WTPZ45 KNHC 260256 RRA

TCDEP5



HURRICANE IRWIN DISCUSSION NUMBER  15

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102017

800 PM PDT TUE JUL 25 2017



IRWIN HAS STRENGTHENED A LITTLE MORE DURING THE PAST SEVERAL HOURS.

THE EYE OF THE HURRICANE HAS BEEN OCCASIONALLY EVIDENT IN

SATELLITE IMAGES AND CLOUD TOPS IN THE EYEWALL ARE QUITE COLD,

CLOSE TO -80 C.  THE CONVECTIVE STRUCTURE IS ASYMMETRIC, HOWEVER,

WITH THE MAJORITY OF THE DEEPEST CONVECTION LOCATED TO THE WEST OF

THE CENTER.  THE LATEST DVORAK CLASSIFICATIONS HAVE INCREASED

SLIGHTLY, AND SUPPORT NUDGING THE INITIAL INTENSITY UPWARD TO 80 KT.



IRWIN IS MOVING WESTWARD AT 7 KT AS IT IS STILL BEING STEERED BY A

MID-LEVEL RIDGE TO ITS NORTHEAST.  A TURN TO THE WEST-SOUTHWEST IS

EXPECTED TONIGHT AND WEDNESDAY AS HURRICANE HILARY APPROACHES FROM

THE EAST.  THE FORWARD MOTION OF IRWIN WILL LIKELY COME TO A HALT ON

THURSDAY AND FRIDAY AS HILARY PASSES BY TO THE NORTH.  AFTER THAT

TIME, A GENERAL NORTHWARD MOTION IS EXPECTED AS IRWIN GETS CAUGHT IN

THE FLOW ON THE EAST SIDE OF HILARY'S CIRCULATION.  THE MODELS ARE

IN BETTER AGREEMENT COMPARED TO PREVIOUS CYCLES, BUT THERE IS STILL

A FAIR AMOUNT OF SPREAD IN WHERE AND WHEN IRWIN MAKES THE NORTHWARD

TURN.  THE NHC TRACK FORECAST IS LARGELY AN UPDATE OF THE PREVIOUS

ONE, AND LIES CLOSEST TO THE MULTI-MODEL CONSENSUS TVCE.



THE HURRICANE COULD BE NEARING ITS PEAK INTENSITY, AND WEAKENING

SHOULD COMMENCE SOON DUE TO MODERATE WIND SHEAR AND THE POTENTIAL

FOR COLD WATER UPWELLING DUE TO THE EXPECTED SLOW MOTION OF IRWIN.

BY THE END OF THE FORECAST PERIOD, IRWIN WILL BE MOVING OVER MUCH

COOLER SSTS AND INTO A DRIER AIR MASS, WHICH SHOULD CONTINUE THE