WTPZ42 KNHC 200236 RRA

TCDEP2



TROPICAL STORM GREG DISCUSSION NUMBER  11

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072017

900 PM MDT WED JUL 19 2017



GREG'S CONVECTIVE PATTERN HAS NOT IMPROVED THIS EVENING, WITH MOST

OF THE ASSOCIATED SHOWER AND THUNDERSTORM ACTIVITY CONCENTRATED TO

THE SOUTH AND WEST OF THE CENTER.  SINCE SUBJECTIVE AND OBJECTIVE

DVORAK ESTIMATES HAVE EITHER REMAINED STEADY OR FALLEN FROM SIX

HOURS AGO, THE INITIAL INTENSITY IS HELD AT 40 KT BASED ON THE

EARLIER ASCAT PASSES.



GREG'S INITIAL MOTION IS WESTWARD, OR 270/9 KT.  A STRONG MID- TO

UPPER-LEVEL RIDGE AXIS EXTENDING WESTWARD FROM NORTHERN MEXICO

SHOULD CAUSE GREG TO MOVE WESTWARD OR WEST-NORTHWESTWARD FOR THE

ENTIRE FORECAST PERIOD, BUT AT A SLIGHTLY FASTER FORWARD SPEED

BEGINNING IN ABOUT 24 HOURS.  THE BIGGEST FORECAST CHALLENGE FOR

GREG'S TRACK IS ITS FORWARD SPEED, SINCE THERE IS A NOTABLE

DIFFERENCE BETWEEN THE FASTER ECMWF AND THE SLOWER GFS AND HWRF

MODELS.  LONGITUDE-WISE, THE UPDATED NHC FORECAST IS CLOSE TO THE

TVCN MULTI-MODEL CONSENSUS.  HOWEVER, A SLIGHT SHIFT IN THE OVERALL

GUIDANCE ENVELOPE REQUIRED A BIT OF A SOUTHWARD NUDGE COMPARED TO

THE PREVIOUS FORECAST.



IT'S NOT EXACTLY CLEAR WHY GREG'S CONVECTION HAS NOT BECOME ANY

BETTER ORGANIZED SINCE THE ANALYZED DEEP-LAYER SHEAR IS LESS THAN 10

KT.  HOWEVER, PRODUCTS FROM UW-CIMSS DO SUGGEST THAT THERE IS 15-20

KT OF MID-LEVEL SHEAR EXTENDING NORTHEAST OF GREG'S CENTER, WHICH

COULD BE DISRUPTING THE CONVECTION IN THAT QUADRANT.  ASSUMING THAT

THE AMBIENT ENVIRONMENT SLOWLY IMPROVES OVER TIME, GREG SHOULD BE

ABLE TO EVENTUALLY BECOME BETTER ORGANIZED AND STRENGTHEN AS