WTPZ43 KNHC 072033 RRA

TCDEP3



TROPICAL STORM KRISTY DISCUSSION NUMBER   4

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132018

200 PM PDT TUE AUG 07 2018



GEOSTATIONARY SATELLITE AND MICROWAVE IMAGES INDICATE THAT KRISTY

HAS WELL-DEFINED CURVED BANDS, BUT THE CONVECTION IN THESE BANDS

HAS DECREASED DURING THE PAST SEVERAL HOURS.  A RECENT ASCAT PASS

SHOWED MAXIMUM WINDS OF ABOUT 40 KT.  BASED ON THAT DATA AND DVORAK

CLASSIFICATIONS, THE INITIAL INTENSITY IS AGAIN HELD AT 45 KT.



KRISTY HAS BEEN MOVING JUST SOUTH OF DUE WEST DURING THE PAST 12

HOURS, AND THE INITIAL MOTION ESTIMATE IS 260/11 KT.  THE MODELS

AGREE THAT A DECREASE IN FORWARD SPEED AND A TURN TO THE

WEST-NORTHWEST IS EXPECTED TO BEGIN TONIGHT OR ON WEDNESDAY, BUT

THAT IS ABOUT ALL THEY AGREE ON FOR THE FUTURE TRACK OF KRISTY.

THERE REMAINS SIGNIFICANT SPREAD IN THE MODELS ABOUT HOW THE STORM

WILL INTERACT WITH HURRICANE JOHN TO ITS NORTHEAST.  THE GFS

CONTINUES TO SHOW KRISTY BEING PULLED NORTHWARD AND THEN

NORTHEASTWARD INTO THE OUTER CIRCULATION OF JOHN. ON THE OTHER HAND,

THE ECMWF HAS BEEN CONSISTENT IN SHOWING LITTLE INTERACTION BETWEEN

THE TROPICAL CYCLONES, AND KEEPS KRISTY MOVING ON A WESTWARD OR

WEST-NORTHWESTWARD PATH.  THE NHC OFFICIAL TRACK FORECAST LIES

BETWEEN THESE SCENARIOS AND IS CLOSE TO THE RECENT RUN OF THE UKMET

MODEL.  THIS FORECAST HAS BEEN ADJUSTED TO THE NORTH AND EAST OF THE

PREVIOUS ONE TO GET CLOSER TO THE MIDDLE OF THE GUIDANCE ENVELOPE.

IT SHOULD BE NOTED THAT THE TRACK FORECAST IS OF LOW CONFIDENCE

GIVEN THE VERY DIFFERENT MODEL SOLUTIONS.



KRISTY'S STRUGGLES ARE LIKELY DUE TO THE INFLUENCES OF DRY AIR AND

MODERATE SHEAR.  THE SHIPS MODEL SHOWS THE SHEAR DECREASING DURING