000 WTPZ44 KNHC 230849 TCDEP4 Tropical Storm Hilary Discussion Number 8 NWS National Hurricane Center Miami FL EP092017 400 AM CDT Sun Jul 23 2017 The cloud pattern of Hilary is gradually becoming better organized, with some convective banding features beginning to develop. The upper-level outflow is well defined over all but the southeastern semicircle of the circulation. Dvorak T-numbers from TAFB and SAB remain at 2.5 so the current intensity is held at 35 kt. This is also consistent with ASCAT data from a few hours ago. The atmospheric and oceanic environment should be quite favorable for intensification during the next few days. The SHIPS guidance indicates that the vertical shear should remain below 10 kt throughout the forecast period, and the global models show a large upper-level anticyclone over Hilary through 4-5 days. Late in the period Hilary is expected to move over cooler SSTs, and this should halt the intensification process. The official intensity forecast shows the system approaching major hurricane status in 72 hours and some of the guidance, including the corrected consensus models, suggest that this could be conservative. Overnight microwave data indicate a bit of a jump to the west-northwest, perhaps as a result of reformation of the center as opposed to large-scale motion. The initial motion estimate is 300/13 kt. A large mid-level anticyclone centered over the southwestern United States or northwestern Mexico should maintain the west-northwestward heading throughout the forecast period. The track model guidance is in agreement on a decrease in forward speed, and the official forecast shows this as well. Later in the period, there is a possibility of some binary interaction with Tropical Storm Irwin currently located some 800 n mi to the west. This, along with a substantial spread in the track models at 4-5 days, adds some uncertainty to the forecast. In any event, the official track forecast is not far from the latest model consensus, and keeps the system well offshore of the coast of Mexico. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 12.5N 101.6W 35 KT 40 MPH 12H 23/1800Z 13.1N 102.8W 45 KT 50 MPH 24H 24/0600Z 13.9N 104.3W 55 KT 65 MPH 36H 24/1800Z 14.7N 105.8W 65 KT 75 MPH 48H 25/0600Z 15.5N 107.3W 80 KT 90 MPH 72H 26/0600Z 17.0N 111.0W 95 KT 110 MPH 96H 27/0600Z 18.0N 115.0W 95 KT 110 MPH 120H 28/0600Z 19.0N 118.5W 85 KT 100 MPH $$ Forecaster Pasch