WTPZ42 KNHC 220253 RRA

TCDEP2



TROPICAL STORM GREG DISCUSSION NUMBER  19

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072017

800 PM PDT FRI JUL 21 2017



GREG IS CONTINUING TO EXPERIENCE SIGNIFICANT VERTICAL SHEAR, AS THE

DEEP CONVECTION IS ONLY OBSERVED IN THE NORTHEASTERN SEMICIRCLE AND

ITS CENTER IS ON THE EDGE OF THE CONVECTIVE OVERCAST.  A BLEND OF

SUBJECTIVE DVORAK ESTIMATES FROM SAB/TAFB, OBJECTIVE DVORAK FROM

CIMSS, AND AN ATMS ANALYSIS ALL SUGGEST ABOUT 45 KT MAXIMUM

SUSTAINED WINDS, UNCHANGED FROM THE PREVIOUS ADVISORY.



VERTICAL SHEAR ANALYSIS FROM CIMSS SUGGESTS SUBSTANTIALLY STRONGER

TROPOSPHERIC VERTICAL SHEAR THAN ANALYZED BY EITHER THE GFS OR

ECMWF GLOBAL MODELS.  THE SOUTHWESTERLY SHEAR APPEARS TO DUE TO A

VIGOROUS UPPER-LEVEL TROUGH NORTH-NORTHWEST OF GREG.  WHILE THE

SHEAR SHOULD SUBSIDE SOME AS THE UPPER TROUGH AND GREG MOVE AWAY

FROM EACH OTHER, THE ATMOSPHERE THAT GREG WILL MOVE THROUGH SHOULD

BECOME PROGRESSIVELY DRIER AND MORE STABLE.  AROUND DAY 5, THE

HOSTILE THERMODYNAMICS ARE EXPECTED TO CAUSE GREG TO LOSE DEEP

CONVECTION COMPLETELY AND THUS BECOME A REMNANT LOW.  THE OFFICIAL

INTENSITY FORECAST  - SHOWING LITTLE TO NO INTENSIFICATION BEFORE A

GRADUAL DECAY STARTING AROUND DAY 3 - IS BASED UPON THE HCCA

CORRECTED CONSENSUS TECHNIQUE AND IS SLIGHTLY LOWER THAN THAT OF THE

PREVIOUS ADVISORY.



GREG IS MOVING TOWARD THE WEST AT ABOUT 12 KT, AS IT IS MOVING

ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE.  A GRADUAL

BEND TOWARD THE WEST-NORTHWEST IS ANTICIPATED AROUND DAY 4 AND 5,

AS A WEAKENING GREG SHOULD BE ADVECTED ALONG BY THE LOW-LEVEL

TRADES.  THE MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THIS SCENARIO -