WTPZ44 KNHC 242034

Hurricane Hilary Discussion Number 14
NWS National Hurricane Center Miami FL EP092017
400 PM CDT Mon Jul 24 2017

Hilary continues to display a small central core with very deep convective tops and lots of banding in the outer circulation. Although an eye is not apparent in visible imagery, WindSAT microwave data from earlier show that the hurricane has a distinct eye underneath the cloud canopy. Satellite estimates continue to increase, so the initial wind speed is set to 75 kt, close to the latest SAB fix.

The hurricane has been strengthening quickly during the past 24 h, near the threshold of rapid intensification. With no significant changes to the favorable oceanic and atmospheric environments forecast, there is good reason to show a similar rate of strengthening for the first 24 hours of the forecast. After that time, models are indicating an increase in northerly wind shear, partially associated with an enhanced anticyclonic outflow from TS Irwin. This might limit the peak intensity, so the wind speed forecast has been leveled off on day 2. The latest model guidance has come in closer to the previous official forecast, so little change has been made in the new NHC intensity prediction. Some weakening is likely at longer range due to cooler SSTS, entrainment of drier air, and binary interaction with Irwin.

The initial motion estimate is 300/7 kt. A ridge that extends into the eastern Pacific from the southwestern United States is forecast to strengthen slightly over the next couple of days, which should steer Hilary a little to the left and a bit faster during that time. The long-range forecast is quite challenging with the threat of binary interaction with Irwin, leading to widely divergent solutions by days 4-5. While the GFS keeps Hilary far separated from Irwin on the northeastern side of the guidance envelope, its ensemble mean is much more in the pack of the guidance, suggesting the latest GFS solution is not very likely. The UKMET and ECMWF continue to show rare TC binary interaction and merger scenarios which, although scientifically pleasing to see, lead to large errors potentially. Overall, the model trend toward more interaction with Irwin continues, which led to a westward shift of the latest NHC prediction at days 3-5.


INIT 24/2100Z 14.5N 104.9W 75 KT 85 MPH 12H 25/0600Z 14.9N 106.0W 85 KT 100 MPH 24H 25/1800Z 15.5N 107.8W 100 KT 115 MPH 36H 26/0600Z 16.1N 110.0W 105 KT 120 MPH 48H 26/1800Z 16.6N 112.0W 105 KT 120 MPH 72H 27/1800Z 17.7N 115.8W 95 KT 110 MPH 96H 28/1800Z 18.7N 119.3W 80 KT 90 MPH 120H 29/1800Z 19.5N 122.5W 70 KT 80 MPH

$$ Forecaster Blake