WTNT43 KNHC 200841 RRA

TCDAT3



TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   3

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132016

500 AM AST TUE SEP 20 2016



THE CLOUD PATTERN OF THE DEPRESSION IS ONLY SLIGHTLY BETTER

ORGANIZED THAN YESTERDAY, WITH SOME BROKEN CONVECTIVE BANDING OVER

THE NORTHEASTERN PORTION OF THE CIRCULATION.  OVERALL, HOWEVER, THE

SYSTEM IS ELONGATED FROM SOUTHWEST TO NORTHEAST.  THE INITIAL

INTENSITY IS HELD AT 30 KT, IN AGREEMENT WITH DVORAK ESTIMATES FROM

BOTH TAFB AND SAB.  THE TROPICAL CYCLONE IS EXPECTED TO REMAIN IN A

LOW SHEAR ENVIRONMENT FOR THE NEXT 48 HOURS OR SO, AND THEREFORE

SOME STRENGTHENING IS FORECAST DURING THAT TIME FRAME.  LATER IN

THE PERIOD, THE DYNAMICAL ENVIRONMENT IS LIKELY TO BECOME HOSTILE

FOR STRENGTHENING SINCE SHEAR ASSOCIATED WITH AN UPPER-LEVEL TROUGH

IS FORECAST TO INCREASE TO AROUND 30 KT IN 3-4 DAYS.  GIVEN THIS

EXPECTED CHANGE IN THE LARGE-SCALE ENVIRONMENT, WEAKENING SHOULD

BEGIN IN 2-3 DAYS AND THE SYSTEM IS PREDICTED TO REVERT TO TROPICAL

DEPRESSION STATUS BY THE END OF THE FORECAST PERIOD. ALTHOUGH THE

DYNAMICAL GUIDANCE SHOWS SOME RELAXATION OF THE SHEAR AT THE END OF

THE PERIOD, THE CURRENT THINKING IS THAT BY THAT TIME THE SYSTEM

WILL BE TOO DISRUPTED TO BE ABLE TO RECOVER.  THE OFFICIAL INTENSITY

FORECAST IS CLOSE TO THE LGEM GUIDANCE THROUGH 72 HOURS AND A LITTLE

BELOW IT AT DAYS 4 AND 5.



THERE IS CONSIDERABLE SPREAD IN CENTER FIXES AND THE INITIAL MOTION

IS AN UNCERTAIN 295/8 KT.  A WEAKNESS IN THE SUBTROPICAL RIDGE

ALONG 30W-40W IS LIKELY TO INDUCE A MORE NORTHWESTWARD TRACK

DURING THE NEXT DAY OR SO, FOLLOWED BY A RETURN TO A WEST-=