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 039 
 WTPZ45 KNHC 280838
 TCDEP5
 
 Tropical Storm Miriam Discussion Number   9
 NWS National Hurricane Center Miami FL       EP152018
 200 AM PDT Tue Aug 28 2018
 
 Miriam's cloud pattern has still not improved very much, with
 microwave data showing the low-level center still slightly
 displaced from the deep convection due to about 10 kt of
 northwesterly shear.  Dvorak estimates from TAFB and SAB, as well
 as the UW-CIMSS SATCON, all remain near 55 kt, which will remain
 Miriam's initial intensity.  Miriam is expected to remain over warm
 waters and in a relatively low-shear environment for the next 48-72
 hours, which should allow the cyclone to strengthen modestly over
 the next few days.  At 72 hours and beyond, Miriam will encounter
 significantly stronger shear ahead of an amplifying mid- to
 upper-level trough northeast of the Hawaiian Islands, and the
 cyclone will also move over sub-26C waters.  These conditions should
 cause a rather quick weakening trend on days 4 and 5, with Miriam
 barely hanging on as a tropical storm by the end of the forecast
 period.  The intensity guidance has decreased somewhat on this
 forecast cycle, probably because Miriam has less time before it
 reaches stronger shear.  The updated NHC intensity forecast lies
 between the HCCA guidance and the IVCN intensity consensus, with the
 forecast peak intensity just slightly below that of the previous
 advisory.
 
 The initial motion is due westward, or 270/10 kt, with Miriam
 located along the southern periphery of the subtropical ridge.  The
 amplifying trough northeast of Hawaii is breaking down the ridge and
 should cause Miriam to turn sharply toward the northwest and north
 between days 2 and 4.  There are significant speed differences among
 the models by days 4 and 5, related to how deep Miriam is when it
 interacts with the deep-layer trough.  The ECMWF, which maintains a
 deeper, stronger vortex, shoots Miriam quickly northward, ending up
 more than 600-700 nm north of where the GFS and HWRF models have the
 cyclone by day 5.  Given where the consensus aids lie between those
 two extremes, the updated NHC track forecast has been slowed down a
 bit from the previous forecast.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  28/0900Z 14.0N 133.5W   55 KT  65 MPH
  12H  28/1800Z 14.0N 135.1W   60 KT  70 MPH
  24H  29/0600Z 14.1N 137.1W   70 KT  80 MPH
  36H  29/1800Z 14.4N 138.8W   75 KT  85 MPH
  48H  30/0600Z 15.1N 140.1W   80 KT  90 MPH
  72H  31/0600Z 17.9N 141.0W   80 KT  90 MPH
  96H  01/0600Z 21.5N 141.5W   55 KT  65 MPH
 120H  02/0600Z 26.0N 144.0W   35 KT  40 MPH
 
 $$
 Forecaster Berg
 
 
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