ZCZC HFOTCDCP3 ALL TTAA00 PHFO DDHHMM Hurricane Miriam Discussion Number 21 NWS Central Pacific Hurricane Center Honolulu HI EP152018 1100 PM HST Thu Aug 30 2018 The satellite presentation of Miriam has changed little over the past 6 hours, but a slight improvement in the convective cloud coverage over the low level circulation center appears to have occurred during the past several hours. A large area of -65 to -80C cloud tops remain over the difficult to locate low level circulation center. Several microwave passes since 30/2330Z have been helpful in confidently determining the center location of Miriam as well as estimating the motion of the system this evening, with a 0346Z Windsat and 0636Z MHS Metop-A pass particularly useful. Subjective Dvorak fixes from PHFO, SAB, and JTWC all came in with intensity estimates of 4.5 (77 knots) with the Advanced Dvorak Technique from UW-CIMSS slightly lower at 4.3 (72 knots). Several images around 31/06Z showed the center sufficiently within the deeper colder cloud tops to yield a T5.0 (90 knots). Based on the slight improvement in the convective cloud coverage over Miriam, and several images around the synoptic hour yielding higher intensity estimates, the initial intensity for this advisory has been weighted slightly higher than the intensity estimates indicated from the various agencies. The initial intensity has been raised to 80 knots with this advisory with a motion of 360/07 knots. Miriam is being steered by a large subtropical ridge to the northeast and a mid-upper level trough to the north and northwest. A general northward motion is expected to continue tonight through Friday night as the system remains deep and intact following the deep layer steering flow. Strong southwesterly shear is then expected to decouple the system by late Friday night 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 shifted slightly to the right through 48 hours to better align with the HWRF, TVCE, HCCA and GFS which indicate a fairly deep circulation. Beyond 48 hours the official forecast track lies roughly on top of the previous forecast as the system becomes increasingly shallow and steered by the low level trade wind flow. It appears that the window for Miriam to intensify has closed, with the latest UW-CIMSS vertical shear analysis showing 21 knots of southwesterly shear over the core of the system. The hurricane is expected to slowly weaken tonight and Friday as shear steadily increases. Rapid weakening is then forecast Friday night and Saturday as Miriam moves into a region of strong southwesterly shear of 35 to 50 knots and moves over unfavorable sea surface temperatures below 26C. Miriam is forecast to become a remnant low by late Sunday. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 17.4N 141.5W 80 KT 90 MPH 12H 31/1800Z 18.7N 141.3W 75 KT 85 MPH 24H 01/0600Z 20.5N 141.5W 65 KT 75 MPH 36H 01/1800Z 22.3N 142.3W 50 KT 60 MPH 48H 02/0600Z 24.2N 143.6W 35 KT 40 MPH 72H 03/0600Z 27.7N 147.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 04/0600Z 31.0N 152.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 05/0600Z...DISSIPATED $$ Forecaster Jelsema NNNN