WTPZ45 KNHC 241458 RRA

TCDEP5



TROPICAL STORM IRWIN DISCUSSION NUMBER   9

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102017

800 AM PDT MON JUL 24 2017



IRWIN'S STRUCTURE CONTINUES TO IMPROVE, WITH THE LOW-LEVEL CENTER

EMBEDDED BENEATH A CDO FEATURE THAT HAS PERSISTED FOR THE PAST

SEVERAL HOURS.  IN ADDITION, RECENT MICROWAVE DATA HAVE REVEALED

THE FORMATION OF A MID-LEVEL EYE.  DVORAK SATELLITE INTENSITY

ESTIMATES NOW RANGE BETWEEN T3.0/45 KT AND T3.5/55 KT, SO THE

INITIAL INTENSITY IS RAISED ACCORDINGLY TO 50 KT.



FOR ONCE, THE TRACK FORECAST FOR A TROPICAL CYCLONE IS MORE

CHALLENGING AND MORE UNCERTAIN THAT ITS INTENSITY FORECAST.  IRWIN

IS EXPECTED TO HAVE SOME BINARY INTERACTION WITH HURRICANE HILARY

BEGINNING IN ABOUT 3 DAYS, BUT THE AMOUNT OF INTERACTION IS STILL

HIGHLY UNCERTAIN.  THE ECMWF, UKMET, AND CANADIAN MODELS ALL SHOW A

STRONG FUJIWHARA INTERACTION, WITH IRWIN SWINGING TO THE EAST AND

NORTHEAST OF HILARY BY DAY 5.  THE GFS SHOWS MUCH LESS INTERACTION,

WITH IRWIN STAYING WELL TO THE SOUTHWEST OF HILARY ON DAY 5, AND

THE REGIONAL HWRF AND HMON MODELS DON'T EVEN SEEM TO KNOW ABOUT

HILARY'S EXISTENCE TO ALLOW AN INTERACTION TO OCCUR.  NEEDLESS TO

SAY, THERE IS SIGNIFICANT, HIGHER-THAN-NORMAL SPREAD IN THE TRACK

GUIDANCE BEGINNING IN ABOUT 72 HOURS.  THE UPDATED NHC TRACK

FORECAST CONTINUES TO SHOW A SLOW WESTWARD MOTION THROUGH DAY 3,

FOLLOWED BY AN ACCELERATION TOWARD THE NORTHWEST AND NORTH-NORTHWEST

ON DAYS 4 AND 5.  AT THE LONGER RANGES, THIS FORECAST IS CLOSEST TO

HCCA, BUT FUTURE ADJUSTMENTS ARE LIKELY DUE TO THE SIGNIFICANT

SPREAD AMONG THE MODELS AND THEIR ENSEMBLE MEMBERS.



SINCE IT APPEARS THAT IRWIN IS DEVELOPING A WELL-DEFINED INNER