WTNT42 KNHC 251440 RRA

TCDAT2



TROPICAL STORM GASTON DISCUSSION NUMBER  12

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016

1100 AM AST THU AUG 25 2016



THE SATELLITE PRESENTATION OF GASTON HAS DEGRADED SOME SINCE THE

PREVIOUS ADVISORY, WITH DEEP CONVECTION BURSTING NORTHEAST OF THE

CENTER DUE TO ABOUT 25 KT OF SOUTHWESTERLY SHEAR AS ANALYZED BY

UW-CIMSS.  AN ASCAT-B PASS FROM 1212 UTC WAS HELPFUL IN LOCATING THE

CENTER AND SHOWED PEAK WINDS OF AROUND 55 KT, WHICH SUPPORT AN

INTENSITY OF 60 KT FOR THIS ADVISORY, A LITTLE ABOVE THE LATEST

DVORAK ESTIMATES OF T3.5/55 KT.  THE STRONG SHEAR IS FORECAST TO

CONTINUE FOR THE NEXT 24 HOURS UNTIL GASTON MOVES POLEWARD OF AN

UPPER-LEVEL LOW CURRENTLY LOCATED TO ITS WEST.  GIVEN THE SHEAR AND

SSTS AROUND 27-28C, LITTLE CHANGE IN INTENSITY, OR PERHAPS SOME

SLIGHT WEAKENING, IS EXPECTED IN THE FIRST 24 HOURS.  AFTER THAT

TIME, THE SHEAR DECREASES AND GASTON MOVES OVER SSTS OF 29-30C,

WHICH SHOULD ALLOW FOR STRENGTHENING THROUGH THE REST OF THE

FORECAST PERIOD.  THE NHC INTENSITY FORECAST IS A LITTLE HIGHER THAN

THE PREVIOUS ONE LATER IN THE PERIOD AND IS CLOSE TO THE SHIPS MODEL

AND THE IVCN INTENSITY CONSENSUS.



THE INITIAL MOTION ESTIMATE IS 315/15.  GASTON SHOULD CONTINUE

MOVING QUICKLY NORTHWESTWARD FOR THE NEXT 24 TO 36 HOURS AROUND A

MID-LEVEL RIDGE CENTERED TO ITS NORTHEAST.  RIDGING THEN BUILDS

WESTWARD TO THE NORTH OF THE TROPICAL CYCLONE, LEADING TO A DECREASE

IN FORWARD SPEED AND A TURN TOWARD THE WEST-NORTHWEST IN 48 HOURS.

LATE IN THE PERIOD, GASTON WILL TURN POLEWARD INTO A WEAKNESS ALONG

60W AND THEN BEGIN TO RECURVE INTO THE MID-LATITUDE WESTERLIES.  THE=