826 WTPZ41 KNHC 030252 TCDEP1 Hurricane Orlene Discussion Number 18 NWS National Hurricane Center Miami FL EP162022 900 PM MDT Sun Oct 02 2022 Orlene appears to be slowly weakening this evening. 1-minute GOES-17 IR satellite imagery shows persistent bursting cloud tops below -80 C in the northern semicircle of the hurricane, likely still associated with its eyewall. A 0116 UTC F-17 SSMIS microwave pass also showed an eyewall fragment remains in connection to these very cold cloud tops, though comparing microwave with geostationary satellite suggests the hurricane is starting to become more tilted. There are also subtle hints that upper-level westerly flow is beginning to undercut the cirrus on the western side of the convective plume. The subjective Dvorak intensity estimates were CI 5.5/102-kt from TAFB and CI 5.0/90-kt from SAB. However, the Final T-numbers have been slowly decreasing and the initial intensity was set to 90 kt for this advisory. The intensity forecast is somewhat tricky for Orlene over the next day or so. Deep-layer (200-850 mb) southwesterly vertical wind shear is steadily increasing over Orlene and is now over 20-kt in both the latest GFS- and ECMWF-based SHIPS guidance. This shear is expected to increase to 30-kt in the next 12-24 h, and will likely play a role in helping to import drier mid-level air into the core of the small hurricane. However, during this period, Orlene will also be traversing over very warm sea-surface temperatures, above 30 degrees Celsius, which could help the deep convection to remain quite vigorous, especially during the diurnal max period. Thus, while weakening appears likely, the rate of weakening has a higher than normal uncertainty. The intensity guidance this cycle has a faster rate of weakening, and the latest NHC intensity forecast was shifted in that direction, though not quite as dramatic. Orlene is still forecast to be a hurricane as it makes landfall in mainland Mexico sometime on Monday. After landfall, the small system should quickly weaken over the higher terrain of Mexico, with dissipation likely by 48 hours. The hurricane appears to be moving a little more east of due north tonight, with the estimated motion at 010/7 kt. Orlene should continue this general heading for the next 12 to 24 hours, remaining steered by a mid-level ridge to its east, until the hurricane makes landfall at some point on Monday along the southwestern coast of Mexico. The track guidance this cycle has made a shift to the west, likely due to some of the guidance (GFS, HWRF) showing the tropical cyclone de-coupling from the deep convection in the immediate short-term. Since that process has not yet occurred, the track forecast this cycle was only shifted slightly west of the prior track, though is notably slower with the speed of Orlene shortly after the system makes landfall. Key Messages: 1. Hurricane conditions are likely ongoing near Islas Marias tonight. A Hurricane Warning is in effect for a portion of west-central mainland Mexico, where hurricane conditions are expected on Monday with tropical storm conditions beginning overnight. Preparations to protect life and property should be rushed to completion. 2. A dangerous storm surge is likely to cause coastal flooding in the Islas Marias and along the coast of mainland Mexico in the warning area in regions of onshore winds. 3. Heavy rainfall from Orlene is expected to lead to flash flooding, as well as possible landslides in areas of rugged terrain of southwest Mexico through Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 21.4N 106.5W 90 KT 105 MPH 12H 03/1200Z 22.1N 106.4W 80 KT 90 MPH 24H 04/0000Z 22.9N 106.2W 70 KT 80 MPH...ON THE COAST OF MEXICO 36H 04/1200Z 23.6N 105.9W 35 KT 40 MPH...INLAND 48H 05/0000Z...DISSIPATED $$ Forecaster Papin/Blake