WTPZ43 KNHC 251652 RRA

TCDEP3



TROPICAL DEPRESSION EIGHTEEN-E SPECIAL DISCUSSION NUMBER   1

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP182016

1000 AM PDT SUN SEP 25 2016



DEEP CONVECTION ASSOCIATED WITH THE LOW PRESSURE AREA LOCATED WELL

SOUTHWEST OF THE BAJA CALIFORNIA HAS BECOME BETTER ORGANIZED

OVERNIGHT, AND EARLY MORNING VISIBLE SATELLITE IMAGERY INDICATE

THAT THE CIRCULATION HAS BECOME BETTER DEFINED.  BASED ON THESE

OBSERVATIONS, AND DVORAK CLASSIFICATIONS OF T2.0 AND T1.5 FROM

TAFB AND SAB RESPECTIVELY, ADVISORIES ARE BEING INITIATED ON A

30-KT TROPICAL DEPRESSION AT THIS TIME.  THE DEPRESSION IS CURRENTLY

LOCATED OVER WARM WATER AND WITHIN AN AREA OF LOW VERTICAL WIND

SHEAR, WHICH IS FAVORABLE FOR SOME GRADUAL STRENGTHENING TODAY.

HOWEVER, IN ABOUT 24 HOURS, THE TROPICAL CYCLONE IS FORECAST TO MOVE

INTO AN AREA OF HIGHER SOUTHWESTERLY SHEAR CAUSED BY LARGE MID- TO

UPPER-LEVEL LOW AND ASSOCIATED TROUGH OVER NORTHWESTERN MEXICO.  THE

GLOBAL MODELS SUGGEST THAT THE SHEAR WILL BECOME QUITE STRONG IN 36

TO 48 HOURS AS THE CYCLONE BEGINS MOVING OVER COOLER WATERS. THIS

SHOULD RESULT IN A RAPID SPIN DOWN, AND THE SYSTEM IS LIKELY TO

BECOME A POST-TROPICAL REMNANT LOW WITHIN 3 DAYS.  THE OFFICIAL

INTENSITY FOREAST IS SLIGHTLY ABOVE THE SHIPS GUIDANCE BUT IS IN

GOOD AGREEMENT WITH THE INTENSITY CONSENSUS.



SINCE THE DEPRESSION IS STILL IN ITS FORMATIVE STAGE, THE INITIAL

MOTION IS A SOMEWHAT UNCERTAIN 360/4 KT.  THE CYCLONE IS EXPECTED TO

BE STEERED SLOWLY NORTHWARD OR NORTH-NORTHEASTWARD DURING THE NEXT

COUPLE OF DAYS AROUND THE WESTERN PORTION OF A WEAK MID-LEVEL RIDGE

THAT EXTENDS SOUTHWESTWARD FROM SOUTHERN MEXICO.  BY 72 HOURS, THE=