WTNT42 KNHC 242034 RRA

TCDAT2



TROPICAL STORM GASTON DISCUSSION NUMBER   9

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016

500 PM AST WED AUG 24 2016



GASTON IS BEING AFFECTED BY SOUTHWESTERLY VERTICAL SHEAR ASSOCIATED

WITH A STRONG MID- TO UPPER-LEVEL TROUGH AND CUT-OFF LOW SEEN IN

WATER VAPOR IMAGERY NEAR 26N 51W.  THE SHEAR HAS CAUSED THE

LOW-LEVEL CENTER TO BECOME PARTIALLY EXPOSED WHILE MUCH OF THE

DEEP CONVECTION HAS BEEN SHUNTED TO EASTERN HALF OF THE CIRCULATION.

IN SPITE OF THE DEGRADED SATELLITE PRESENTATION, DROPSONDE DATA

FROM THE UNMANNED NASA GLOBAL HAWK AIRCRAFT INVESTIGATING GASTON

SUPPORT KEEPING THE INTENSITY AT 60 KT.  IN FACT, ADDITIONAL

OBSERVATIONS FROM THE ONGOING MISSION MIGHT REVEAL THAT THE SYSTEM

IS EVEN A LITTLE STRONGER THAN THIS ESTIMATE.



GASTON IS IN FOR A PROLONGED PERIOD OF STRONG SOUTHWESTERLY SHEAR

FOR THE NEXT 36 TO 48 HOURS, WITH THE SHEAR POSSIBLY PEAKING AROUND

30 KT DURING THAT TIME.  THE CONSIDERABLE SHEAR IS EXPECTED TO

INDUCE WEAKENING, AND IT IS POSSIBLE THAT MORE WEAKENING COULD OCCUR

THAN INDICATED IN THE FORECAST DESPITE THE CYCLONE'S MOVING OVER

WARMER WATERS.  ONCE GASTON'S INTERACTION WITH THE TROUGH LESSENS IN

ABOUT 2 DAYS, THE CYCLONE SHOULD REACH 29 DEG C WATER WHEN THE

SHEAR DIMINISHES.  THIS SHOULD GIVE GASTON AN OPPORTUNITY TO

RE-INTENSIFY FOR AT LEAST A COUPLE OF DAYS BEFORE THE MODELS

INDICATE AN INCREASE IN SHEAR AT THE END OF THE FORECAST PERIOD.

THE INTENSITY FORECAST IS REDUCED RELATIVE TO THE PREVIOUS ONE AND

IS A LITTLE BELOW THE MULTI-MODEL CONSENSUS THROUGH 48 HOURS, BUT

THEN REVERSES AND IS ABOVE THE CONSENSUS AIDS FROM 72-120 HOURS.=