WTPZ44 KNHC 070843 RRA

TCDEP4



TROPICAL DEPRESSION FOUR-E DISCUSSION NUMBER   3

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP042016

300 AM MDT THU JUL 07 2016



TROPICAL DEPRESSION FOUR-E HAS CHANGED LITTLE OVERNIGHT. A 0458Z

ASCAT-B OVERPASS INDICATED A BROAD, WEAK INNER-CORE WIND FIELD WITH

THE LOW-LEVEL CENTER LOCATED AT OR SOUTH OF 12N LATITUDE. HOWEVER,

PASSIVE MICROWAVE SATELLITE DATA INDICATE A FAIRLY WELL-DEVELOPED

MID-LEVEL CIRCULATION DISPLACED MORE THAN 30 NMI NORTH-NORTHWEST OF

THE LOW-LEVEL CENTER DUE TO SOUTHEASTERLY VERTICAL WIND SHEAR. THE

ASCAT DATA ALSO INDICATED A COUPLE OF 35-KT SURFACE WIND VECTORS.

HOWEVER, CONVECTION NEAR THE CENTER HAS NOTICEABLY WEAKENED AND

BECOME LESS ORGANIZED SINCE THAT PASS, SO THE CYCLONE IS BEING

MAINTAINED AS A 30-KT DEPRESSION, WHICH IS SUPPORTED BY A BLEND OF

SATELLITE INTENSITY ESTIMATES FROM TAFB, SAB, AND UW-CIMSS.



THE INITIAL MOTION ESTIMATE IS STILL 285/07 KT, BASED PRIMARILY ON A

BLEND OF MICROWAVE AND SCATTEROMETER FIX POSITIONS OF THE LOW-LEVEL

AND MID-LEVEL CIRCULATION CENTERS. DESPITE THE DIFFICULTY IN

LOCATING THE EXACT CENTER OF THE DEPRESSION, THE NHC MODEL GUIDANCE

IS IN REMARKABLY GOOD AGREEMENT ON THE FUTURE TRACK OF THE CYCLONE.

THE STRONG SUBTROPICAL RIDGE TO THE NORTH OF THE DEPRESSION IS

FORECAST TO REMAIN NEARLY STATIONARY THROUGHOUT THE FORECAST PERIOD,

AND EVEN AMPLIFY SOMEWHAT IN 24-72 HOURS, DRIVING THE CYCLONE IN A

GENERAL WESTWARD MOTION. AFTER THAT TIME, THE CYCLONE IS EXPECTED TO

TURN TOWARD THE WEST-NORTHWEST AS THE SYSTEM MOVES AROUND THE

SOUTHWESTERN PERIPHERY OF THE RIDGE. THE NHC OFFICIAL FORECAST TRACK

ESSENTIALLY LIES DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE, AND