WTPZ45 KNHC 112033 RRA

TCDEP5



TROPICAL DEPRESSION FIFTEEN-E DISCUSSION NUMBER   1

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP152017

300 PM MDT MON SEP 11 2017



THE REMNANTS OF ATLANTIC HURRICANE KATIA HAVE REDEVELOPED AFTER

REACHING THE PACIFIC OCEAN A COUPLE OF DAYS AGO.  THE SYSTEM

MAINTAINED A MID-LEVEL CIRCULATION WHILE TRANSITING THE HIGH TERRAIN

OF MEXICO, BUT HAD LOST ITS SURFACE CENTER.  YESTERDAY, DEEP

CONVECTION BEGAN IN ASSOCIATION WITH THE MID-LEVEL CIRCULATION AND

TODAY A WELL-DEFINED SURFACE CENTER FORMED.  WHILE IT WAS ORIGINALLY

THOUGHT THAT THE CONVECTION WOULD BE SPORADIC BECAUSE OF THE

MODERATE VERTICAL SHEAR, THE DEEP CONVECTION HAS INSTEAD PERSISTED

CLOSE TO THE SYSTEM'S CENTER DURING THE LAST SEVERAL HOURS.  SINCE

THE SYSTEM NOW MEETS THE DEFINITION OF A TROPICAL CYCLONE,

ADVISORIES ARE INITIATED AS TROPICAL DEPRESSION FIFTEEN.



THE DEPRESSION IS MOVING TOWARD THE WEST AT 13 KT, STEERED

PRIMARILY BY THE DEEP-LAYER RIDGE TO ITS NORTH.  THE OFFICIAL TRACK

FORECAST IS A WESTWARD OR WEST-SOUTHWESTWARD MOTION AT A SLOWER

RATE OF FORWARD SPEED DURING THE NEXT TWO DAYS, THEN A TURN BACK

TOWARD THE WEST OR WEST-NORTHWEST AT DAYS 3 AND 4.  THIS FORECAST

IS BASED UPON A BLEND OF THE GFS AND ECMWF GLOBAL MODELS, AS THE

REMAINING GUIDANCE EITHER DOESN'T KNOW ABOUT THE DEPRESSION OR

UNREALISTICALLY INTENSIFIES IT AND TAKES IT TOWARD THE NORTH.



THE SYSTEM LIKELY WILL NOT BECOME VERY SUBSTANTIAL.  THE MODERATE

SHEAR SHOULD CONTINUE, WHILE THE DEPRESSION HEADS TOWARD COOL SSTS

AND DRY AIR.  THE OFFICIAL INTENSITY FORECAST SHOWS JUST MODEST

STRENGTHENING TO A LOW-END TROPICAL STORM IN ABOUT A DAY, BEFORE