WTPZ45 KNHC 201435 RRA

TCDEP5



TROPICAL STORM DARBY DISCUSSION NUMBER  36

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016

800 AM PDT WED JUL 20 2016



DARBY CONTINUES TO BE RELATIVELY STEADY STATE, WITH CONVECTIVE CLOUD

TOPS OF -50C TO -60C NEAR THE CENTER.  AN AMSR2 PASS AT 1017Z SHOWED

THAT THE LOW-LEVEL CENTER IS LOCATED SOUTHWEST OF THE MID-LEVEL

CENTER SEEN IN GEOSTATIONARY IMAGERY.  THE INITIAL INTENSITY IS SET

TO 50 KT BASED ON A BLEND OF THE LATEST DVORAK ESTIMATES OF T3.5/55

KT FROM TAFB AND T3.0/45 KT FROM SAB.  DARBY WILL MOVE OVER SLIGHTLY

WARMER WATERS IN THE NEXT COUPLE OF DAYS, BUT THIS SHOULD BE

COUNTERACTED BY MODERATE SOUTHWESTERLY SHEAR AND A GENERALLY DRY

ATMOSPHERIC ENVIRONMENT.  THE SHIPS AND LGEM MODELS SHOW STEADY

WEAKENING, WHILE THE DYNAMICAL MODELS ARE SHOWING SOME

RESTRENGTHENING THROUGH 48 HOURS.  GIVEN THIS, THE OFFICIAL FORECAST

CONTINUES TO SHOW LITTLE CHANGE IN INTENSITY DURING THE FIRST 48

HOURS.  THE SHEAR INCREASES LATE IN THE PERIOD WHILE SSTS WILL COOL

BELOW 26C ALONG THE TRACK, WHICH SHOULD RESULT IN SOME SLOW

WEAKENING.  THE NEW NHC FORECAST IS CLOSE TO THE LATEST INTENSITY

CONSENSUS AID.



THE INITIAL MOTION ESTIMATE IS 270/10.  DARBY IS EXPECTED TO MOVE A

LITTLE SOUTH OF DUE WEST FOR THE NEXT 48 HOURS UNDER THE INFLUENCE

OF A MID-LEVEL RIDGE BUILDING SOUTHEASTWARD FROM NORTH OF THE

HAWAIIAN ISLANDS.  AFTER THAT TIME, A BREAK IN THE RIDGE DEVELOPS AS

AN UPPER-LEVEL LOW RETROGRADES WESTWARD WELL NORTH OF HAWAII, WHICH

SHOULD CAUSE DARBY TO TURN SHARPLY NORTHWESTWARD BY DAY 4 AND THEN

NORTH-NORTHWESTWARD ON DAY 5.  MOST OF MODEL GUIDANCE REMAINS IN

GOOD AGREEMENT ON THIS TRACK SCENARIO, HOWEVER, THERE ARE STILL SOME