WTPZ42 KNHC 210844 RRA

TCDEP2



TROPICAL STORM GREG DISCUSSION NUMBER  16

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072017

200 AM PDT FRI JUL 21 2017



A BAND OF DEEP CONVECTION REMAINS WRAPPED AROUND THE EASTERN HALF

OF THE CIRCULATION, BUT LITTLE CONVECTION IS PRESENT ON THE WESTERN

SIDE OF THE CYCLONE.  SINCE THE CONVECTIVE STRUCTURE IS MORE OR

LESS THE SAME AS BEFORE, DVORAK ESTIMATES FROM TAFB AND SAB ARE

UNCHANGED, AND THE INITIAL INTENSITY IS HELD AT 45 KT.



BOTH THE TRACK AND INTENSITY FORECASTS ARE CHALLENGING.  THE

INTENSITY GUIDANCE SPREAD IS HIGH, RANGING FROM THE COAMPS-TC

MODEL, WHICH MAKES GREG A MAJOR HURRICANE IN 3 DAYS, TO THE LGEM,

WHICH PEAKS AT 49 KT.  BASED ON THE SHIPS DIAGNOSTICS FROM BOTH THE

GFS AND ECMWF FORECAST FIELDS, THE WARM SST, LOW SHEAR ENVIRONMENT

WOULD SEEM TO SUPPORT STRENGTHENING IN THE SHORT TERM.  ON THE

FORECAST TRACK, GREG SHOULD ENCOUNTER A DRIER AND MORE STABLE

ENVIRONMENT THAT SHOULD BRING A HALT TO ANY INTENSIFICATION AFTER

ABOUT 72 HOURS.  THE NHC FORECAST IS CLOSE TO THE HWRF MODEL FOR THE

FIRST 48 HOURS, AND STILL SHOWS GREG REACHING HURRICANE STRENGTH.

AFTER THAT, THE HWRF AND COAMPS-TC MODELS SHOW CONTINUED

INTENSIFICATION, BUT THAT SEEMS UNLIKELY IN WHAT IS EXPECTED TO BE

AN UNFAVORABLE ENVIRONMENT.  THE NHC FORECAST INSTEAD FOLLOWS THE

TREND OF THE STATISTICAL MODELS LATE IN THE PERIOD AND SHOWS STEADY

WEAKENING.



THE CENTER HAS BEEN DIFFICULT TO LOCATE TONIGHT, AND THE INITIAL

MOTION IS AN UNCERTAIN 280/9 KT.  FOR THE FIRST 48 HOURS OR SO, GREG

SHOULD CONTINUE ON A WEST OR WEST-NORTHWEST HEADING, BELOW A LOW TO

MID-LEVEL RIDGE. BEYOND THAT, THERE IS TREMENDOUS SPREAD IN THE