WTPZ45 KNHC 251435 RRA

TCDEP5



HURRICANE IRWIN DISCUSSION NUMBER  13

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102017

800 AM PDT TUE JUL 25 2017



RECENT MICROWAVE IMAGERY CONFIRMS THAT IRWIN HAS A WELL-DEFINED

MID-LEVEL EYE, WHICH HAS ALSO BEEN APPARENT IN SHORTWAVE INFRARED

SATELLITE IMAGERY.  ON THE WHOLE, SATELLITE INTENSITY ESTIMATES

HAVE RISEN A LITTLE, SO IRWIN'S INITIAL INTENSITY IS NOW SET AT 70

KT.  VARIOUS SHEAR ANALYSES INDICATE THAT ABOUT 15 KT OF SOUTHERLY

SHEAR HAS DEVELOPED OVER IRWIN, WHICH ISN'T SURPRISING SINCE

MICROWAVE DATA HAS HINTED THAT THE LOW-LEVEL CENTER MAY BE LOCATED

JUST A BIT SOUTH OF THE MID-LEVEL EYE.  THIS SHEAR IS EXPECTED TO

CONTINUE FOR ANOTHER 24 HOURS OR SO, WHICH WILL LIKELY PREVENT

IRWIN FROM ANY ADDITIONAL SIGNIFICANT STRENGTHENING.  AFTER 24

HOURS, IRWIN'S PROXIMITY TO HURRICANE HILARY IS LIKELY TO INDUCE

SOME WEAKENING, AS WELL AS THE POTENTIAL FOR UPWELLING OF COLDER

WATER DUE TO IRWIN'S SLOW MOTION THROUGH 72 HOURS.  MORE

DEFINITIVE WEAKENING IS LIKELY BY DAY 5 AS IRWIN REACHES HIGHER

LATITUDES AND MUCH COLDER WATERS.  THE INTENSITY MODELS ARE FAIRLY

STABLE AT THE MOMENT THE LATEST RUNS DID NOT SUGGEST THAT ANY

CHANGES WERE NEEDED TO THE PREVIOUS FORECAST.  IT SHOULD BE NOTED

THAT WHILE MOST OF THE GLOBAL MODELS MAINTAIN IRWIN AS A SEPARATE

AND DISTINCT CYCLONE FROM HILARY THROUGH DAY 5, THE ECMWF MODEL

INDICATES THAT IRWIN COULD BE ABSORBED BY THAT TIME.



IRWIN APPEARS TO BE MOVING SLOWLY WESTWARD, OR 270/5 KT.  THE

CYCLONE'S FUTURE TRACK WILL LARGELY BE DICTATED ITS THE BINARY

INTERACTION WITH HILARY.  FIRST, AS HILARY APPROACHES FROM THE

EAST, IRWIN IS EXPECTED TO DIP WEST-SOUTHWESTWARD AND SOUTHWESTWARD