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ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Hurricane John Discussion Number 9 NWS National Hurricane Center Miami FL EP122018 300 PM MDT Tue Aug 07 2018 The eye of John has become more distinct in visible and infrared satellite imagery during the past few hours, however the surrounding convective clouds tops have warmed, and a 1642 UTC AMSU microwave overpass indicated that the eyewall was open over the northwestern portion of the circulation. Although objective Dvorak T-numbers have increased to T5.6, subjective estimates from TAFB and SAB are unchanged so the initial intensity is kept at 90 kt. There is still an opportunity for John to become a major hurricane tonight or early Wednesday while it remains over warm water and in a low shear environment. After that time, the hurricane will be moving over decreasing SSTs and into a less favorable thermodynamic environment. These conditions should result in steady to rapid weakening and John is forecast to become a post-tropical cyclone by day 4 when it is over SSTs of 20-21C. There is significant spread in the intensity guidance as to how rapid John will spin down. The NHC forecast is a little higher than the ICON consensus model, but shows a faster rate of weakening than the statistical guidance. John is moving northwestward or 320/9 kt. The hurricane should continue moving northwestward around the western side of a mid-level ridge over northern Mexico during the next 2-3 days. After that time, the system should turn westward as it weakens and comes under the influence of the low-level flow. The track guidance remains in excellent agreement and the new NHC track is essentially an update of the previous advisory. Although the core of John is forecast to remain well offshore of the Baja California Peninsula, an eastward shift of the forecast track or an unexpected increase in the size of the outer wind field of the hurricane could bring tropical-storm-force winds close to the west coast of the peninsula. In addition, a surge of moisture around John's outer circulation is expected to bring some locally heavy rainfall to portions of Baja California Sur during the next couple of days. Therefore, interests in the southern portion of the Baja California Peninsula should monitor the progress of John. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 18.7N 110.5W 90 KT 105 MPH 12H 08/0600Z 19.9N 111.6W 100 KT 115 MPH 24H 08/1800Z 21.5N 113.3W 95 KT 110 MPH 36H 09/0600Z 23.0N 115.2W 80 KT 90 MPH 48H 09/1800Z 24.4N 117.3W 65 KT 75 MPH 72H 10/1800Z 26.6N 121.3W 45 KT 50 MPH 96H 11/1800Z 27.0N 124.7W 35 KT 40 MPH...POST-TROPICAL 120H 12/1800Z 27.0N 127.3W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown NNNN