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WTPZ45 KNHC 201435
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 forward speed differences late in the period. The ECMWF and UKMET are faster by days 4 and 5, while the GFS and GEFS ensemble mean are slower. Also, the latest HWRF is well south and west of the rest of the guidance envelope. The new NHC track forecast is near the previous one through 48 hours and has been shifted a little to the left after that time, and lies between the GFS and ECMWF solutions and their respective ensemble means.

The next advisory on Darby will be issued by the Central Pacific Hurricane Center in Honolulu, Hawaii.

FORECAST POSITIONS AND MAX WINDS

INIT 20/1500Z 19.9N 139.8W 50 KT 60 MPH 12H 21/0000Z 19.7N 141.6W 50 KT 60 MPH 24H 21/1200Z 19.4N 144.0W 50 KT 60 MPH 36H 22/0000Z 19.0N 146.4W 50 KT 60 MPH 48H 22/1200Z 18.8N 148.6W 50 KT 60 MPH 72H 23/1200Z 19.0N 152.0W 45 KT 50 MPH 96H 24/1200Z 20.5N 153.5W 45 KT 50 MPH 120H 25/1200Z 24.0N 155.0W 40 KT 45 MPH

$$ Forecaster Brennan



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