WTPA43 PHFO 220303 RRA

TCDCP3



TROPICAL STORM DARBY DISCUSSION NUMBER  42

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP052016

500 PM HST THU JUL 21 2016



DARBY'S SATELLITE SIGNATURE HAS IMPROVED SOMEWHAT SINCE THE

PREVIOUS ADVISORY, WITH A CURVED CONVECTIVE BAND WRAPPING INTO THE

CENTER FROM THE NORTH, AND OUTFLOW INCREASING IN THE NORTH AND

NORTHWEST SEMICIRCLES. DVORAK INTENSITY ESTIMATES CONTINUE TO BE

3.0/45 KT FROM HFO/SAB/GTW, BUT THE INITIAL INTENSITY HAS BEEN

MAINTAINED AT 55 KT FOR THIS ADVISORY, AS EARLIER INTENSITY

ESTIMATES MAY HAVE BEEN A LITTLE GENEROUS. INITIAL RECONNAISSANCE

INTO DARBY BY THE 53RD WEATHER RECONNAISSANCE SQUADRON IS SCHEDULED

FOR TOMORROW MORNING, AND THEIR DATA WILL GIVE US A MUCH BETTER

IDEA AS TO DARBY'S INTENSITY AND SIZE.



THE INITIAL MOTION FOR THIS ADVISORY IS ESTIMATED TO BE 270/11 KT,

WITH DARBY CURRENTLY BEING STEERED BY A RETROGRADING MID-LEVEL RIDGE

CENTERED WELL NORTH OF HAWAII.  THIS RIDGE WILL BE THE PRIMARY

STEERING MECHANISM OVER THE NEXT DAY OR SO, AFTER WHICH TIME A DEEP

LAYER LOW DIGGING SOUTHWARD WILL WEAKEN THE RIDGE, RESULTING IN A

REDUCTION IN DARBY'S FORWARD SPEED.  AS THE RIDGE WEAKENS, DARBY IS

EXPECTED TO TURN TOWARD THE NORTHWEST, BUT THE TURN IS NOT EXPECTED

TO BE A SHARP AS EARLIER FORECAST. AS DARBY BEGINS TO GAIN LATITUDE,

IT WILL MOVE NORTH OF A MID-LEVEL RIDGE AXIS EXTENDING TOWARD HAWAII

FROM THE EASTERN PACIFIC, AND BECOME EMBEDDED WITHIN DEEP-LAYER

SOUTH TO SOUTHEAST FLOW THAT TAKES DARBY TOWARD THE NORTHWEST.

LATEST TRACK GUIDANCE SHIFTED TOWARD THE PREVIOUS FORECAST, AND THE

NEW TRACK FORECAST IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ONE.=