WTPA43 PHFO 222107

TCDCP3



TROPICAL STORM DARBY DISCUSSION NUMBER  45

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP052016

1100 AM HST FRI JUL 22 2016



Deep convection associated with Darby was mainly in the

system's northern semicircle with persistent tops colder than

-70C. An SSMIS pass from 1732 UTC indicated the system was tilted

toward the east. The first Air Force Reserve 53rd Weather

Reconnaissance Squadron mission into Darby found maximum SFMR winds

of just over 50 knots but the initial passes had difficulty

determining the location of the low level center. Based on the

recon data thus far, the tropical storm force radius was expanded

slightly in the northern semicircle and Darby has been held at 50

kt for this advisory package.



Darby is estimated to be moving at 270/10 kt to the south of a

ridge. This ridge is forecast to weaken due to a low pressure system

digging southward to the north of Darby. This is expected to

decrease the forward motion over the next day, and increase the

amount of vertical shear on the tropical cyclone this weekend. The

trusted objective aids are consistent with this scenario but have

shifted southward slightly with some solutions indicating landfall

over the Big Island. As a result, the current forecast has been

shifted southward a bit and is between the dynamical consensus and

the previous forecast. Given current guidance trends, a direct

impact on the Big Island and Maui is a distinct possibility this

weekend.



The main factors affecting the intensity forecast include marginal

sea surface temperatures, the amount and timing of vertical wind

shear, and the effects of any potential interactions with the

Hawaiian Islands. Sea surface temperatures will remain marginal near

26.5C over the next couple of days but vertical shear is expected to

increase as the previously mentioned upper level trough digs farther

south. This shear increase is not expected to be significant until

later this weekend. Thus, the forecast is close to the previous

package which has Darby only slowly weakening and maintains the

cyclone as a tropical storm through the weekend. This is close to

the intensity consensus guidance. Note that interactions with the

main Hawaiian Islands may cause significant disruptions to Darby and

so the intensity forecast confidence is not high at this time.



Interests outside of the warning areas in the Hawaiian islands

should monitor the progress of Darby, as it could eventually have

impacts on all islands through early next week. Remember, it is

important not to focus too closely on the exact track and intensity

forecasts because the average track error 72 hours out is near 100

miles, while the average intensity error is about 15 kt. In

addition, the hazards of a tropical cyclone can extend over a broad

area well away from the center.





FORECAST POSITIONS AND MAX WINDS



INIT  22/2100Z 18.5N 151.0W   50 KT  60 MPH

 12H  23/0600Z 18.8N 152.5W   50 KT  60 MPH

 24H  23/1800Z 19.4N 154.4W   45 KT  50 MPH

 36H  24/0600Z 20.4N 155.7W   45 KT  50 MPH

 48H  24/1800Z 21.4N 156.9W   40 KT  45 MPH

 72H  25/1800Z 23.8N 159.3W   40 KT  45 MPH

 96H  26/1800Z 26.0N 161.5W   35 KT  40 MPH

120H  27/1800Z 30.0N 162.5W   30 KT  35 MPH



$$

Forecaster Kodama