000 WTPZ44 KNHC 252042 TCDEP4 Hurricane Hilary Discussion Number 18 NWS National Hurricane Center Miami FL EP092017 300 PM MDT Tue Jul 25 2017 Hilary continues to have a somewhat asymmetric presentation on the latest satellite imagery, with an eye feature in the northwestern portion of the central dense overcast, suggestive of some northwesterly shear. The initial wind speed remains 90 kt since there have been no significant changes to the satellite estimates. Higher wind shear is not far away from the hurricane, as evidenced by southward-moving cirrus clouds moving toward the center in the northern semicircle. Thus the window of time for Hilary to intensify may be closing, and little change in wind speed is shown for the next day or so. Afterward, gradually cooling SSTs, entrainment of drier air, and interaction with Hurricane Irwin is likely to cause more significant weakening. The NHC forecast is reduced from the previous one in the near term due to the shear, and at long range as Hilary probably moves over cold waters. This is not a particularly confident forecast at days 4-5 due to the interaction with Irwin. The initial motion estimate is the same as previous, 285/10 kt. A mid-tropospheric ridge extending westward from the southwestern United States should cause Hilary to continue on a west to west-northwestward track for the next several days. In a few days, however, Hilary is likely to pass close to Hurricane Irwin. While Irwin won't affect Hilary too much, the bulk of the guidance is showing Hilary slowing down and turning slightly left as Irwin pulls on Hilary's circulation. Model guidance has become more divergent after day 3, with the GFS indicating a northwestward motion due to the ridge weakening along 120-125W. The other guidance has been more consistent, so only small changes were made to the latest NHC forecast, which remains generally south and west of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 15.5N 108.8W 90 KT 105 MPH 12H 26/0600Z 15.9N 110.5W 95 KT 110 MPH 24H 26/1800Z 16.4N 112.7W 95 KT 110 MPH 36H 27/0600Z 16.9N 114.8W 90 KT 105 MPH 48H 27/1800Z 17.5N 116.8W 85 KT 100 MPH 72H 28/1800Z 18.7N 120.4W 80 KT 90 MPH 96H 29/1800Z 19.7N 124.0W 70 KT 80 MPH 120H 30/1800Z 20.5N 127.5W 50 KT 60 MPH $$ Forecaster Blake