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 364 
 WTPZ45 KNHC 271436
 TCDEP5
 
 Tropical Storm Miriam Discussion Number   6
 NWS National Hurricane Center Miami FL       EP152018
 800 AM PDT Mon Aug 27 2018
 
 The convective structure of Miriam has become better organized
 this morning, with a continued increase in overall banding.  An
 earlier AMSR2 microwave overpass also revealed a well-defined band
 over the southeastern and southern portions of the circulation but
 there was some evidence of northwesterly shear with the center near
 the northwestern edge of the primary convective band.  The initial
 intensity has been increased to 55 kt, which is supported by a
 Dvorak Data T-number of 3.5 from TAFB, earlier AMSU data, and
 recent UW/CIMSS ADT estimates of T3.7 (59 kt).
 
 Satellite fixes indicate that Miriam is moving westward or 270
 degrees at 12 kt.  The cyclone should remain on a westward heading
 over the next 48 hours while it is steered by a large deep-layer
 ridge to the north.  After that time, a large mid- to upper-level
 low to the northeast of the Hawaiian Islands is expected to produce
 a break in the ridge between 140W-150W.  This should cause Miriam to
 turn northwestward, then north-northwestward between days 3 through
 5.  The track guidance is in good agreement on this scenario, but
 there are some differences in Miriam's forward speed after
 recurvature begins.  The ECMWF and UKMET take Miriam much faster
 northward than the remainder of the dynamical models, and the NHC
 track forecast is once again close to the various consensus aids at
 72 h and beyond to account for the speed differences.
 
 The global models suggest that there will be a gradual increase in
 northwesterly shear over Miriam during the next day or so, however,
 this is not expected to prevent the cyclone from becoming a
 hurricane within the next 24 hours.  The moderate shear is forecast
 to relax by Tuesday night, which should allow for additional
 intensification.  The intensity guidance is not quite as aggressive
 as before, and the NHC intensity forecast, which lies between the
 IVCN intensity consensus model and the HFIP corrected consensus, has
 been adjusted slightly downward.  Increasingly southwesterly
 vertical wind shear and cooler waters are expected to cause Miriam
 to weaken late in the forecast period.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  27/1500Z 13.9N 130.5W   55 KT  65 MPH
  12H  28/0000Z 13.9N 132.3W   65 KT  75 MPH
  24H  28/1200Z 13.8N 134.3W   70 KT  80 MPH
  36H  29/0000Z 13.9N 136.3W   75 KT  85 MPH
  48H  29/1200Z 14.1N 138.1W   85 KT 100 MPH
  72H  30/1200Z 15.5N 140.8W   85 KT 100 MPH
  96H  31/1200Z 18.7N 141.8W   75 KT  85 MPH
 120H  01/1200Z 23.3N 143.2W   55 KT  65 MPH
 
 $$
 Forecaster Brown
 
 
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