WTPA42 PHFO 210859

TCDCP2



TROPICAL DEPRESSION FOUR-C DISCUSSION NUMBER   2

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   CP042015

1100 PM HST THU AUG 20 2015



DEEP CONVECTION HAS PERSISTED NEAR THE APPARENT LOW-LEVEL

CIRCULATION CENTER /LLCC/ OF TROPICAL DEPRESSION FOUR-C THIS

EVENING...WITH SOME BANDING FEATURES BEGINNING TO DEVELOP IN RECENT

INFRARED SATELLITE ANIMATIONS. SUBJECTIVE DVORAK INTENSITY ESTIMATES

AT 0600Z CAME IN AT T1.5/25KT FROM PHFO...T2.0/30KT FROM JTWC...AND

T2.5/35KT FROM SAB...WHILE THE CIMSS ADT CURRENT INTENSITY ESTIMATE

HAS RECENTLY RISEN TO 2.5/35KT ALSO. FOUR-C APPEARS TO BE ON THE

VERGE OF TROPICAL STORM STRENGTH...AND MAY BE THERE ALREADY...BUT

HAVE OPTED TO MAINTAIN THE SYSTEM AS A 30 KT DEPRESSION FOR THIS

ADVISORY.



INITIAL MOTION IS ANALYZED AS A SOMEWHAT UNCERTAIN 030/04KT. THE

DEPRESSION IS DRIFTING SLOWLY NORTHWARD ALONG THE WESTERN FLANK OF

A MID-LEVEL RIDGE WHICH EXTENDS WESTWARD FROM THE HAWAIIAN ISLANDS

TO AROUND 170W. THE GUIDANCE SUITE REMAINS IN REASONABLY GOOD

AGREEMENT THROUGH 48 HOURS...INDICATING A SLOW NORTH TO NORTHWEST

MOTION AS THE TROPICAL CYCLONE MOVES ALONG THE WESTERN PERIPHERY OF

THE RIDGE. MOST OF THE GUIDANCE THEN TURNS THE CYCLONE TO THE NORTH

AND EVENTUALLY NORTH-NORTHEAST BEYOND 72 HOURS...WITH AN INCREASE

IN FORWARD SPEED...AS THE CYCLONE APPARENTLY BECOMES CAUGHT UP IN A

DEEPENING MID-LATITUDE TROUGH ALONG THE INTERNATIONAL DATELINE. THE

NEW FORECAST TRACK IS VERY SIMILAR TO THE PREVIOUS TRACK...ALTHOUGH

A BIT SLOWER...AND IS ALSO VERY SIMILAR TO THE TVCE TRACK CONSENSUS

THROUGH 48 HOURS...THEN IS SLIGHTLY TO THE RIGHT AND FASTER THAN THE

PREVIOUS TRACK BEYOND TAU 72. THE NEW FORECAST TRACK FOR 96 HOURS

AND BEYOND IS NOT AS FAST NOR AS FAR TO NORTH AND EAST AS THE

CONSENSUS HOWEVER.



FOUR-C IS MOVING OVER VERY WARM WATERS AND IS WITHIN A LOW SHEAR

ENVIRONMENT AT PRESENT. MOST OF THE INTENSITY GUIDANCE STRENGTHENS

THE CYCLONE TO A TROPICAL STORM WITHIN THE NEXT 12 HOURS...AND SO

DOES THE OFFICIAL FORECAST. IT SHOULD BE NOTED THAT THE SHIPS RAPID

INTENSIFICATION INDEX SHOWS A 41 PERCENT CHANCE OF A 25 KT INTENSITY

INCREASE DURING THE NEXT 24 HOURS. GIVEN THE FAVORABLE INITIAL

CONDITIONS AND APPARENT IMPROVING ORGANIZATION...IT WOULD NOT BE

SURPRISING IF THE CYCLONE STRENGTHENS MORE QUICKLY THAN CURRENTLY

FORECAST IN THE NEAR TERM. SLOW STRENGTHENING IS FORECAST FOR

TAU 24 THROUGH TAU 72...IN GOOD AGREEMENT WITH THE IVCN CONSENSUS.

THE INTENSITY FORECAST LEVELS OFF AT 50 KT BEYOND 72 HOURS...WHEN

INCREASING WEST/NORTHWEST SHEAR MAY BEGIN TO IMPACT THE CYCLONE

AS IT MOVES INTO HIGHER LATITUDES AND DRAWS CLOSER TO THE

MID-LATITUDE TROUGH.





FORECAST POSITIONS AND MAX WINDS



INIT  21/0900Z 15.6N 177.0W   30 KT  35 MPH

 12H  21/1800Z 15.9N 177.0W   35 KT  40 MPH

 24H  22/0600Z 16.6N 177.5W   40 KT  45 MPH

 36H  22/1800Z 17.4N 178.3W   45 KT  50 MPH

 48H  23/0600Z 18.3N 179.3W   45 KT  50 MPH

 72H  24/0600Z 20.1N 179.7E   50 KT  60 MPH

 96H  25/0600Z 22.0N 180.0E   50 KT  60 MPH

120H  26/0600Z 25.0N 179.0W   50 KT  60 MPH



$$

FORECASTER JACOBSON/BIRCHARD