WTPA43 PHFO 211436 RRA

TCDCP3



TROPICAL STORM DARBY DISCUSSION NUMBER  40

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP052016

500 AM HST THU JUL 21 2016



THE SATELLITE CLOUD PATTERN AROUND DARBY REMAINS WELL-ORGANIZED, BUT

THE AREA OF COLD TOPS HAS DECREASED A BIT SINCE LAST EVENING.

MICROWAVE PASSES AT 1059 AND 1156 UTC ALSO SHOWED GOOD BANDING

WRAPPING FROM WEST THROUGH SOUTH THROUGH EAST THROUGH NORTH OF THE

CENTER. COMPARISON OF 36 AND 89 GHZ IMAGERY SHOWS THE CENTER SLOPING

UP TO THE SOUTHEAST. THE LATEST SUBJECTIVE DVORAK INTENSITY

ESTIMATES WERE 3.0/45 KT FROM SAB, JTWC AND HFO. THE INITIAL

INTENSITY FOR THIS ADVISORY HAS BEEN KEPT AT 55 KT.



THE CENTER OF DARBY IS NOT EASY TO LOCATE PRECISELY WITH GOES 15

IMAGERY, BUT THE RECENT MICROWAVE PASSES SHOW THAT THE STORM HAS

CONTINUED TO TRACK SOUTH OF WEST. THE TRACK FORECAST HAS AGAIN

SHIFTED VERY SLIGHTLY SOUTHWEST FROM THE PREVIOUS TRACK OVER THE

NEXT 72 HOURS. THE MID-LEVEL RIDGE NORTHWEST OF DARBY WILL STEER THE

STORM WEST SOUTHWEST WITH A VERY GRADUAL TURN TO THE WEST. BEYOND 72

HOURS, DARBY IS EXPECTED TO TURN RATHER SHARPLY TOWARD THE

NORTHWEST AS A LOW ALOFT IN THE GULF OF ALASKA DIGS STRONGLY SOUTH.

THIS IS A RATHER UNUSUAL TRACK FOR A TROPICAL CYCLONE IN THE CENTRAL

PACIFIC, SO THERE IS A GREATER THAN NORMAL AMOUNT OF UNCERTAINTY TO

THE FORECAST. SINCE DARBY CONTINUES TO TRACK TOWARD THE MAIN

HAWAIIAN ISLANDS IT WILL PROBABLY BE NECESSARY TO ISSUE A TROPICAL

STORM WATCH LATER TODAY.



DARBY WILL BE MOVING OVER .5 DEGREE CELSIUS WARMER WATER THE NEXT

COUPLE OF DAYS, WHILE VERTICAL WIND SHEAR IS FORECAST TO INCREASE

SLIGHTLY. DARBY IS EXPECTED TO REMAIN SURROUNDED BY FAIRLY DRY AIR.=