ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM HURRICANE DARBY DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 PM PDT FRI JUL 15 2016 Darby's eye became a little less well-defined and central convection weakened somewhat a few hours ago, and Dvorak data T-number from both TAFB and SAB were lowered to 4.5. Recently, however, cloud tops have been cooling around the eye and based on the Dvorak Current Intensity rules the maximum winds are kept at 90 kt for this advisory. The hurricane has well-defined upper-level outflow over all but the southeastern portion of the circulation. The tropical cyclone is in a weak-shear environment and is likely to remain so for the next several days. Whereas this would seem to favor the system to maintain strength or even intensify further, the future thermodynamic environment is not favorable. Darby is approaching a cold tongue in the ocean and should pass over SSTs near 24 deg C within a couple of days. Satellite imagery also shows an extensive stratocumulus field ahead of the hurricane, which is indicative of stabler air. These factors should cause Darby to be on a weakening trend very soon. The official intensity forecast is in close agreement with the model consensus, IVCN, and with the previous NHC forecast. Darby has moved a little more to the right of the previous track over the past several hours, but using a 12-hour average yields a motion estimate of 295/8. The mid-level flow on the south side of a subtropical ridge should cause the tropical cyclone to turn westward over the next several days. A slight northward adjustment was made to the official forecast, mainly due to the more northward short-term motion of Darby. The new official forecast lies on the southern side of the guidance envelope and is close to the latest GFS and ECMWF solutions, which are themselves in close agreement. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 17.3N 122.1W 90 KT 105 MPH 12H 16/1200Z 17.7N 123.4W 85 KT 100 MPH 24H 17/0000Z 18.1N 125.1W 80 KT 90 MPH 36H 17/1200Z 18.4N 126.7W 75 KT 85 MPH 48H 18/0000Z 18.7N 128.8W 70 KT 80 MPH 72H 19/0000Z 19.3N 133.3W 55 KT 65 MPH 96H 20/0000Z 20.0N 138.0W 45 KT 50 MPH 120H 21/0000Z 20.0N 142.5W 40 KT 45 MPH $$ Forecaster Pasch NNNN