000
WTPZ43 KNHC 011448
TCDEP3
TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP182009
800 AM PDT THU OCT 01 2009
 
OVERNIGHT SCATTEROMETER AND MICROWAVE DATA INDICATE THAT THE
CIRCULATION ASSOCIATED WITH THE BROAD LOW PRESSURE AREA SOUTHWEST
OF THE SOUTHERN TIP OF BAJA CALIFORNIA HAS BECOME BETTER DEFINED.
CONVECTION HAS INCREASED THIS MORNING AND SHOWS SUFFICIENT
ORGANIZATION TO CLASSIFY THE SYSTEM AS A TROPICAL DEPRESSION.
THE DEPRESSION IS MOVING WEST-NORTHWESTWARD TO THE SOUTH OF
MID-LEVEL RIDGE THAT EXTENDS FROM NORTHERN MEXICO WESTWARD INTO THE
EASTERN PACIFIC.  THE RIDGE IS FORECAST TO WEAKEN WITHIN THE NEXT
DAY OR SO AS A DEEP-LAYER TROUGH AMPLIFIES ALONG THE WEST COAST OF
THE UNITED STATES.  THE MODELS RESPOND BY TURNING THE CYCLONE
NORTHWARD AND THEN NORTHEASTWARD.  THE GFDL...HWRF...AND ECMWF
MODELS ALL SHOW A STRONGER AND VERTICALLY DEEPER SYSTEM THAT TURNS
NORTHEASTWARD AND ACCELERATES TOWARD THE BAJA PENINSULA. ON THE
OTHER HAND...THE GFS...UKMET...AND NOGAPS WHICH DEPICT A WEAKER
CYCLONE...PREDICT A LATER TURN AND LESS OF A NORTHEASTWARD MOTION.
THE OFFICIAL FORECAST LEANS TOWARD THE LATER SOLUTION...BUT
DOES SHOW A NORTHEAST TURN BEFORE DISSIPATION...IN GENERAL
AGREEMENT WITH THE SHALLOW BAM MODEL.
 
THE DEPRESSION DOES NOT APPEAR TO HAVE MUCH OF AN OPPORTUNITY TO
STRENGTHEN.  SOUTHERLY TO SOUTHWESTERLY VERTICAL SHEAR IS FORECAST
TO INCREASE LATER TODAY AND BECOME STRONGER THEREAFTER.  THE SYSTEM
WILL BE ALSO BE MOVING OVER GRADUALLY DECREASING SSTS.  THE
OFFICIAL FORECAST ALLOWS FOR SLIGHT INTENSIFICATION TODAY...
FOLLOWED BY WEAKENING TO A REMNANT LOW IN ABOUT 48 HOURS.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/1500Z 19.0N 117.9W    30 KT
 12HR VT     02/0000Z 19.4N 119.0W    35 KT
 24HR VT     02/1200Z 19.8N 119.7W    35 KT
 36HR VT     03/0000Z 20.3N 120.1W    30 KT
 48HR VT     03/1200Z 21.3N 120.0W    25 KT...REMNANT LOW
 72HR VT     04/1200Z 23.0N 118.5W    20 KT...REMNANT LOW
 96HR VT     05/1200Z...DISSIPATED
 
$$
FORECASTER BROWN