WTPZ45 KNHC 200837 RRA

TCDEP5



TROPICAL STORM DARBY DISCUSSION NUMBER  35

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016

200 AM PDT WED JUL 20 2016



DARBY HAS CHANGED LITTLE IN STRUCTURE DURING THE PAST FEW HOURS.

DEEP CONVECTION WITH CLOUD TOPS AS COLD AS -60C CONTINUE NEAR THE

CENTER, AND RECENT MICROWAVE IMAGES SHOWED A NEARLY CLOSED

MID-LEVEL RING.  DVORAK CURRENT INTENSITY NUMBERS REMAIN 3.5 FROM

TAFB AND SAB, AND THE INITIAL INTENSITY IS THEREFORE HELD AT 55 KT.

DARBY IS OVER SSTS AROUND 25C AND IS HEADING TOWARD WARMER WATERS.

HOWEVER, VERTICAL SHEAR IS EXPECTED TO INCREASE IN THE NEXT 24-36

HOURS.  INTERESTINGLY, THE INTENSITY MODELS AREN'T IN AGREEMENT ON

WHAT WILL HAPPEN WITH DARBY'S INTENSITY DURING THIS PERIOD.  WHILE

THE SHIPS AND LGEM MODELS INDICATE STEADY WEAKENING OVER THE NEXT

FEW DAYS, THE HWRF AND FLORIDA STATE SUPERENSEMBLE ACTUALLY SHOW

SOME RE-INTENSIFICATION IN 24-36 HOURS.  DUE TO THESE COMPETING

SIGNALS, THE NHC OFFICIAL FORECAST SHOWS LITTLE CHANGE IN INTENSITY

DURING THE NEXT 48 HOURS, FOLLOWED BY GRADUAL WEAKENING ON DAYS

3-5.  THIS UPDATED FORECAST IS NOT TOO DIFFERENT FROM THE PREVIOUS

ONE, EXCEPT THAT IT DELAYS STEADY WEAKENING UNTIL AFTER 48 HOURS.



DARBY IS MOVING WESTWARD WITH AN INITIAL MOTION OF 270/11 KT.  THE

CYCLONE IS LOCATED TO THE SOUTH OF THE SUBTROPICAL RIDGE, WHICH

SHOULD MAINTAIN A WESTWARD MOTION FOR THE NEXT THREE DAYS.  AFTER

THAT TIME, A RETROGRADING MID- TO UPPER-LEVEL LOW NORTH OF THE

HAWAIIAN ISLANDS WILL CREATE A BREAK IN THE RIDGE, CAUSING DARBY TO

TURN NORTHWESTWARD AND NORTH-NORTHWESTWARD ON DAYS 4 AND 5.  WITH

THE EXCEPTION OF THE GFDL, THERE IS VERY LITTLE CROSS-TRACK SPREAD=