WTNT42 KNHC 252038 RRA

TCDAT2



TROPICAL STORM GASTON DISCUSSION NUMBER  13

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016

500 PM AST THU AUG 25 2016



STRONG SOUTHWESTERLY SHEAR CONTINUES TO TAKE A TOLL ON GASTON.  THE

CLOUD PATTERN HAS BECOME MORE ASSYMETRIC WITH ALL OF THE DEEP

CORE CONVECTION LOCATED NORTH AND EAST OF THE CENTER.  THIS WAS

CONFIRMED BY A RECENT SSMIS MICROWAVE OVERPASS THAT SHOWED

SIGNIFICANT SOUTHWEST TO NORTHEAST TILT BETWEEN THE LOW- AND

MID-LEVEL CENTERS.  OBJECTIVE DVORAK T-NUMBERS HAVE DECREASED AND

SUBJECTIVE INTENSITY ESTIMATES FROM TAFB AND SAB SUPPORT AN INITIAL

WIND SPEED OF 55 KT.  A LARGE UPPER-LEVEL LOW NEAR 23N 54W THAT IS

MOVING SOUTHWESTWARD IS EXPECTED TO CONTINUE TO PRODUCE AN

UNFAVORABLE UPPER-LEVEL ENVIRONMENT OVER GASTON FOR ANOTHER 12 TO

18 HOURS.  SOME ADDITIONAL WEAKENING IS POSSIBLE TONIGHT, BUT THE

OFFICIAL NHC FORECAST SHOWS LITTLE CHANGE IN STRENGTH THROUGH

FRIDAY.  AFTER THAT TIME, GASTON SHOULD BE MOVING AROUND THE

NORTHERN PORTION OF THE UPPER-LOW AND INTO A MORE FAVARABLE

UPPER-LEVEL WIND PATTERN.  THIS COMBINED WITH WARM SSTS AND A MOIST

ATMOSPHERE SHOULD ALLOW GASTON TO RE-STRENGTHEN OVER THE WEEKEND

AND ONCE AGAIN BECOME A HURRICANE.  THE UPDATED NHC INTENSITY

FORECAST IS SLIGHTLY ABOVE THE PREVIOUS ADVISORY AFTER 36 HOURS, AND

IS IN GOOD AGREEMENT WITH THE LATEST SHIPS GUIDANCE.



THE INITIAL MOTION REMAINS NORTHWESTWARD AT 15 KT.  GASTON SHOULD

MOVE NORTHWESTWARD DURING THE NEXT DAY OR SO AROUND A MID-LEVEL

RIDGE OVER THE EAST-CENTRAL ATLANTIC.  IN 36 TO 48 HOURS, A RIDGE IS

FORECAST TO BUILD TO THE NORTH OF GASTON, WHICH SHOULD CAUSE THE

CYCLONE TO TURN WEST-NORTHWESTWARD.  EARLY NEXT WEEK, THE RIDGE=