WTPZ42 KNHC 210236 RRA

TCDEP2



TROPICAL STORM GREG DISCUSSION NUMBER  15

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072017

800 PM PDT THU JUL 20 2017



GREG'S CENTER IS EMBEDDED BETWEEN A LARGE AND PERSISTENT BAND OF

CONVECTION TO THE SOUTH AND NEWLY DEVELOPING CONVECTION TO THE

NORTHEAST, BUT THE BANDING CONTINUES TO HAVE A TOUGH TIME WRAPPING

AROUND THE NORTHWESTERN SIDE OF THE CIRCULATION.  SINCE DVORAK

ESTIMATES FROM TAFB AND SAB HAVE NOT CHANGED ALL DAY, AND FINAL-T

ADT NUMBERS HAVE ACTUALLY DECREASED, THE INITIAL INTENSITY WILL

REMAIN 45 KT.



GREG IS LOCATED TO THE SOUTH OF ANOMALOUSLY STRONG LOW- TO

MID-LEVEL RIDGING, WHICH IS PUSHING THE CYCLONE WESTWARD WITH AN

INITIAL MOTION OF 275/9 KT.  GREG IS FORECAST TO MOVE ON A WESTWARD

OR WEST-NORTHWESTWARD COURSE FOR THE REST OF THE FORECAST PERIOD,

AND THERE IS GOOD MODEL AGREEMENT THROUGH 48 HOURS.  AFTER 48

HOURS, HOWEVER, THE SPREAD IN THE MODEL GUIDANCE IS LARGER THAN

NORMAL.  THE GFS AND HWRF, FOR EXAMPLE, SHOW A STRONGER GREG MOVING

MORE SLOWLY TOWARD THE NORTHWEST BY DAY 5.  ON THE OTHER HAND, THE

ECMWF AND UKMET HAVE A WEAKER GREG MOVING FASTER AND STAYING

FARTHER SOUTH, WITH SOME INTERACTION WITH THE REMNANTS OF T.D.

EIGHT-E STILL POSSIBLE.  AS A COMPROMISE BETWEEN THESE TWO

SCENARIOS, THE UPDATED OFFICIAL FORECAST IS JUST A LITTLE SLOWER

AND SOUTH OF THE PREVIOUS FORECAST ON DAYS 3 THROUGH 5, AND IT IS

NOT TOO FAR FROM THE VARIOUS MODEL CONSENSUS AIDS.



THE ENVIRONMENT SEEMS AS THOUGH IT SHOULD BE CONDUCIVE FOR

STRENGTHENING.  HOWEVER, GREG HAS DEFIED THAT THOUGHT FOR THE PAST

DAY OR SO, AS IT SEEMS THAT SOMETHING ABOUT ITS STRUCTURE HAS