ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM RRA Hurricane Hilary Discussion Number 7...Retransmitted NWS National Hurricane Center Miami FL EP092023 900 PM MDT Thu Aug 17 2023 Hilary continues to rapidly intensify. The presentation on infrared satellite imagery has become very impressive, and the hurricane now has a thick ring of -70 to -75 C eyewall cloud tops surrounding the eye which continues to warm. Earlier AMSR2 and GMI microwave imagery showed a similarly impressive structure, with a solid eyewall on both 89-GHz and 37-GHz channels. While the most recent subjective Dvorak intensity estimates are constrained from increasing as much as the satellite presentation would suggest, the objective estimates from UW-CIMSS have been rapidly increasing, with the latest estimate from ADT at T6.3/122 kt, AiDT at 112 kt, and 107 kt from D-PRINT. Hilary's initial intensity will be set at 110 kt for this advisory, favoring the objective estimates. The hurricane has maintained a west-northwestward motion tonight, estimated at 300/12 kt. The mid-level ridge currently steering Hilary is soon forecast to shift eastward as a mid- to upper-level cutoff low swings in from the west and parks itself near the central California coast. This pattern should result in Hilary starting to turn northwestward and the north-northwestward over the next 24-36 hours. A turn more northward should begin by this weekend with some gradual acceleration as the hurricane is captured downstream of the cutoff low. The track guidance this cycle remains tightly clustered, and only slight adjustments to the forecast track were made this cycle. This track forecast remains in good agreement with the corrected consensus aid (HCCA). Since the forecast track continues to be roughly parallel to the coastline north of the central Baja peninsula to the California border, it very difficult to know if the center will remain just offshore or move over the peninsula before reaching the southwestern United States. The rapid intensification episode of Hilary is expected to continue for at least another 12 hours, and the latest forecast intensity now takes the hurricane to 130 kt in that time frame. Afterwards, there is an interesting difference between the statistical-dynamical models (SHIPS and LGEM) which show a peak intensity in about 24 hours, and the hurricane-regional models which show a peak a bit earlier before gradual weakening begins. While there are few signs of an imminent eyewall replacement cycle based on the last few microwave passes, it is possible one could occur in another day or so. The large 34-kt wind field of the hurricane could also start to upwell some cooler waters out ahead of the inner core in 24-36 hours. Thus, some gradual weakening is now forecast to begin during this time period with a faster rate of weakening as the hurricane crosses a sharp temperature gradient to the west of the Baja Californian peninsula. The official forecast is above the intensity guidance in the short-term, but falls back to the consensus aids beyond 36 h. The surface circulation is likely to dissipate as it pushes far inland in 96 hours, but a point as a remnant low will still be shown to maintain a forecast track over the southwestern United States. KEY MESSAGES: 1. Heavy rainfall associated with Hilary may produce areas of flash flooding and result in landslides over portions of the Baja California Peninsula from late Friday into late Sunday. Rainfall impacts from Hilary within the Southwestern United States are expected to peak this weekend into Monday. Flash, urban, and arroyo flooding is possible with the potential for significant impacts. 2. The threat of hurricane-force wind impacts is increasing along the west-central coast of the Baja California Peninsula, and the government of Mexico has issued a hurricane watch for a portion of the west coast of the Baja California peninsula. Tropical storm conditions are expected to spread across the southern portion of the Baja California Peninsula by late Friday where a Tropical Storm Warning is in effect. 3. The threat of significant wind impacts continues to increase for the northern portions of the Baja California Peninsula and the Southwestern United States, especially in areas of mountainous terrain. Although it is too soon to determine the location and magnitude of these impacts, interests in these areas should monitor the progress of Hilary and updates to the forecast. Watches could be issued for portions of this area on Friday. 4. Large swells from Hilary will spread northward along the coast of southwestern Mexico and the Baja California Peninsula. These swells will reach the Gulf of California and northern portions of the Baja California Peninsula later this weekend. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 16.7N 110.0W 110 KT 125 MPH 12H 18/1200Z 17.7N 111.4W 130 KT 150 MPH 24H 19/0000Z 19.4N 112.6W 125 KT 145 MPH 36H 19/1200Z 21.5N 113.6W 115 KT 130 MPH 48H 20/0000Z 24.0N 114.3W 100 KT 115 MPH 60H 20/1200Z 27.2N 115.0W 70 KT 80 MPH 72H 21/0000Z 30.7N 116.1W 55 KT 65 MPH 96H 22/0000Z 39.0N 118.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 23/0000Z...DISSIPATED $$ Forecaster Papin NNNN