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 WTPZ45 KNHC 270835
 Tropical Storm Miriam Discussion Number   5
 NWS National Hurricane Center Miami FL       EP152018
 200 AM PDT Mon Aug 27 2018
 Miriam's cloud pattern and overall convective organization have
 continued to improve, with a tight comma-cloud pattern now evident
 in infrared imagery.  Two recent ASCAT passes around 0600Z indicate
 that the low-level center is now located just inside the northwest
 quadrant of the convective comma head, and that the radius of
 maximum winds (RMW) is still about 20 nmi that was ascertained from
 earlier passive microwave low-level ring data. The ASCAT data
 indicated peak winds of only 37 kt, but this is likely an
 underestimate of Miriam's actual intensity due to a) the data having
 been located near the swath edge and b) due to Miriam's small RMW.
 The advisory intensity of 50 kt is based on a average of subjective
 and objective satellite intensity estimates that range from T3.0/45
 kt to T3.6/57 kt, respectively. The previous advisory's 34-kt wind
 radii remain unchanged based on the aforementioned ASCAT wind data.
 Miriam is now moving due west or 270/13 kt. There are no significant
 changes to the previous forecast track or reasoning. The cyclone is
 expected to maintain a general westward motion for the next 72 h as
 Miriam moves along the southern periphery of a strong ridge to its
 north. By 96 h and beyond, Miriam is forecast to move northward to
 north-northwestward through a break in the subtropical ridge near
 created by a strong mid- to upper-level trough/low forecast to drop
 southward between 140W-150W from the upper-low's current position
 over the central North Pacific. The latest model guidance has come
 into better agreement on both the timing and location of the
 northward turn, although noticeable speed differences still exist,
 with the ECMWF and UKMET being the faster models. The NHC official
 forecast track lies close to the previous advisory track, and is
 just a tad north of the HCCA, FSSE, and TVCN consensus models.
 Steady strengthening still appears likely for the next couple of
 days. Miriam's upper-level outflow has improved some and is less
 restricted in the northwest quadrant, a signal that the shear is
 beginning to relax, which would support steady or significant
 strengthening in the short term. By 36-48 h, however, the shear is
 forecast by the global models to again increase to 15-20 kt from the
 northwest, which should inhibit the intensification process during
 that time. Around 72 h, the shear is expected to decrease yet again,
 followed by another increase in the shear. Rather than showing
 roller-coaster fluctuations, the NHC intensity forecast just calls
 for steady strengthening through 48-72 h, followed by a gradual
 weakening trend, which mirrors the previous advisory trend and is
 close to an average of the HCCA and FSSE intensity models.
 INIT  27/0900Z 13.9N 129.2W   50 KT  60 MPH
  12H  27/1800Z 13.9N 130.9W   60 KT  70 MPH
  24H  28/0600Z 13.8N 133.0W   70 KT  80 MPH
  36H  28/1800Z 13.8N 135.1W   80 KT  90 MPH
  48H  29/0600Z 14.0N 137.1W   90 KT 105 MPH
  72H  30/0600Z 14.7N 140.2W   90 KT 105 MPH
  96H  31/0600Z 17.5N 141.6W   80 KT  90 MPH
 120H  01/0600Z 22.0N 142.4W   55 KT  65 MPH
 Forecaster Stewart
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