WTPZ45 KNHC 301436 RRA

TCDEP5



TROPICAL STORM IRWIN DISCUSSION NUMBER  33

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102017

800 AM PDT SUN JUL 30 2017



EVEN THOUGH IRWIN IS CROSSING THE 26 DEG C ISOTHERM, IT DOES NOT

APPEAR TO BE WEAKENING YET.  IN FACT, RECENT MICROWAVE DATA INDICATE

THE TROPICAL STORM HAS A MID-LEVEL EYE, WHICH HAS OCCASIONALLY

APPEARED IN GEOSTATIONARY SATELLITE IMAGES.  THE SYSTEM IS STILL

PRODUCING A FAIR AMOUNT OF DEEP CONVECTION, ESPECIALLY TO THE SOUTH

OF THE CENTER.  THE LATEST DVORAK CI-NUMBERS FROM TAFB AND SAB ARE

3.5/55 KT AND ACCORDINGLY, THE INITIAL INTENSITY IS SET A BIT HIGHER

TO 55 KT.  THIS WIND SPEED ESTIMATE IS ALSO IN AGREEMENT WITH ASCAT

DATA FROM SEVERAL HOURS AGO THAT SHOWED MAXIMUM WINDS NEAR 50 KT.



DESPITE THE RECENT INCREASE IN INTENSITY, IRWIN IS EXPECTED TO BEGIN

WEAKENING SOON AS IT MOVES OVER EVEN COOLER WATERS AND INTO A DRIER

AND MORE STABLE AIR MASS.  THE STORM IS LIKELY TO BECOME A REMNANT

LOW IN 36 TO 48 HOURS WHEN IT WILL BE OVER SSTS NEAR 22 DEG C.  MOST

OF THE GLOBAL MODELS SHOW THE REMNANT LOW DISSIPATING IN 4 TO 5

DAYS.  THE NHC INTENSITY FORECAST FOLLOWS THE TREND OF THE GUIDANCE,

AND IT IS LARGELY UNCHANGED FROM THE PREVIOUS PREDICTION.



IRWIN IS MOVING NORTH-NORTHWESTWARD, OR 345 DEGREES, AT 8 KT.  THE

SYSTEM IS EMBEDDED IN SOUTH-SOUTHEASTERLY FLOW IN THE WAKE OF

HILARY, AND IT IS EXPECTED TO REMAIN IN THIS STEERING FLOW FOR

ANOTHER DAY OR TWO.  ONCE IRWIN BECOMES A REMNANT LOW, THE SHALLOW

SYSTEM IS EXPECTED TO TURN A LITTLE TO THE LEFT AND SLOW DOWN AS IT

BECOMES STEERED BY THE LOW-LEVEL FLOW.  THE NHC TRACK FORECAST IS

ADJUSTED A LITTLE TO THE NORTH AND EAST OF THE PREVIOUS ONE, TO COME