35 KT 40 MPH 24H 13/1800Z 18.0N 105.6W 30 KT 35 MPH 36H 14/0600Z 17.8N 104.5W 30 KT 35 MPH 48H 14/1800Z 17.0N 103.8W 30 KT 35 MPH 72H 15/1800Z 16.0N 104.5W 30 KT 35 MPH 96H 16/1800Z 16.0N 106.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 17/1800Z 16.0N 109.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER BEVEN NNNN
Alternate Formats
About Alternates -
E-Mail Advisories -
RSS Feeds
Cyclone Forecasts
Latest Advisory -
Past Advisories -
About Advisories
Marine Forecasts
Latest Products -
About Marine Products
Tools & Data
Satellite Imagery -
US Weather Radar -
Aircraft Recon -
Local Data Archive -
Forecast Verification -
Deadliest/Costliest/Most Intense
Learn About Hurricanes
Storm Names
Wind Scale -
Prepare -
Climatology -
NHC Glossary -
NHC Acronyms -
Frequently Asked Questions -
AOML Hurricane-Research Division
About Us
About NHC -
Mission/Vision -
Other NCEP Centers -
NHC Staff -
Visitor Information -
NHC Library
NOAA/
National Weather Service
National Centers for Environmental Prediction
National Hurricane Center
11691 SW 17th Street
Miami, Florida, 33165-2149 USA
nhcwebmaster@noaa.gov
Disclaimer
Privacy Policy
Credits
About Us
Glossary
Career Opportunities
Page last modified: Tuesday, 17-Jul-2012 13:44:19 UTC