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 991 
 WTPZ45 KNHC 282035
 TCDEP5
 
 Tropical Storm Miriam Discussion Number  11
 NWS National Hurricane Center Miami FL       EP152018
 200 PM PDT Tue Aug 28 2018
 
 Northwesterly shear has taken a toll on Miriam, with visible
 satellite imagery depicting an exposed low-level center located
 northwest of the deep convection.  Subjective Dvorak T-numbers have
 decreased to 3.0 by both SAB and TAFB, and a blend of the T- and
 CI-numbers yields an initial intensity of 50 kt for this advisory.
 
 Model guidance suggests that the northwesterly shear that is
 currently affecting the cyclone will continue for at least the
 next 24 hours, but it could diminish slightly by late Wednesday,
 allowing for some modest strengthening in 36 to 48 hours.
 Thereafter, a mid- to upper-level trough to the northwest of the
 cyclone is expected to bring about increasing southwesterly shear
 over the system, which is expected to cause steady weakening in 3
 to 4 days.  The cyclone is then expected to become a post-tropical
 cyclone by 120 hours as shear increases even further, and the system
 crosses cooler SSTs.  The official intensity forecast has been
 lowered for much of the forecast period, reflecting both the
 lowering of the initial intensity and the expected continuation of
 the shear.  Although not explicitly shown in the official forecast,
 there is still some chance that Miriam could reach hurricane status
 in a couple of days, before the shear increases.
 
 The initial motion continues to be due west, or 270/11 kt,
 as Miriam continues to be steered around the southern periphery of
 a subtropical ridge. The track forecast philosophy for the next few
 days remains unchanged as the aforementioned mid- to upper-level
 trough northeast of Hawaii weakens the western periphery of the
 ridge, and Miriam is forecast to turn northwestward then
 north-northwestward between the trough and ridge.  There continues
 to be a large spread in the guidance by day 5, with the ECMWF and
 UKMET taking a more vertically coherent system northward, while the
 GFS, HWRF, and HMON turn Miriam westward as the system weakens and
 becomes a more shallow system.  The latter scenario is beginning to
 seem more plausible and the NHC track forecast was adjusted
 southward and westward, but additional changes may be required
 if future forecasts shown a faster rate of demise.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  28/2100Z 14.1N 136.4W   50 KT  60 MPH
  12H  29/0600Z 14.2N 138.0W   50 KT  60 MPH
  24H  29/1800Z 14.4N 139.8W   50 KT  60 MPH
  36H  30/0600Z 14.9N 141.1W   55 KT  65 MPH
  48H  30/1800Z 16.1N 141.7W   60 KT  70 MPH
  72H  31/1800Z 19.3N 142.0W   55 KT  65 MPH
  96H  01/1800Z 22.6N 143.1W   40 KT  45 MPH
 120H  02/1800Z 26.0N 146.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
 $$
 Forecaster Brown/Latto
 
 
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