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 WTPA43 PHFO 311502
 Hurricane Miriam Discussion Number  22
 NWS Central Pacific Hurricane Center Honolulu HI   EP152018
 500 AM HST Fri Aug 31 2018
 Miriam is beginning to feel the effects of increasing southwesterly 
 shear, with the latest UW-CIMSS analysis depicting 30 knots of
 shear over the system. Despite the increasing shear, the system
 continues to hold a large area of deep convection with -65 to -80C
 cloud tops over the low level circulation center. The latest
 subjective Dvorak intensity estimates from PHFO, SAB, and JTWC all
 came in at 4.5 (77 knots) with the Advanced Dvorak Technique from
 UW-CIMSS slightly higher 4.6 (80 knots). The initial intensity for
 this advisory will be held at 80 knots based on a blend of these
 intensity estimates and recent satellite imagery suggesting the
 intensity could be as high as T5.0 (90 knots). The motion is
 somewhat uncertain given the deep convection over the center of
 Miriam and a lack of timely microwave data. Using a combination of
 interpolation of the movement when confidence in the center position
 was high, along with current satellite trends, the motion is set at
 005/09 knots.  
 Hurricane Miriam is being steered by a large subtropical ridge to 
 the east and northeast along with a deep mid-upper level trough to 
 the north and northwest. A general northward motion is expected to 
 continue today and tonight as the system remains fairly deep and 
 follows the deep layer steering flow. Strong southwesterly shear is 
 then expected to decouple the system by late tonight or early 
 Saturday, and this is expected to result in a turn toward the 
 northwest with Miriam being steered by the low level trade wind 
 flow. The official forecast has been nudged slightly to the left 
 through 24 hours based on the estimated initial motion slightly to 
 the east of due north. Beyond 24 hours the track forecast lies 
 virtually on top of the forecast from the previous advisory. The 
 track forecast closely follows the latest TVCE/HCCA consensus 
 guidance through 48 hours, then is slightly to the left of the 
 consensus guidance beyond 48 hours expecting a fairly shallow
 system being steered by the trades and more in line with the GFS
 Miriam peaked at an intensity of 80 knots overnight, a high end 
 category one hurricane, and it appears likely that this will be as 
 strong as the system gets. Southwesterly shear is forecast to 
 increase further today, with 35 to 50 knots of shear expected over 
 the cyclone tonight through the end of the forecast period, while 
 the system is passing over sea surface temperatures below 26C.
 Rapid weakening should begin later today, with Miriam expected to
 drop below hurricane strength late today or tonight, and become a
 post-tropical remnant low Sunday or Sunday night. The intensity
 forecast is closely aligned with the latest dynamical and consensus
 guidance which were all in good agreement.
 INIT  31/1500Z 18.3N 141.2W   80 KT  90 MPH
  12H  01/0000Z 19.6N 141.2W   70 KT  80 MPH
  24H  01/1200Z 21.4N 141.7W   55 KT  65 MPH
  36H  02/0000Z 23.2N 142.8W   45 KT  50 MPH
  48H  02/1200Z 25.1N 144.4W   35 KT  40 MPH
  72H  03/1200Z 28.5N 148.4W   30 KT  35 MPH...POST-TROP/REMNT LOW
  96H  04/1200Z...DISSIPATED
 Forecaster Jelsema
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