WTNT42 KNHC 142040 RRA

TCDAT2



TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   2

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016

500 PM AST WED SEP 14 2016



THE DEPRESSION HAS NOT BECOME BETTER ORGANIZED SINCE THE LAST

ADVISORY, WITH THE MOST CONCENTRATED CONVECTION NOW IN A CLUSTER

JUST WEST OF THE ESTIMATED CENTER POSITION.  THE INITIAL INTENSITY

REMAINS 30 KT IN BEST AGREEMENT WITH A SATELLITE INTENSITY ESTIMATE

FROM SAB.



THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/13 KT.  A LOW- TO

MID-LEVEL RIDGE SHOULD STEER THE SYSTEM WEST-NORTHWESTWARD AND THEN

WESTWARD DURING THE FORECAST PERIOD, WITH SOME DECREASE IN FORWARD

SPEED AFTER 36-48 HOURS AS THE RIDGE WEAKENS SLIGHTLY.  THE NEW

FORECAST TRACK IS SIMILAR TO, BUT A LITTLE NORTH OF, THE PREVIOUS

TRACK BASED ON A SLIGHT NORTHWARD SHIFT IN THE TRACK GUIDANCE.



SOME STRENGTHENING IS EXPECTED DURING THE NEXT 12 HOURS OR SO. AFTER

THAT, THE CYCLONE WILL ENCOUNTER STRONG WESTERLY VERTICAL WIND SHEAR

CAUSED BY A DEVELOPING UPPER-LEVEL TROUGH NEAR AND NORTH OF THE

CYCLONE.  THIS, COMBINED WITH PASSAGE OVER SEA-SURFACE TEMPERATURES

OF ABOUT 26C-27C, SHOULD LEAD TO WEAKENING, AND THE INTENSITY

FORECAST SHOWS THE SYSTEM WEAKENING BACK TO A DEPRESSION BY 36

HOURS.  NEAR THE END OF THE FORECAST PERIOD, THE DYNAMICAL MODELS

CONTINUE TO DIVERGE ON THE EVOLUTION OF THE UPPER-LEVEL WINDS, WITH

THE ECMWF AND UKMET FORECASTING A MORE FAVORABLE RIDGE PATTERN NEAR

THE CYCLONE, WHEREAS THE GFS HAS AN UPPER-LEVEL TROUGH CLOSE BY.

BASED ON THESE CONFLICTING MODELS, THE FORECAST LEANS TOWARD THE

ECMWF/UKMET SCENARIO AND SHOWS SOME RE-INTENSIFICATION BY 120 HOURS.

AN ALTERNATIVE SCENARIO IS THAT THE CYCLONE DEGENERATES INTO A BROAD=